Publikationen

Zusammenfassung

Muscle architecture, particularly the pennation angle, plays a crucial role in force transmission and muscle function. The tibialis anterior muscle exhibits compartment-specific architectural patterns that may contribute differentially to force production. Three-dimensional ultrasound (3DUS) enables comprehensive spatial assessment of muscle architecture, overcoming limitations of traditional 2D ultrasound imaging. Twelve participants performed graded isometric dorsiflexion contractions at passive, 10%, 20%, 40%, and 80% of maximum voluntary contraction (MVC) at −10° ankle dorsiflexion. 3DUS data were acquired using an automated linear scanning system. Muscle architecture was analyzed using two complementary pipelines: MATLAB-based processing for pennation angles and central aponeurosis metrics with compartment-specific assessment, and Python-based streamline fiber tracking for fiber lengths and curvatures. Pennation angles increased progressively with contraction intensity (passive: 10.6° 0.4°; 80% MVC: 12.6° 0.4°, ), with the deep compartment showing significantly higher angles than the superficial one ( ). Fiber length decreased significantly with contraction intensity (passive: 67.8 mm 2.8 mm; 80% MVC: 58.7 mm 1.8 mm, ), while fiber curvature decreased significantly (passive: 0.48 1/100 mm 0.02 1/100 mm; 80% MVC: 0.30 1/100 mm 0.02 1/100 mm, ). Central aponeurosis length increased with contraction intensity (passive: 164.0 mm 5.4 mm; 80% MVC: 169.7 mm 5.8 mm), and aponeurosis width increased significantly (passive: 29.0 mm 1.2 mm; 80% MVC: 32.2 mm 1.3 mm, ). The integration of streamline-based fiber tracking with compartment-specific analysis reveals progressive architectural changes in the tibialis anterior during graded contractions. Compartment-specific differences in pennation angles and fiber shortening may suggest distinct functional roles, with implications for understanding muscle force production and clinical assessment.

Zusammenfassung

In this study, we investigate the mechanical elastic and failure behavior of porcine small intestinal walls (SIWs). In order to comprehensively examine the small intestine (SI) mechanically, all three sections of the SI, the duodenum, jejunum, and ileum, are examined. Single-edge notched tensile (SENT) experiments are performed on the entire wall structure as well as on the individual layers (serosal, muscular, and mucosal layer). In addition, the experiments are carried out in different loading directions (0°, 45°, and 90°) with respect to the tissue orientation. Overall, the elastic mechanical behavior for all regions and all layers is characterized by a typical, exponential, nonlinear behavior in combination with a partially distinct anisotropic behavior, featuring an broad elastic region of 1.1 to 1.7, with corresponding stresses of approximately 2 to 330 kPa. Failure behavior, as characterized by the critical energy release rate , exhibits obvious layer dependence. The average value of the mucosal layer is approximately four times higher than that of the muscular layer (1–2 N/mm), while the serosal layer has the highest values, reaching 6–10 N/mm. Additionally, the fracture behavior of the combined muscular and serosal layers of the duodenum, jejunum and ileum can be explained by classical laminate theory. However, the results of the entire wall indicate complicated interlayer behavior between the mucosal and muscular layers. Furthermore, the crack-tip tracking method and local deformation obtained from optical measurements help achieve a clearer understanding of crack initiation and propagation. These results provide a comprehensive dataset about the failure characteristics of the SI that can be used as input or for validating failure models in the future. Statement of Significance: This study is the first to report on experiments involving the failure of the porcine small intestine. The study investigates the region-, orientation-, and layer-specific mechanical properties of the small intestine in order to gain insight into its behavior under intact and failed conditions. Although layer-specific experimental studies are essential for a comprehensive understanding of small intestine function, they have received little attention to date. Additionally, this study examines crack propagation direction during uniaxial tensile tests. The study provides a unique database that improves our understanding of small intestine failure behavior and serves as a basis for corresponding models.

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BACKGROUND: Exercise intolerance, promoted by skeletal muscle- and mitochondrial dysfunction, has been identified as a therapeutic target in heart failure with preserved ejection fraction (HFpEF). In the context of mitochondrial dysfunction, altered cardiolipin integrity has been reported in the myocardium of HFpEF, suggesting Elamipretide, a cardiolipin stabilizing agent, as potential therapeutic approach. The present study investigated cardiolipin dysregulation in the skeletal muscle of HFpEF rats and analyzed the effect of Elamipretide treatment. METHODS: Female zucker fatty spontaneously hypertensive heart failure F1 hybrid lean (n=10, control) and obese rats (n=24, HFpEF) were included. At 20 weeks of age, HFpEF rats were randomized into 2 groups receiving NaCl (n=12) or Elamipretide (n=12) for 12 weeks. Skeletal muscle tissue was collected for whole-muscle force, single-fiber mechanics, mitochondrial respiration, histology and molecular analyses. RESULTS: HFpEF rats exhibited reduced cardiolipin levels (−6.8%, P=0.007) and maturation (shown via tafazzin expression), contractile dysfunction, titin hyperphosphorylation, fiber atrophy and increased oxidative stress markers. Elamipretide improved whole muscle (soleus: +8.2%, P=0.041, extensor digitorum longus: +10.9%, P=0.016) and single-fiber (soleus: +173.2%, P<0.001, extensor digitorum longus: +66.0%, P=ns) contractile function and titin phosphorylation (soleus: −35.4%, P<0.001, extensor digitorum longus: −40.2%, P<0.001), while preventing atrophy development (soleus: +49%, P=0.001, extensor digitorum longus: +54.8%, P<0.001). Improved mitochondrial function, presumably through cardiolipin-mediated improvements in oxidative phosphorylation, could be associated with muscle force and cardiolipin integrity. CONCLUSIONS: Our data highlight cardiolipin stabilization as a key modulator of mitochondrial and contractile function in HFpEF, identifying Elamipretide as a promising therapeutic approach for skeletal muscle dysfunction.

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Force generation dynamics in native muscle tissues have been stringently optimized by evolution. Realizing similar contractile dynamics in a widely available biomaterial and subsequently fabricating macroscopic functional modules from them remains challenging. Herein, we tailor two-photon stereolithography to 3D print synthetic muscles made from bovine serum albumin to realize 1 mm long contractile fibers. We show that pH-dependent contractions in these synthetic muscles follow parabolic force-length relationships similar to biological muscles. Achieved stress outputs of 0.78 ± 0.13 N cm−2 were within an order of magnitude of smooth and cardiac muscle. Stretch-shortening work loops performed under different strain rates in turn revealed a viscoelastic behavior and significant velocity dependence of work and net power, more similar to skeletal muscle. That an isotropic protein hydrogel can achieve such dynamics, reinforces the notion that these are not limited to sarcomere-level ordering and suggests a more general design space for non-canonical conformational dynamics to engineer performance improvements in artificial muscle materials.

Zusammenfassung

Smooth muscle (SM) exhibits rapid mechanical adaptation in response to various stimuli, posing challenges for reproducible experimental results and consistent material parameter determination in biomechanical modeling. Preconditioning involving repeated loading and unloading cycles are commonly used to stabilize mechanical responses prior to testing. However, their influence on tissue properties and data variability remains underexplored. This study compares the effects of three preconditioning routines – passive cycling (PCYC), no preconditioning (PNPC), and free contraction (PFC) – on the active and passive force responses of porcine urinary bladder (UB) SM tissue. Three tissue strips from 12 UBs were randomly assigned to one of the routines and underwent an identical protocol involving a passive stretch ramp and two isometric contractions (IC1, IC2) to evaluate active and passive force development. After PCYC, the tissue generated the highest active (IC2: 44.7 ± 29.4 kPa) and passive tensions (IC2: 5.6 ± 4.3 kPa), though it also showed the highest variance in active tension. PNPC resulted in the lowest variance in active tension with a coefficient of variation (CV) of 45%, and PFC showed the lowest variance in passive tension, CV = 57%. These findings imply that the decision for a certain preconditioning protocol influences the observed mechanical properties. In this context, PFC appears promising for minimizing passive force variability and preventing creep-induced lengthening. This could offer a more reliable foundation for subsequent experiments analyzing mechanical parameters. This study underscores the importance of customized preconditioning strategies to enhance consistency and comparability in SM research and organ modeling.

Zusammenfassung

Introduction: Active exoskeletons are increasingly used to reduce muscle activity and support lifting tasks. However, the effectiveness of exoskeletons can vary depending on the lifting technique. This study investigates the effects of a commercially available active exoskeleton (Apogee) on muscle activity during two different lifting techniques: stoop and squat.Methods: 17 healthy young adults (8 male, 9 female) participated in the study. Muscle activity was measured in the M. erector spinae (MES) and M. biceps femoris (MBF) using EMG while lifting a 15 kg box in four conditions: 1) without exoskeleton, 2) exoskeleton in passive mode, 3) 50% support and 20% counterforce, 4) 100% support and 60% counterforce.Results: The MBF activity was 29% lower during the squat technique compared to the stoop technique (F1,16 = 20.53, p < 0.01, ղP2 = 0.56). MES activity was similar across both techniques (F1,15 = 0.53, p = 0.48, ղP2 = 0.03). When pooling data across techniques, the exoskeleton significantly reduced MES (F1,45 = 18, p < 0.01, ղP2 = 0.53) and MBF activity (F1,48 = 10.2, p < 0.01, ղP2 = 0.39), with higher support levels leading to greater reductions in muscle activity. The stoop technique benefitted more from the exoskeleton, showing significant reductions in MES activity (10%–27% MVC) and MBF activity (7%–10% MVC). In contrast, squat lifting showed a significant reduction in MES (10%–17% MVC) activity but no significant reduction in MBF (2%–3% MVC) activity.Discussion: The results indicate that the exoskeleton provides greater benefits during the stoop technique, where the lifting motion primarily involves hip extension. The reduction in muscle activity supports the potential of exoskeletons in reducing muscle load and preventing work-related musculoskeletal disorders (MSDs). However, the squat technique showed limited improvements, suggesting that exoskeletons may need to be adapted for different lifting tasks. Future exoskeletons should aim to dynamically adjust their support based on the specific lifting technique to maximize effectiveness.

Zusammenfassung

Aponeuroses are thin, tendinous sheets that connect muscle bellies to tendons, playing a central role in force transmission. In order to improve the understanding of these mechanics, the present study examined the deformation of rabbit aponeuroses during passive muscle elongation and isometric and isotonic contractions against increasing forces. The strains of the aponeurosis from 99 isometric and isotonic muscle contractions were analysed in the rabbit gastrocnemius medialis (GASM) and plantaris (PLA) muscles, which have unipennate and multipennate fascicle architectures, respectively. Three-dimensional digital image correlation was employed to quantify aponeurosis strain between defined points along longitudinal and transverse paths on digitised muscle surfaces. Passive muscle elongation was characterised by longitudinal elongation and transverse narrowing, whereas muscle contraction generally resulted in longitudinal and transverse expansion of the aponeuroses. During isometric contraction, longitudinal strain ranged from 1% to 2%, whereas transverse strain averaged between 0% and 15%, depending on the muscle examined. Ultimately, active deformation exhibited a linear relationship between longitudinal aponeurosis strain and muscle force. The relative contributions of longitudinal and transverse deformation during passive and active states were muscle-specific. Together, these findings provide new insight on the shape change of aponeuroses and their interactions with the muscle tissue, while also providing indirect information on deformation patterns associated with force generation and transmission in pennate muscles.

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Stretch-shortening cycles (SSCs) enhance force and mechanical work compared with pure shortening contractions and are fundamental to locomotion. Although SSC mechanics are well studied, it remains unclear whether mechanical cycle-to-cycle carryover effects persist across repeated SSCs despite brief deactivation or inhibition of cross-bridge (XB) force production. To address this, single-skinned fibres from rat extensor digitorum longus muscles (n=21) underwent three consecutive SSCs at a slow velocity (1% maximal shortening velocity). Fibres were activated isometrically for 20s before SSC1, whereas SSC2 and SSC3 were each preceded by 4s of deactivation followed by 20s of isometric activation. Experiments were performed under control conditions and with Blebbistatin to inhibit XB force production. Repeated SSCs produced progressive performance enhancements under both conditions despite brief deactivation. From SSC1 to SSC3, peak force (Fpeak) increased by 14.6% and total SSC work (WorkSSC) by 50.1% under control conditions, and by 37.5% and 67.6%, respectively, with Blebbistatin. Increased short-range stiffness under control conditions suggests XB-mediated stretch resistance, whereas persistent increases during XB inhibition indicate contributions from non-XB structures, particularly titin. These findings support a sarcomeric memory effect that enhances stretch resistance and work during repeated SSCs.

Zusammenfassung

Eccentric muscle contractions are essential for locomotion and daily activities. Force during these contractions depends on both cross-bridge (XB) and non-cross-bridge (non-XB) elements, including titin, with contributions varying by fibre type and contraction velocity. Despite their importance, mechanisms of force generation during prolonged stretches remain unclear. Chemical XB inhibitors are commonly used to separate XB and non-XB contributions, but their effects have not been systematically compared under identical conditions. We measured eccentric force in single permeabilised fibres from fast-twitch rat extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles. Fibres were treated with blebbistatin (Bleb), 2,3-butanedione monoxime (BDM), or N-benzyl-p-toluene sulphonamide (BTS) and stretched from 0.85 to 1.3 times optimal length at three velocities (0.01, 0.1 and 1.0 maximal contraction velocity). XB inhibition produced fibre-type-dependent effects on early- and late-stretch force (slope1, slope2) and on end-of-stretch force (se). Stretch velocity and the type of XB inhibitor influenced se in both SOL and EDL fibres. However, in EDL fibres, se did not differ significantly between XB inhibitors and showed velocity-dependent effects under Bleb and BTS only, but not under BDM. Stretch-induced forces were less reduced than isometric forces, indicating substantial stretch-dependent non-XB contributions. These results show that eccentric force arises from coordinated XB and non-XB mechanisms in a fibre-type-dependent manner and highlight Bleb as an effective tool for probing these contributions.

Zusammenfassung

The stomach is a hollow organ within the gastrointestinal tract that plays a central role in the breakdown of ingested food. Its secretion of gastric acid facilitates chemical digestion, while the contraction of its smooth muscle aids in mechanical digestion. The upper, cranial part of the stomach acts as a reservoir for ingested food, while the lower, caudal part grinds the food through peristaltic contractions. Understanding the mechanical properties of the stomach is critical to gaining insight into its function and the overall digestive process. In this study, we performed equibiaxial tensile tests on porcine stomach tissue samples (n = 28) from the fundus, representing the cranial area, and the corpus, representing the central area. We analyzed the passive and active stress-stretch relationship as well as the force-velocity relationship. The main findings of our experiments are: (1) fundus samples show more isotropic mechanical properties, i.e., similar stress-stretch and force-velocity relationships in both directions (longitudinal vs. circumferential), (2) corpus samples show more anisotropic mechanical properties, i.e., there are direction-dependent differences in optimal stretch, maximal stress and the maximal shortening velocity, and (3) the corpus is much stiffer than the fundus. This study is the first to use biaxial tensile experiments to determine the active stress-stretch relationship in stomach smooth muscle and the first to characterize the biaxial force-velocity relationship in smooth muscle in general. The data provided advance our understanding of both smooth muscle and organ-level mechanics and provide more comprehensive insights than existing uniaxial tests in the literature. These findings are critical for the development and validation of constitutive muscle models that can predict stomach function in health and disease.

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Background Rowing combines on-water and ergometer-based training, while inertial measurement units (IMUs) offer a practical approach for field-based biomechanical monitoring. This study examined whether trunk-mounted IMU data can distinguish static Concept2 (C2), dynamic RP3, and on-water rowing conditions. Methods Ten youth rowers (16.3 ± 0.8 years) performed high-intensity rowing in all three conditions. Triaxial acceleration and gyroscope data were recorded at 208 Hz. Six classical machine-learning and four deep-learning models classified overlapping three-stroke windows using leave-one-subject-out cross-validation. Repeated-measures analyses assessed condition-specific IMU magnitude features. Results The ensemble achieved the highest mean accuracy (85.5 ± 10.3%). Individual accuracy varied from 24.0% to 97.1% across models and athletes. The 7,545 windows were imbalanced toward Boat, with a no-information rate of 71.8%. Boat was identified most reliably, whereas RP3 was frequently misclassified as Boat. Nine of ten magnitude features remained significant after false-discovery-rate correction. Conclusions Trunk-mounted IMU signals distinguished the three rowing conditions at group level. However, class imbalance, RP3 familiarity, measurement order, boat-standardisation asymmetry, and athlete-level variability require cautious interpretation. Applied use requires athlete-specific calibration and prospective validation.

Zusammenfassung

Hemolymph channels (lacunae) in the legs of spiders are part of their open circulatory system. They are defined as hemolymph-filled spaces between tissues within the exoskeletal tubes of the legs which are otherwise largely filled with muscles. In two of the major leg joints, the leg segments are connected via hinge joints with axes that are located at their dorsal rims. The lacunae are used to channel hemolymph, which acts as a hydraulic fluid, to the extensor-less joints during the extension of the legs. However, due to competing optimization criteria of muscle-driven flexion and drainage of the hemolymph, fluid drag in the lacunae may hinder movement and force generation during flexion. Numerical modelling of dynamic flexions of the tibia-metatarsus joint, considering anatomical and physiological properties identified in the hunting spider Cupiennius salei, was used to investigate the trade-off between muscular force and hemolymph-drainage. The results showed that the diameters of the hemolymph channels exhibit a broad optimum for quick flexion. Within a wide range of channel diameters flexion times are hardly affected. Muscle properties, especially the time of muscle activation, strongly dampen the effect of the reduced muscle cross-section available. With small loads of 0.1 g, similar to the spiders’ common prey size, the radius of the observed effective lacunae seems to enable the fastest flexions. A change in the aspect ratio of the tibia while maintaining the proportionality of its radius and the radius of the effective hemolymph channels leads to an extension of the flexion time.

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The endomysium, the innermost layer of the extracellular matrix (ECM), was shown to play an important role in both passive and active force transmission. However, its mechanical contribution within muscle fiber bundles remains incompletely understood. We hypothesized that dissecting one of the endomysial connections within a fiber bundle would alter force production and lead to changes in sarcomere lengths and their heterogeneity. Muscle fiber bundles (n = 12) were extracted from the extensor digitorum longus muscles of rats and chemically skinned. Their passive and active stress-length relationships were measured under two conditions: (i) with intact endomysium and (ii) after blunt dissection of endomysial connections between two adjacent peripheral fibers. Disruption of endomysial continuity significantly reduced passive stress by 26.5 % (p < 0.01) and active stress by 21.9 % (p < 0.001) on average across all lengths tested. It also shifted the optimal fiber length (Lopt) to longer values by 6.2 % (p < 0.01). Despite these mechanical changes, average sarcomere lengths (along fibers) and their heterogeneity remained unchanged. Length heterogeneity was only observed at a longer fiber length (1.3 Lopt) in the passive state before dissection. These findings demonstrate that endomysial connections are integral to the mechanical behavior of muscle fiber bundles, influencing both passive and active stress. The absence of sarcomere length changes along fibers suggests that other microstructural mechanisms, such as altered lattice spacing or impaired lateral force transmission, may underlie the observed changes. These results highlight the importance of ECM integrity in muscle mechanics and have implications for orthopedic interventions and neuromuscular disorder management.

Zusammenfassung

Introduction: Musculoskeletal disorders (MSDs), especially lower back pain, are common consequences of repetitive and long-term mechanical stress. Exoskeletons offer a promising approach to reduce this stress by supporting the wearer during physical labour. This study investigated the effect of an active exoskeleton (Apogee) on muscle activation and joint kinematics during load lifting at different lifting speeds and exoskeleton support levels. Methods: Sixteen healthy young adults (8 male, 8 female) lifted a 15 kg box at two lifting speeds (9 and 12 lifting cycles/min) and four support levels: 1) without exoskeleton, 2) exoskeleton in passive mode, 3) 50% support and 20% counterforce, 4) 100% support and 60% counterforce. Muscle activity was measured in the M. erector spinae (MES), M. biceps femoris (MBF) and M. vastus medialis (MVM) using EMG. Furthermore, joint range of motion (ROM) in the ankle, knee and hip were analysed using 3D motion capture. Results: Faster lifting significantly (p < 0.05) increased MBF (by 4.0% ± 1.5% maximum voluntary contraction, MVC) and MVM (1.6% ± 0.7% MVC) activity, while MES remained unaffected. The highest support level led to a significant decrease in MES and MBF activity by about 22.3% MVC and 10.6% MVC, respectively, as well as a small increase in hip joint ROM by 6° compared to lifting without exoskeleton support. There was no interaction between the level of support and lifting speed. Discussion: The decrease in MES activity of 22.3% MVC with full support suggests a potent reduction in spinal load. MBF activity increased less with higher speeds when support was applied. The MVM showed low and stable activity across all conditions. These findings suggest that the active exoskeleton Apogee provides support regardless of lifting speed and may help prevent MSDs in occupational settings. Users can adjust support levels based on task requirements and personal comfort.

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Animals utilize elastic tendons in their limbs to store and release energy, reducing muscle effort and overall energy expenditure. At the same time, they navigate rough terrain dynamically without falling, despite significant neural delays. This ability allows them to achieve both robust and energy-efficient locomotion simultaneously—two properties often considered trade-offs in robotics. Through computational simulations, this study demonstrates how muscle–tendon mechanics can facilitate both energy-efficient and robust locomotion during perturbed vertical hopping across different muscle–tendon length configurations. Integrating muscle–tendon-like viscoelastic materials into legged robots may offer a solution to the previously perceived trade-off.

Zusammenfassung

Our main finding was that the stretch–shortening cycle (SSC) effect was not associated with cortical or spinal excitability modulations, and the main criticism of Taube et al. (2025) was that this main finding should not be generalised to all SSCs. This criticism appears misplaced as we never generalised our main finding to other SSCs and actually explicitly stated as part of our limitations that the ‘results are specific to our set-up’ and also ‘specific to the controlled dynamometer conditions used’ (Rissmann et al., 2025). Obviously, a different set-up or different stretch or shortening parameters could lead to diverging findings because of altered activation, muscle and muscle–tendon unit (MTU) dynamics, and we even stated that our findings do ‘not preclude cortical and spinal excitability modulations during other SSC conditions’. As such, we did not feel it necessary to end our article's title with a statement on generalisability. Accordingly, we strongly disagree with Taube et al. (2025) that our interpretation of our results is misleading.

Zusammenfassung

In order to meet the requirements of body weight and height and the associated changing tasks and movement patterns during the growth of living bodies, significant changes in the skeletal musculature occur during this phase. In this study, the age-dependent (between 21 and 100 days) mechanical and microstructural tissue behaviour of the calf musculature, consisting of soleus muscles (SOL), gastrocnemius muscles (GAS) and plantaris muscles (PLA), was examined. To this end, cubic muscle tissue samples were examined using axial and semi-confined compression experiments. In addition, the essential muscle tissue components (muscle fibres, extracellular matrix, remaining components) were analysed. In a final step, these results were linked to morphological properties of the animals and muscles (animal mass, muscle mass, tibia length). Interestingly, the mechanical properties of the individual muscle types hardly differ from each other during growth, while both the morphological and microstructural properties change significantly. Thus, a clear increase of all morphological parameters (animal mass by 850%, muscle mass by 1000% (SOL), 1183% (GAS) and 1050% (PLA), tibia length by 235%) can be seen. In comparison, the microstructural parameters show a less consistent trend. The proportion of muscle fibres in the tissue cross-section increases by about 138% in the SOL, whereas the fibre proportion in both the GAS and PLA increases by only 109%. Consequently, the ECM proportion in the tissue cross-section decreases by 48%, 58% and 52% for SOL, GAS and PLA. Overall, the data obtained her e provides a deeper understanding of muscle growth and, in particular, of different muscle types that have different functions inside the calf. On the other hand, these data represent a good and comprehensive basis for later model developments.

Zusammenfassung

It is unclear whether cortical and spinal excitability modulations contribute to enhanced stretch–shortening cycle (SSC) performance. Therefore, this study investigated cortical and spinal excitability modulations during and following shortening of SSC contractions compared with pure shortening (SHO) contractions. Participants (n = 18) performed submaximal voluntary plantar flexion contractions while prone on the dynamometer bench. The right foot was strapped onto the dynamometer's footplate attachment, and the resultant ankle joint torque and crank arm angle were recorded. Cortical and spinal excitability modulations of the soleus muscle were analysed by eliciting compound muscle actional potentials via electrical nerve stimulation, cervicomedullary motor-evoked potentials (CMEPs) via electrical stimulation of the spinal cord, and motor-evoked potentials (MEPs) via magnetic stimulation of the motor cortex. Mean torque following stretch was significantly increased by 7 ± 3% (P = 0.029) compared with the fixed-end reference (REF) contraction, and mean torque during shortening of SSC compared with SHO was significantly increased by 12 ± 24% (P = 0.046). Mean steady-state torque was significantly lower by 13 ± 3% (P = 0.006) and 9 ± 12% (P = 0.011) following SSC compared with REF and SHO, respectively. Mean steady-state torque was not significantly different following SHO compared with REF (7 ± 8%, P = 0.456). CMEPs and MEPs were also not significantly different during shortening of SSC compared with SHO (P ≥ 0.885) or during the steady state of SSC, SHO and REF (P ≥ 0.727). Therefore, our results indicate that SSC performance was not associated with cortical or spinal excitability modulations during or after shortening, but rather driven by mechanical mechanisms triggered during active stretch.

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Purpose: Pedobarography is frequently employed for the identification and characterisation of foot pathologies in paediatrics. However, the lack of standardised normalisation methods presents a challenge for cross-age comparisons. This cross-sectional study provides normative plantar pressure data for typically developing children aged 4–17 years and compares normalisations and explanatory powers of parameters measuring peak and total load. Methods: Dynamic foot pressure of 101 typically developing children aged 4–17 years was measured at self-selected speed using the mid-gait protocol. They were divided into five age groups: 4–6, 7–8, 9–11, 12–14 and 15–17 years old. Force and pressure variables measuring peak and total load were normalised by body weight or scaled by maximum value and the foot region where the peak pressure occurred was identified. Results: The absolute values demonstrated an increase in load with advancing age. In contrast, when normalised to body weight, peak pressure and pressure time integrals decreased. The scaled peak pressure showed a load shift to the forefoot. The results indicate that the normalised parameters exhibit superior qualitative significance, suggesting a more dynamic gait pattern and improved morphology of the foot in relation to body weight with increasing age. Conclusions: This study shows that standardisation of the measurement protocol is imperative because results in typically developing children can vary depending up parameter selection and normalisation technique. Level of evidence: 3

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Mechanical organ models are crucial for understanding organ function and clinical applications. These models rely on input data regarding smooth muscle properties, typically gathered from experiments involving stimulations at different muscle lengths. However, reproducibility of these experimental results is a major challenge due to rapid changes in active and passive smooth muscle properties during the measurement period. Usually, preconditioning of the tissue is employed to ensure reproducible behavior in subsequent experiments, but this process itself alters the tissue's mechanical properties. To address this issue, three protocols (P1, P2, P3) without preconditioning were developed and compared to preserve the initial mechanical properties of smooth muscle tissue. Each protocol included five repetitive experimental cycles with stimulations at a long muscle length, varying in the number of stimulations at a short muscle length (P1: 0, P2: 1, P3: 2 stimulations). Results showed that P2 and P3 successfully reproduced the initial active force at a long length over five cycles, but failed to maintain the initial passive forces. Conversely, P1 was most effective in maintaining constant passive forces over the cycles. These findings are supported by existing adaptation models. Active force changes are primarily due to the addition or removal of contractile units in the contractile apparatus, while passive force changes mainly result from actin polymerization induced by contractions, leading to cytoskeletal stiffening. This study introduces a new method for obtaining reproducible smooth muscle parameters, offering a foundation for future research to replicate the mechanical properties of smooth muscle tissue without preconditioning.

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AbstractThe maintenance of an appropriate ratio of body fat to muscle mass is essentialfor the preservation of health and performance, as excessive body fat is associatedwith an increased risk of various diseases. Accurate body composition assessmentrequires precise segmentation of structures. In this study we developed a novelautomatic machine learning approach for volumetric segmentation and quantita-tive assessment of MRI volumes and investigated the efficacy of using a machinelearning algorithm to assess muscle, subcutaneous adipose tissue (SAT), and bonevolume of the thigh before and after a strength training. Eighteen healthy, young,female volunteers were randomly allocated to two groups: intervention group(IG) and control group (CG). The IG group followed an 8-week strength endur-ance training plan that was conducted two times per week. Before and after thetraining, the subjects of both groups underwent MRI scanning. The evaluation ofthe image data was performed by a machine learning system which is based ona 3D U-Net- based Convolutional Neural Network. The volumes of muscle, bone,and SAT were each examined using a 2 (GROUP IG vs. CG) × 2 (TIME pre-intervention vs. post-intervention) analysis of variance (ANOVA) with repeatedmeasures for the factor TIME. The results of the ANOVA demonstrate significantTIME × GROUP interaction effects for the muscle volume (F1,16 = 12.80, p = 0.003,ηP2 = 0.44) with an increase of 2.93% in the IG group and no change in the CG(−0.62%, p = 0.893). There were no significant changes in bone or SAT volumebetween the groups. This study supports the use of artificial intelligence systemsto analyze MRI images as a reliable tool for monitoring training responses onbody composition.

Zusammenfassung

In their physiological condition, muscles are surrounded by connective tissue, other muscles and bone. These tissues exert transverse forces that change the three-dimensional shape of the muscle compared to its isolated condition, in which all surrounding tissues are removed. A change in shape affects the architecture of a muscle and therefore its mechanical properties. The rabbit M. plantaris is a multi-pennate calf muscle consisting of two compartments. A smaller, bi-pennate inner muscle compartment is embedded in a larger, uni-pennate outer compartment (Böl et al., 2015). As part of the calf, the plantaris is tightly packed between other muscles. It is unclear how packing affects the shape and architecture of the plantaris. Therefore, we examined the isolated and packed plantaris of the contralateral legs of three rabbits to determine the influence of the surrounding muscles on its shape and architectural properties using photogrammetric reconstruction and manual digitization, respectively. In the packed condition, the plantaris showed a 27% increase in fascicle pennation and a 54% increase in fascicle curvature compared to the isolated condition. Fascicle length was not affected by muscle packing. The change in muscle architecture occurred mainly in the outer compartment of the plantaris. Furthermore, the isolated plantaris showed a more circular shape and a reduced width of its muscle belly. It can be concluded that the packed plantaris is flattened by the forces exerted by the surrounding muscles, causing a complex architectural change. The data provided improve our understanding of muscle packages in general and can be used to develop and validate realistic three-dimensional muscle models.

Zusammenfassung

During the shortening of stretch-shortening cycles (SSCs), muscle force output is enhanced compared with pure shortening (SHO), referred to as the SSC-effect. In general, muscle-tendon unit (MTU), muscle belly, muscle fascicle, and tendon length changes can be decoupled during contraction, which affects force generation and elastic recoil. We researched whether MTU decoupling contributes to the SSC-effect. Participants performed electrically stimulated submaximal fixed-end, SSC, and SHO plantar-flexions on a dynamometer at two velocities (40, 120°/s) and two ranges of motion (15, 25°). Fascicle and tendon length changes of the gastrocnemius medialis, and ankle joint kinematics were assessed by ultrasound and motion capture, respectively. During SSC shortening, ankle joint torque and work, MTU force and work, and fascicle force were increased by 12%–22% compared with SHO, confirming a SSC-effect. Further, fascicle length change and velocity during SSCs were significantly reduced compared with SHO condition, and SSC fascicle work was decreased by ~35%. Our results indicate that MTU decoupling leads to a reduction in fascicle shortening amplitude and velocity, thereby increasing the muscle's force capacity while reducing its work output during SSC shortening. MTU decoupling therefore contributes to the SSC-effect and underlines the limited transferability of joint work measurements to estimated muscle work.

Zusammenfassung

The urinary bladder is a hollow organ that undergoes significant deformation as it receives, stores, and releases urine. To understand the organ mechanics, it is necessary to obtain information about the material properties of the tissues involved. In displacement-controlled tensile tests, tissue samples are mounted on a device that applies stretches to the tissue in one or more directions, resulting in a specific stress response. For this study, we performed uniaxial and biaxial stretch experiments on tissue samples (n = 36) from the body region of the porcine urinary bladder. We analyzed the stress-relaxation, activation dynamics, and passive and active stretch-stress response. Main findings of our experiments are: (1) For uniaxial and biaxial stretching, the time constants for stress-relaxation depend on the stretch amplitude, (2) biaxially stretched samples experienced slower activation with increasing by 163% compared to uniaxial stretching, (3) biaxial tests are characterized by reduced optimum stretches by -18%, and (4) biaxial and uniaxial tests showed no significant difference in maximum active stresses To interpret the results, we present a continuum mechanical model based on a viscoelastic, isotropic solid extended by a set of active muscle fibers. Model predictions show that results (3) and (4) can be explained by a uniform distribution of fiber orientations and a specific shape of the active fiber stress-stretch relationship. This study highlights how deformation modes during tensile testing affects smooth muscle mechanics, proving insights for interpreting experimental data and improving organ modeling.

Zusammenfassung

Measurement of hip external rotation strength (ERS) is important for preventive and rehabilitative purposes. ERS can be measured in 3 different positions in the isokinetic dynamometer ISOMED2000. However, it is not clear whether these measurement positions effect ERS nor if these positions are reliable in the ISOMED2000. Hence, the purpose of this study was to compare ERS in these positions, the reliability and the agreement. A cross-sectional design was conducted to compare measurement positions and a test–retest design to assess intra-rater reliability and agreement. Twenty-four healthy, physically active athletes participated in the study. Peak isometric torque was measured in the ISOMED in prone, supine, and side-lying position across two sessions on one day. Differences between positions were evaluated with the Wilcoxon-signed-rank test and cliff’s delta. Reliability was assessed via intraclass correlation. Agreement was determined using the standard error of measurement (SEM), minimal detectable change (MDC), and Bland-Altman analysis (BAA). Results indicated a significant influence of measurement position on ERS (p < 0.001) with high effect sizes (>0.74). Reliability and agreement were high in all positions, but highest for the side-lying position (ICC = 0.90 0.78, 0.96; SEM = 0.08; MDC = 0.23; BAA_bias = 3.4 %, BAA_loA = 37 %). There were only poor to moderate correlations between measurement positions. These findings suggest that measurement position significantly affects ERS. Furthermore, the effect varies across individuals indicating that normative values cannot be used interchangeably or be adapted across positions. In diagnostic testing ERS should be measured in the same position, but preferably in the side-lying position.

Zusammenfassung

Three-dimensional (3D) marker-based motion capture is the current gold standard to assess and monitor pathological gait in a clinical setting. However, 3D markerless motion capture based on pose estimation is advancing into the field of gait analysis. This study aims at evaluating the lower-body 3D gait kinematics and kinetics from synchronously recorded Theia3D markerless and CAST marker-based systems. Twelve healthy individuals and 34 clinical patients aged 8–61 years walked at self-selected speed over a 13 m long walkway. Similarity between models was statistically analysed using inter-trial variability, root mean square error, Pearson’s correlation coefficient and Statistical Parametric Mapping. Inter-trial variability was on average higher for clinical patients in both models. Overall, the markerless system demonstrated similar gait patterns although hip and knee rotations were non-comparable. Pelvic anterior tilt was significantly underestimated. Significant differences especially in peak values at specific phases of the gait cycle were observed across all planes for all joints (more so for clinical patients than healthy subjects) as well as in the sagittal powers of the hip, knee and ankle. Theia3D markerless system offers great potential in gait analysis. This study brings awareness to potential clinical users and researchers where they can have confidence, as well as areas where caution should be exercised.

Zusammenfassung

During muscle contraction, not only are the fascicles shortening but also the pennation angle changes, which leads to a faster contraction of the muscle than of its fascicles. This phenomenon is called muscle gearing, and it has a direct influence on the force output of the muscle. There are few studies showing pennation angle changes during isometric and concentric contractions for different contraction intensities and muscle lengths. Therefore, the aim was to determine these influences over a wide range of contraction intensities and ankle joint angles for human triceps surae. Additionally, the influence of contraction intensity and ankle joint angle on muscle gearing was evaluated. Ten sport students performed concentric and isometric contractions with intensities between 0 and 90\% of the maximum voluntary contraction and ankle joint angles from 50° to 120°. During these contractions, the m. gastrocnemius medialis and lateralis and the m. soleus were recorded via ultrasound imaging. A nonlinear relationship between fascicle length and pennation angle was discovered, which can be described with a quadratic fit for each of the muscles during isometric contraction. A nearly identical relationship was detected during dynamic contraction. The muscle gearing increased almost linearly with contraction intensity and ankle joint angle.

Zusammenfassung

Digital human body models are used to simulate injuries that occur as a result of vehicle collisions, vibration, sports, and falls. Given enough time the body’s musculature can generate force, affect the body’s movements, and change the risk of some injuries. The finite-element code LS-DYNA is often used to simulate the movements and injuries sustained by the digital human body models as a result of an accident. In this work, we evaluate the accuracy of the three muscle models in LS-DYNA (MAT_156, EHTM, and the VEXAT) when simulating a range of experiments performed on isolated muscle: force-length-velocity experiments on maximally and sub-maximally stimulated muscle, active-lengthening experiments, and vibration experiments. The force-length-velocity experiments are included because these conditions are typical of the muscle activity that precedes an accident, while the active-lengthening and vibration experiments mimic conditions that can cause injury. The three models perform similarly during the maximally and sub-maximally activated force-length-velocity experiments, but noticeably differ in response to the active-lengthening and vibration experiments. The VEXAT model is able to generate the enhanced forces of biological muscle during active lengthening, while both the MAT_156 and EHTM produce too little force. In response to vibration, the stiffness and damping of the VEXAT model closely follows the experimental data while the MAT_156 and EHTM models differ substantially. The accuracy of the VEXAT model comes from two additional mechanical structures that are missing in the MAT_156 and EHTM models: viscoelastic cross-bridges, and an active titin filament. To help others build on our work we have made our simulation code publicly available.

Zusammenfassung

Stretch-shortening cycles (SSCs) involve muscle lengthening (eccentric contractions) instantly followed by shortening (concentric contractions). This combination enhances force, work, and power output compared to pure shortening (SHO), which is known as SSC-effect. Recent evidence indicates both cross-bridge-based (XB) and non-cross-bridge-based (non-XB, e.g., titin) structures contribute to this effect. This study analyzed force re-development following SSCs and SHO to gain further insight into the roles of XB and non-XB structures regarding the SSC-effect. Experiments were conducted on rat soleus muscle fibres (n=16) with different SSC velocities (30%, 60%, 85% of maximum shortening velocity) and constant stretch-shortening magnitudes (18% of optimum length). The XB inhibitor blebbistatin was used to distinguish between XB and non-XB contributions to force generation. Results showed SSCs led to significantly greater (1.02±.15 vs. 0.68±.09 ΔF/Δt; t(62)=8.61, p<.001, d=2.79) and faster (75 ms vs. 205 ms; t(62) = -6.37, p<.001, d=-1.48) force re-development compared to SHO in the control treatment. In the blebbistatin treatment, SSCs still resulted in greater (.11±.03 vs. .06±.01 ΔF/Δt; t(62) = 8.00, p<.001, d=2.24) and faster (3010±1631 vs. 7916±3230 ms; t(62) = -8.00, p<.001, d=-1.92) force re-development compared to SHO. These findings deepen our understanding of the SSC-effect, underscoring the involvement of non-XB structures like titin in modulating force production. This modulation likely involves complex mechanosensory coupling from stretch to signal transmission during muscle contraction.

Zusammenfassung

After an initial increase, isovelocity elongation of a muscle fiber can lead to diminishing (referred to as Give in the literature) and subsequently increasing force. How the stretch velocity affects this behavior in slow-twitch fibers remains largely unexplored. Here, we stretched fully activated individual rat soleus muscle fibers from 0.85 to 1.3 optimal fiber length at stretch velocities of 0.01, 0.1, and 1 maximum shortening velocity, vmax, and compared the results with those of rat EDL fast-twitch fibers obtained in similar experimental conditions. In soleus muscle fibers, Give was 7\%, 18\%, and 44\% of maximum isometric force for 0.01, 0.1, and 1 vmax, respectively. As in EDL fibers, the force increased nearly linearly in the second half of the stretch, although the number of crossbridges decreased, and its slope increased with stretch velocity. Our findings are consistent with the concept of a forceful detachment and subsequent crossbridge reattachment in the stretch's first phase and a strong viscoelastic titin contribution to fiber force in the second phase of the stretch. Interestingly, we found interaction effects of stretch velocity and fiber type on force parameters in both stretch phases, hinting at fiber type-specific differences in crossbridge and titin contributions to eccentric force. Whether fiber type-specific combined XB and non-XB models can explain these effects or if they hint at some not fully understood properties of muscle contraction remains to be shown. These results may stimulate new optimization perspectives in sports training and provide a better understanding of structure--function relations of muscle proteins.

Zusammenfassung

Purpose: In this paper, we introduce a novel method for determining 3D deformations of the human tibialis anterior (TA) muscle during dynamic movements using 3D ultrasound. Materials and Methods: An existing automated 3D ultrasound system is used for data acquisition, which consists of three moveable axes, along which the probe can move. While the subjects perform continuous plantar- and dorsiflexion movements in two different controlled velocities, the ultrasound probe sweeps cyclically from the ankle to the knee along the anterior shin. The ankle joint angle can be determined using reflective motion capture markers. Since we considered the movement direction of the foot, i.e., active or passive TA, four conditions occur: slow active, slow passive, fast active, fast passive. By employing an algorithm which defines ankle joint angle intervals, i.e., intervals of range of motion (ROM), 3D images of the volumes during movement can be reconstructed. Results: We found constant muscle volumes between different muscle lengths, i.e., ROM intervals. The results show an increase in mean cross-sectional area (CSA) for TA muscle shortening. Furthermore, a shift in maximum CSA towards the proximal side of the muscle could be observed for muscle shortening. We found significantly different maximum CSA values between the fast active and all other conditions, which might be caused by higher muscle activation due to the faster velocity. Conclusion: In summary, we present a method for determining muscle volume deformation during dynamic contraction using ultrasound, which will enable future empirical studies and 3D computational models of skeletal muscles.

Zusammenfassung

Stretch-shortening cycles (SSCs) outperform shortening contractions preceded by isometric contractions in terms of enhanced force/torque, work, and power production during shortening. This so-called SSC-effect is presumably related to the active muscle stretch before shortening in SSCs. However, it remains unclear whether the stretch-induced higher preload level or stretch-induced history dependence effects maximize the SSC-effect. Therefore, we analyzed fascicle behavior, MTU shortening work, and torque/force (N=12 participants) via ultrasound and dynamometry during electrically stimulated submaximal plantar flexion contractions from 10° plantarflexion to 15° dorsiflexion. To elucidate the effects of preload level and preload modality (i.e. contraction type) on shortening performance, muscle-tendon unit shortening was preceded by fixed-end (SHO), active stretch (SSC), and preload-matched fixed-end (MATCHED) contractions. Prior to shortening MATCHED and SCC had the same preload level (1% torque difference), similar joint position and muscle fascicle lengths. Compared with SHO, shortening work was significantly (p<.001, partial η2=.749) increased by 85% and 55% for SSC and MATCHED, respectively, with SSC shortening work being significantly higher than MATCHED (p=.016). This indicates that preload contributes by 65% to the overall SSC-effect, so that 35 % need to be referred to stretched-induced history dependent mechanisms. Additionally, SSC showed larger fascicle forces at the end of shortening (p<.001) and 20% less depressed isometric torque following shortening compared with MATCHED (p<.001). Since potential decoupling effects by the series elastic element were controlled by matching the preload levels, we conclude that the difference between SSC and MATCHED is related to stretch-induced long-lasting history dependent effects.

Zusammenfassung

Muscles and muscle fibers are volume-constant constructs that deform when contracted and develop internal pressures. However, muscles embedded in hydrostatic skeletons are also exposed to external pressures generated by their activity. For two examples, the pressure generation in spiders and in annelids, we used simplified biomechanical models to demonstrate that high intracellular pressures diminishing the resulting tensile stress of the muscle fibers are avoided in the hydrostatic skeleton. The findings are relevant for a better understanding of the design and functionality of biological hydrostatic skeletons.

Zusammenfassung

Connective tissues can be recognized as an important structural support element in muscles. Recent studies have also highlighted its importance in active force generation and transmission between muscles, particularly through the epimysium. In the present study, we aimed to investigate the impact of the endomysium, the connective tissue surrounding muscle fibers, on both passive and active force production. Pairs of skeletal muscle fibers were extracted from the extensor digitorum longus muscles of rats and, after chemical skinning, their passive and active force–length relationships were measured under two conditions: (i) with the endomysium between muscle fibers intact, and (ii) after its dissection. We found that the dissection of the endomysium caused force to significantly decrease in both active (by 22.2 % when normalized to the maximum isometric force; p < 0.001) and passive conditions (by 25.9 % when normalized to the maximum isometric force; p = 0.034). These findings indicate that the absence of endomysium compromises muscle fiber’s not only passive but also active force production. This effect may be attributed to increased heterogeneity in sarcomere lengths, enhanced lattice spacing between myofilaments, or a diminished role of trans-sarcolemmal proteins due to dissecting the endomysium. Future investigations into the underlying mechanisms and their implications for various extracellular matrix-related diseases are warranted.

Zusammenfassung

As part of the digestive system, the stomach plays a crucial role in the health and well-being of an organism. It produces acids and performs contractions that initiate the digestive process and begin the break-up of ingested food. Therefore, its mechanical properties are of interest. This study includes a detailed investigation of strains in the porcine stomach wall during passive organ filling. In addition, the observed strains were applied to tissue samples subjected to biaxial tensile tests. The results show inhomogeneous strains during filling, which tend to be higher in the circumferential direction (antrum: 13.2%, corpus: 22.0%, fundus: 67.8%), compared to the longitudinal direction (antrum: 4.8%, corpus: 24.7%, fundus: 50.0%) at a maximum filling of 3500 ml. Consequently, the fundus region experienced the greatest strain. In the biaxial tensile experiments, the corpus region appeared to be the stiffest, reaching nominal stress values above 400 kPa in the circumferential direction, whereas the other regions only reached stress levels of below 50 kPa in both directions for the investigated stretch range. Our findings gain new insight into stomach mechanics and provide valuable data for the development and validation of computational stomach models.

Zusammenfassung

Background: Joint range of motion based on the neutral null method, muscle strength based on manual muscle testing, and selective voluntary motor control based on selective control assessment of the lower extremity are standard parameters of a pediatric three-dimensional clinical gait analysis. Lower-limb reference data of children are necessary to identify and quantify abnormalities, but these are limited and when present restricted to specific joints or muscles. Methods: This is the first study that encompasses the aforementioned parameters from a single group of 34 typically developing children aged 5–17 years. Left and right values were averaged for each participant, and then the mean and standard deviation calculated for the entire sample. The data set was tested for statistical significance (p < 0.05). Results: Joint angle reference values are mostly consistent with previously published standards, although there is a large variability in the existing literature. All muscle strength distributions, except for M. quadriceps femoris, differ significantly from the maximum value of 5. The mean number of repetitions of heel-rise test is 12 ± 5. Selective voluntary motor control shows that all distributions, except for M. quadriceps femoris, differ significantly from the maximum value of 2. Conclusion: Since typically developing children do not match expectations and reference values from the available literature and clinical use, this study emphasizes the importance of normative data. Excessively high expectations lead to typically developing children being falsely underestimated and affected children being rated too low. This is of great relevance for therapists and clinicians.

Zusammenfassung

The function of a muscle is highly dependent on its architecture, which is characterized by the length, pennation, and curvature of the fascicles, and the geometry of the aponeuroses. During in vivo function, muscles regularly undergo changes in length, thereby altering their architecture. During passive muscle lengthening, fascicle length (FL) generally increases and the angle of fascicle pennation (FP) and the fascicle curvature (FC) decrease, while the aponeuroses increase in length but decrease in width. Muscles are differently structured, making their change during muscle lengthening complex and multifaceted. To obtain comprehensive data on architectural changes in muscles during passive length, the present study determined the three-dimensional fascicle geometry of rabbit M. gastrocnemius medialis (GM), M. gastrocnemius lateralis (GL), and M. plantaris (PLA). For this purpose, the left and right legs of three rabbits were histologically fixed at targeted ankle joint angles of 95° (short muscle length SML) and 60° (long muscle length LML), respectively, and the fascicles were tracked by manual three-dimensional digitization. In a second set of experiments, the GM aponeurosis dimensions of ten legs from five rabbits were determined at varying muscle lengths via optical marker tracking. The GM consisted of a uni-pennated compartment, whereas the GL and PLA contained multiple compartments of differently pennated fascicles. In the LML compared to the SML, the GM, GL, and PLA had on average a 41%, 29%, and 41% increased fascicle length, and a 30%, 25%, and 33% decrease in fascicle pennation and a 32%, 11%, and 35% decrease in fascicle curvature, respectively. Architectural properties were also differentiated among the different compartments of the PLA and GL, allowing for a more detailed description of their fascicle structure and changes. It was shown that the compartments change differently with muscle length. It was also shown that for each degree of ankle joint angle reduction, the proximal GM aponeurosis length increased by 0.11%, the aponeurosis width decreased by 0.22%, and the area was decreased by 0.20%. The data provided improve our understanding of muscles and can be used to develop and validate muscle models.

Zusammenfassung

Occupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational platform motion. Kinematics of seventeen healthy subjects was tracked using 3D motion capturing. Surface electromyography were used to quantify muscle activity of left and right sternocleidomastoideus (SCM) and trapezius (TRP) muscles. The results show clear evidence that rotated head postures affect the static as well as the dynamic behavior of muscle activity during the virtual braking event. With head turned to the right, the contralateral left muscles yielded higher base activation and delayed muscle onset times. In contrast, right muscles had much lower activations and showed no relevant changes in muscle activation between nominal and rotated head position. The observed delayed muscle onset times and increased asymmetrical muscle activation patterns in the rotated head position are assumed to affect injury mechanisms. This could explain the prevalence of rotated head postures during a crash reported by patients suffering from WAD. The results can be used for validating the active behavior of human body models in braking simulations with nominal and rotated head postures, and to gain a deeper understanding of neck injury mechanisms.

Zusammenfassung

Architectural parameters of skeletal muscle such as pennation angle provide valuable information on muscle function, since they can be related to the muscle force generating capacity, fiber packing, and contraction velocity. In this paper, we introduce a 3D ultrasound-based workflow for determining 3D fascicle orientations of skeletal muscles. We used a custom-designed automated motor driven 3D ultrasound scanning system for obtaining 3D ultrasound images. From these, we applied a custom-developed multiscale-vessel enhancement filter-based fascicle detection algorithm and determined muscle volume and pennation angle. We conducted trials on a phantom and on the human tibialis anterior (TA) muscle of 10 healthy subjects in plantarflexion (157 ± 7\$\$^\backslashcirc\$\$), neutral position (109 ± 7\$\$^\backslashcirc\$\$, corresponding to neutral standing), and one resting position in between (145 ± 6\$\$^\backslashcirc\$\$). The results of the phantom trials showed a high accuracy with a mean absolute error of 0.92 ± 0.59\$\$^\backslashcirc\$\$. TA pennation angles were significantly different between all positions for the deep muscle compartment; for the superficial compartment, angles are significantly increased for neutral position compared to plantarflexion and resting position. Pennation angles were also significantly different between superficial and deep compartment. The results of constant muscle volumes across the 3 ankle joint angles indicate the suitability of the method for capturing 3D muscle geometry. Absolute pennation angles in our study were slightly lower than recent literature. Decreased pennation angles during plantarflexion are consistent with previous studies. The presented method demonstrates the possibility of determining 3D fascicle orientations of the TA muscle in vivo.

Zusammenfassung

In legged locomotion, muscles undergo damped oscillations in response to the leg contacting the ground (an impact). How muscle oscillates varies depending on the impact situation. We used a custom-made frame in which we clamped an isolated rat muscle (M. gastrocnemius medialis and lateralis: GAS) and dropped it from three different heights and onto two different ground materials. In fully activated GAS, the dominant eigenfrequencies were 163 Hz, 265 Hz, and 399 Hz, which were signficantly higher (p < 0.05) compared to the dominant eigenfrequencies in passive GAS: 139 Hz, 215 Hz, and 286 Hz. In general, neither changing the falling height nor ground material led to any significant eigenfrequency changes in active nor passive GAS, respectively. To trace the eigenfrequency values back to GAS stiffness values, we developed a 3DoF model. The model-predicted GAS muscle eigenfrequencies matched well with the experimental values and deviated by − 3.8\%, 9.0\%, and 4.3\% from the passive GAS eigenfrequencies and by − 1.8\%, 13.3\%, and − 1.5\% from the active GAS eigenfrequencies. Differences between the frequencies found for active and passive muscle impact situations are dominantly due to the attachment of myosin heads to actin.

Zusammenfassung

Section snippets The Rode model's explanation of the FLR's ascending limb allegedly involves pushing forces in thin filaments The main Rockenfeller et al. argument to dismiss the Rode model is the wrong assertion that the Rode model describes the FLR’s ascending limb based on pushing or compressive forces in thin filaments. The thin filaments would be too soft to transmit relevant pushing forces. However, in the Rode model, thin filaments are always pulled away from the Z-disk. Furthermore, Rockenfeller et al. wrongly assert that swXBs generate pushing forces on thin filaments in the Rode model and that the The Rockenfeller model ignores geometrical changes developing on the FLR’s ascending limb The Rockenfeller model assumes a hexagonal filament lattice as in optimal overlap down to 0.4-μm half-sarcomere length (with about 1 μm being the optimal length) and that the lattice distances progressively increase with shortening due to volume constancy. These assumptions ignore several geometrical changes in the half-sarcomere that occur during shortening and hamper the predictive power of the model in the range of the FLR’s ascending limb. For example, the Rockenfeller model predicts noThe Rockenfeller model assumes effective force in the region of double thin-filament overlap Double thin-filament overlap starts to develop when thin filaments slide through the M-line near optimal half-sarcomere length (left-hand side of the FLR plateau). The Rockenfeller model assumes that XBs are formed in the region of double thin-filament overlap. This assumption leads to effective force in this region and cannot explain Trombitás and Tigyi-Sebes’ experiments (8). Trombitás and Tigyi-Sebes stretched rigor muscle fibers leading to the detachment of thin filaments from the Z-disk. The Rockenfeller model's effective overlap function is mechanically inconsistent on the FLR's ascending limb One basis of the Rockenfeller model’s force calculation is the effective filament overlap, the theoretical capacity to produce isometric force depending on half-sarcomere length without effects of interfilament spacing. Surprisingly, the effective filament overlap (their Figure 1 in (3)) is straight at about 0.8-μm half-sarcomere length. First, when thick-filament tips slide through the Z-disk at this length, the myosin heads meet thin filaments of opposite polarity and form swXBs in their

Zusammenfassung

Section snippets The Rode model's explanation of the FLR's ascending limb allegedly involves pushing forces in thin filaments The main Rockenfeller et al. argument to dismiss the Rode model is the wrong assertion that the Rode model describes the FLR’s ascending limb based on pushing or compressive forces in thin filaments. The thin filaments would be too soft to transmit relevant pushing forces. However, in the Rode model, thin filaments are always pulled away from the Z-disk. Furthermore, Rockenfeller et al. wrongly assert that swXBs generate pushing forces on thin filaments in the Rode model and that the The Rockenfeller model ignores geometrical changes developing on the FLR’s ascending limb The Rockenfeller model assumes a hexagonal filament lattice as in optimal overlap down to 0.4-μm half-sarcomere length (with about 1 μm being the optimal length) and that the lattice distances progressively increase with shortening due to volume constancy. These assumptions ignore several geometrical changes in the half-sarcomere that occur during shortening and hamper the predictive power of the model in the range of the FLR’s ascending limb. For example, the Rockenfeller model predicts noThe Rockenfeller model assumes effective force in the region of double thin-filament overlap Double thin-filament overlap starts to develop when thin filaments slide through the M-line near optimal half-sarcomere length (left-hand side of the FLR plateau). The Rockenfeller model assumes that XBs are formed in the region of double thin-filament overlap. This assumption leads to effective force in this region and cannot explain Trombitás and Tigyi-Sebes’ experiments (8). Trombitás and Tigyi-Sebes stretched rigor muscle fibers leading to the detachment of thin filaments from the Z-disk. The Rockenfeller model's effective overlap function is mechanically inconsistent on the FLR's ascending limb One basis of the Rockenfeller model’s force calculation is the effective filament overlap, the theoretical capacity to produce isometric force depending on half-sarcomere length without effects of interfilament spacing. Surprisingly, the effective filament overlap (their Figure 1 in (3)) is straight at about 0.8-μm half-sarcomere length. First, when thick-filament tips slide through the Z-disk at this length, the myosin heads meet thin filaments of opposite polarity and form swXBs in their

Zusammenfassung

Abstract The stomach is a vital organ responsible for food storage, digestion, and transport. Stomach diseases are of great economic and medical importance and require a large number of bariatric surgeries every year. To improve medical interventions, in silico modeling of the gastrointestinal tract has gained popularity in recent years to study stomach functioning. Because of the great structural and nutritional similarity between the porcine and human stomach, the porcine stomach is a suitable surrogate for the development and validation of gastric models. This study presents a realistic 3D geometry model of the porcine stomach based on a photogrammetric reconstruction of a real organ. Layer thicknesses of the stomach wall's mucosa and tunica muscularis were determined by more than 1900 manual measurements at different locations. Layer thickness distributions show mean mucosal and muscle thicknesses of 2.29 ± 0.45 mm and 2.83 ± 0.99 mm, respectively. In general, layer thicknesses increase from fundus (mucosa: 1.82 ± 0.19 mm, muscle layer: 2.59 ± 0.32 mm) to antrum (mucosa: 2.69 ± 0.31 mm, muscle layer: 3.73 ± 1.05 mm). The analysis of stomach asymmetry with respect to an idealized symmetrical stomach model, an approach often used in the literature, revealed volumetric deviations of 45%, 15%, and 92% for the antrum, corpus, and fundus, respectively. The present work also suggests an algorithm for the computation of longitudinal and circumferential directions at local points. These directions are useful for the implementation of material anisotropy. In addition, we present data on the passive pressure-volume relationship of the organ and perform an exemplary finite-element simulation, where we demonstrate the applicability of the model. We encourage others to utilize the geometry model featuring profound asymmetry for future model-based investigations on stomach functioning.

Zusammenfassung

In vivo, the force–velocity relation (F–v–r) is typically derived from the torque–angular velocity relation (T–ω–r), which is subject to two factors that may influence resulting measurements: tendon compliance and preload prior to contraction. The in vivo plantar flexors’ T–ω–r was determined during preloaded maximum voluntary shortening contractions at 0–200°/s. Additionally, we used a two factor block simulation study design to independently analyze the effects of preload and tendon compliance on the resulting T–ω–r. Therefore, we replicated the in vivo experiment using a Hill-type muscle model of the gastrocnemius medialis. The simulation results matched a key pattern observed in our recorded in vivo experimental data: during preloaded contractions, torque output of the muscle was increased when compared with non-preloaded contractions from literature. This effect increased with increasing contraction velocity and can be explained by a rapidly recoiling tendon, allowing the contractile element to contract more slowly, thus developing higher forces compared with non-preloaded contractions. Our simulation results also indicate that a more compliant tendon results in increased ankle joint torques. The simulation and the experimental data clearly show that the deduction of the in vivo F–v–r from the T–ω–r is compromised due to the two factors preloading and tendon compliance.

Zusammenfassung

Musculoskeletal disorders (MSD) are a widespread problem, often regarding the lumbar region. Exoskeletons designed to support the lower back could be used in physically demanding professions with the intention of reducing the strain on the musculoskeletal system, e.g., by lowering task-related muscle activation. The present study aims to investigate the effect of an active exoskeleton on back muscle activity when lifting weights. Within the framework of the study, 14 subjects were asked to lift a 15 kg box with and without an active exoskeleton which allows the adjustment of different levels of support, while the activity of their M. erector spinae (MES) was measured using surface electromyography. Additionally, the subjects were asked about their overall rating of perceived exertion (RPE) during lifting under various conditions. Using the exoskeleton with the maximum level of support, the muscle activity was significantly lower than without exoskeleton. A significant correlation was found between the exoskeleton’s support level and the reduction of MES activity. The higher the support level, the lower the observed muscle activity. Furthermore, when lifting with the maximum level of support, RPE was found to be significantly lower than without exoskeleton too. A reduction in the MES activity indicates actual support for the movement task and might indicate lower compression forces in the lumbar region. It is concluded that the active exoskeleton supports people noticeably when lifting heavy weights. Exoskeletons seem to be a powerful tool for reducing load during physically demanding jobs and thus, their use might be helpful in lowering the risk of MSD.

Zusammenfassung

Neuromuscular control loops feature substantial communication delays, but mammals run robustly even in the most adverse conditions. In vivo experiments and computer simulation results suggest that muscles’ preflex—an immediate mechanical response to a perturbation—could be the critical contributor. Muscle preflexes act within a few milliseconds, an order of magnitude faster than neural reflexes. Their short-lasting action makes mechanical preflexes hard to quantify in vivo. Muscle models, on the other hand, require further improvement of their prediction accuracy during the non-standard conditions of perturbed locomotion. Our study aims to quantify the mechanical work done by muscles during the preflex phase (preflex work) and test their mechanical force modulation. We performed in vitro experiments with biological muscle fibers under physiological boundary conditions, which we determined in computer simulations of perturbed hopping. Our findings show that muscles initially resist impacts with a stereotypical stiffness response—identified as short-range stiffness—regardless of the exact perturbation condition. We then observe a velocity adaptation to the force related to the amount of perturbation similar to a damping response. The main contributor to the preflex work modulation is not the change in force due to a change in fiber stretch velocity (fiber damping characteristics) but the change in magnitude of the stretch due to the leg dynamics in the perturbed conditions. Our results confirm previous findings that muscle stiffness is activity-dependent and show that also damping characteristics are activity-dependent. These results indicate that neural control could tune the preflex properties of muscles in expectation of ground conditions leading to previously inexplicable neuromuscular adaptation speeds.

Zusammenfassung

Significant trends in the vehicle industry are autonomous driving, micromobility, electrification and the increased use of shared mobility solutions. These new vehicle automation and mobility classes lead to a larger number of occupant positions, interiors and load directions. As safety systems interact with and protect occupants, it is essential to place the human, with its variability and vulnerability, at the center of the design and operation of these systems. Digital human body models (HBMs) can help meet these requirements and are therefore increasingly being integrated into the development of new vehicle models. This contribution provides an overview of current HBMs and their applications in vehicle safety in different driving modes. The authors briefly introduce the underlying mathematical methods and present a selection of HBMs to the reader. An overview table with guideline values for simulation times, common applications and available variants of the models is provided. To provide insight into the broad application of HBMs, the authors present three case studies in the field of vehicle safety: (i)~in-crash finite element simulations and injuries of riders on a motorcycle; (ii)~scenario-based assessment of the active pre-crash behavior of occupants with the Madymo multibody HBM; (iii)~prediction of human behavior in a take-over scenario using the EMMA model.

Zusammenfassung

Vehicle accidents can cause neck injuries which are costly for individuals and society. Safety systems could be designed to reduce the risk of neck injury if it were possible to accurately simulate the tissue-level injuries that later lead to chronic pain. During a crash, reflexes cause the muscles of the neck to be actively lengthened. Although the muscles of the neck are often only mildly injured, the forces developed by the neck’s musculature affect the tissues that are more severely injured. In this work, we compare the forces developed by MAT_156, LS-DYNA’s Hill-type model, and the newly proposed VEXAT muscle model during active lengthening. The results show that Hill-type muscle models underestimate forces developed during active lengthening, while the VEXAT model can more faithfully reproduce experimental measurements.

Zusammenfassung

In vivo, the force–velocity relation (F–v–r) is typically derived from the torque–angular velocity relation (T–ω–r), which is subject to two factors that may influence resulting measurements: tendon compliance and preload prior to contraction. The in vivo plantar flexors’ T–ω–r was determined during preloaded maximum voluntary shortening contractions at 0–200°/s. Additionally, we used a two factor block simulation study design to independently analyze the effects of preload and tendon compliance on the resulting T–ω–r. Therefore, we replicated the in vivo experiment using a Hill-type muscle model of the gastrocnemius medialis. The simulation results matched a key pattern observed in our recorded in vivo experimental data: during preloaded contractions, torque output of the muscle was increased when compared with non-preloaded contractions from literature. This effect increased with increasing contraction velocity and can be explained by a rapidly recoiling tendon, allowing the contractile element to contract more slowly, thus developing higher forces compared with non-preloaded contractions. Our simulation results also indicate that a more compliant tendon results in increased ankle joint torques. The simulation and the experimental data clearly show that the deduction of the in vivo F–v–r from the T–ω–r is compromised due to the two factors preloading and tendon compliance.

Zusammenfassung

The human sensorimotor control system has exceptional abilities to perform skillful actions. We easily switch between strenuous tasks that involve brute force, such as lifting a heavy sewing machine, and delicate movements such as threading a needle in the same machine. Using a structure with different control architectures, the motor system is capable of updating its ability to perform through our daily interaction with the fluctuating environment. However, there are issues that make this a difficult computational problem for the brain to solve. The brain needs to control a nonlinear, nonstationary neuromuscular system, with redundant and occasionally undesired degrees of freedom, in an uncertain environment using a body in which information transmission is subject to delays and noise. To gain insight into the mechanisms of motor control, here we survey movement laws and invariances that shape our everyday motion. We then examine the major solutions to each of these problems in the three parts of the sensorimotor control system, sensing, planning, and acting. We focus on how the sensory system, the control architectures, and the structure and operation of the muscles serve as complementary mechanisms to overcome deviations and disturbances to motor behavior and give rise to skillful motor performance. We conclude with possible future research directions based on suggested links between the operation of the sensorimotor system across the movement stages.

Zusammenfassung

The force developed by actively lengthened muscle depends on different structures across different scales of lengthening. For small perturbations, the active response of muscle is well captured by a linear-time-invariant (LTI) system: a stiff spring in parallel with a light damper. The force response of muscle to longer stretches is better represented by a compliant spring that can fix its end when activated. Experimental work has shown that the stiffness and damping (impedance) of muscle in response to small perturbations is of fundamental importance to motor learning and mechanical stability, while the huge forces developed during long active stretches are critical for simulating and predicting injury. Outside of motor learning and injury, muscle is actively lengthened as a part of nearly all terrestrial locomotion. Despite the functional importance of impedance and active lengthening, no single muscle model has all of these mechanical properties. In this work, we present the viscoelastic-crossbridge active-titin (VEXAT) model that can replicate the response of muscle to length changes great and small. To evaluate the VEXAT model, we compare its response to biological muscle by simulating experiments that measure the impedance of muscle, and the forces developed during long active stretches. In addition, we have also compared the responses of the VEXAT model to a popular Hill-type muscle model. The VEXAT model more accurately captures the impedance of biological muscle and its responses to long active stretches than a Hill-type model and can still reproduce the force-velocity and force-length relations of muscle. While the comparison between the VEXAT model and biological muscle is favorable, there are some phenomena that can be improved: the low frequency phase response of the model, and a mechanism to support passive force enhancement.Competing Interest StatementThe authors have declared no competing interest.

Zusammenfassung

Eccentric muscle loading encompasses several unique features compared to other types of contractions. These features include increased force, work, and performance at decreased oxygen consumption, reduced metabolic cost, improved energy efficiency, as well as decreased muscle activity. This review summarises explanatory approaches to long-standing questions in terms of muscular contraction dynamics and molecular and cellular mechanisms underlying eccentric muscle loading. Moreover, this article intends to underscore the functional link between sarcomeric components, emphasising the fundamental role of titin in skeletal muscle. The giant filament titin reveals versatile functions ranging from sarcomere organisation and maintenance, providing passive tension and elasticity, and operates as a mechanosensory and signalling platform. Structurally, titin consists of a viscoelastic spring segment that allows activation-dependent coupling to actin. This titin-actin interaction can explain linear force increases in active lengthening experiments in biological systems. A three-filament model of skeletal muscle force production (mediated by titin) is supposed to overcome significant deviations between experimental observations and predictions by the classic sliding-filament and cross-bridge theories. Taken together, this review intends to contribute to a more detailed understanding of overall muscle behaviour and force generation—from a microscopic sarcomere level to a macroscopic multi-joint muscle level—impacting muscle modelling, the understanding of muscle function, and disease.

Zusammenfassung

Insight into the global deformation of the urinary bladder during passive and active phases is crucial for understanding the biomechanics and function of the organ. Therefore, in the present study, the three-dimensional deformations of the porcine urinary bladder were investigated using 10 cameras in ex vivo experiments. Voltages between 20 V and 40 V were applied to induce contraction without outflow (isovolumetric) and against different back pressures (isobaric). The fluid volume in the bladder and the fluid volume pushed out of the bladder in the active state were measured. During filling, a roughly constant pressure of 2.5–4 cmH2O was measured for a large volume range, followed by a steep increase. Overall, the urinary bladder shape changes from elliptical to spherical in the active phase, resulting in a more homogeneous stress field. The active pressure decreases with increasing volume, while the actively generated stress increases up to 65 kPa at the maximum volume examined. Smaller filling volumes and lower back pressures allowed complete emptying, whereas higher back pressures prevent full emptying from larger filling states. Finally, a recently developed three-dimensional model was used to describe the active and passive bladder characteristics in order to qualitatively represent the mechanical properties. Overall, this study provides for the first time a comprehensive experimental data set at organ level that leads to an improved understanding of load transfer mechanisms within the urinary bladder and serves to validate corresponding models.

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BACKGROUND: Reactive performance is an important component of rhythmic gymnastics. So far, it is unclear whether additional plyometric training in female gymnasts shows an increase in performance. OBJECTIVE: The aim of the study was to examine the effect of additional plyometric training in rhythmic gymnastics on the reactive jumping performance and strength of the lower leg muscles. METHODS: Fifteen rhythmic gymnasts (age: 12.3 ± 2.6 years, height: 1.47 ± 0.12 m, body weight: 37.3 ± 9.3 kg, BMI: 16.7 ± 2.1 kg*m-2; competition level: national and international championships, Tanner stages I–III) participated in the study. The athletes were assigned to an experimental (EG) and a control group (CG). The EG performed plyometric exercises three times per week in addition to the regular training. Before and after six weeks of training the reactive jump performance, the work of dorsi flexors and plantar flexors performed during isokinetic plantarflexion, as well as the performance in two sport-specific tests were measured. RESULTS: In contrast to the CG, in the EG the jump height (pre: 24.8; post: 27.25 cm; p< 0.05) and the reactive-strength-index (pre: 1.01; post: 1.19; p< 0.01) increased significantly. The EG achieved significant improvements in the counter movement jump test (pre: 27.0 cm; post: 31.5 cm; p< 0.01) and in the sport specific double rope jump test (jumps per minute, pre: 18.0; post: 23.0; p< 0.01). Furthermore, a significant increase in work performed during plantarflexion was found in the EG for the right leg (pre: 24.9 J; post: 29.7 J; p< 0.01) and a tendency to increase for the left leg (pre: 26.4 J; post: 37.7 J; p= 0.05). CONCLUSION: Both reactive strength and dynamic force can be efficiently increased by plyometric training. It may be recommended to include plyometric exercises in the training regime of rhythmic gymnasts.

Zusammenfassung

Ecccentric muscle contractions are fundamental to everyday life. They occur markedly in jumping, running, and accidents. Following an initial force rise, stretching of a fully activated muscle can result in a phase of decreasing force (“Give”) followed by force redevelopment. However, how the stretch velocity affects “Give” and force redevelopment remains largely unknown. We investigated the force produced by fully activated single-skinned fibers of rat extensor digitorum longus muscles during long stretches. Fibers were pulled from length 0.85 to 1.3 optimal fiber length at a rate of 1\%, 10\%, and 100\% of the estimated maximum shortening velocity. “Give” was absent in slow stretches. Medium and fast stretches yielded a clear “Give.” After the initial force peak, forces decreased by 11.2\% and 27.8\% relative to the initial peak force before rising again. During the last half of the stretch (from 1.07 to 1.3 optimal fiber length, which is within the range of the expected descending limb of the force-length relationship), the linear force slope tripled from slow to medium stretch and increased further by 60\% from medium to fast stretch. These results are compatible with forcible cross-bridge detachment and redevelopment of a cross-bridge distribution, and a viscoelastic titin contribution to fiber force. Accounting for these results can improve muscle models and predictions of multibody simulations.NEW & NOTEWORTHY Eccentric muscle contractions are part of our daily lives. We found that force increased monotonically during slow stretches of fully activated muscle fibers, whereas higher stretch velocities resulted in an increasing drop in force after an initial increase and a final steeper rise in force. Cross-bridges cannot explain the observed force traces. This requires a viscoelastic non-cross-bridge contribution. Considering these results can improve muscle models and predictions of multibody simulations.

Zusammenfassung

How myofilaments operate at short mammalian skeletal muscle lengths is unknown. A common assumption is that thick (myosin-containing) filaments get compressed at the Z-disc. We provide ultrastructural evidence of sarcomeres contracting down to 0.44 µm—approximately a quarter of thick filament resting length—in long-lasting contractions while apparently keeping a regular, parallel thick filament arrangement. Sarcomeres produced force at such extremely short lengths. Furthermore, sarcomeres adopted a bimodal length distribution with both modes below lengths where sarcomeres are expected to generate force in classic force–length measurements. Mammalian fibres did not restore resting length but remained short after deactivation, as previously reported for amphibian fibres, and showed increased forces during passive re-elongation. These findings are incompatible with viscoelastic thick filament compression but agree with predictions of a model incorporating thick filament sliding through the Z-disc. This more coherent picture of mechanical mammalian skeletal fibre functioning opens new perspectives on muscle physiology

Zusammenfassung

Legged locomotion has evolved as the most common form of terrestrial locomotion. When the leg makes contact with a solid surface, muscles absorb some of the shock-wave accelerations (impacts) that propagate through the body. We built a custom-made frame to which we fixated a rat (Rattus norvegicus, Wistar) muscle (m. gastrocnemius medialis and lateralis: GAS) for emulating an impact. We found that the fibre material of the muscle dissipates between 3.5 and 23 mycro ranging from fresh, fully active to passive muscle material, respectively. Accordingly, the corresponding dissipated energy in a half-sarcomere ranges between 10.4 and 68zJ, respectively. At maximum activity, a single cross-bridge would, thus, dissipate 0.6\% of the mechanical work available per ATP split per impact, and up to 16\% energy in common, submaximal, activities. We also found the cross-bridge stiffness as low as 2.2 pNnm, which can be explained by the Coulomb-actuating cross-bridge part dominating the sarcomere stiffness. Results of the study provide a deeper understanding of contractile dynamics during early ground contact in bouncy gait.

Zusammenfassung

Legged locomotion has evolved as the most common form of terrestrial locomotion. When the leg makes contact with a solid surface, muscles absorb some of the shock-wave accelerations (impacts) that propagate through the body. We built a custom-made frame to which we fixated a rat (Rattus norvegicus, Wistar) muscle (m. gastrocnemius medialis and lateralis: GAS) for emulating an impact. We found that the fibre material of the muscle dissipates between 3.5 and \$\$23\backslash,\backslashupmu \backslashhbox \J\\$\$ranging from fresh, fully active to passive muscle material, respectively. Accordingly, the corresponding dissipated energy in a half-sarcomere ranges between 10.4 and \$\$68\backslash,z\backslashhbox \J\\$\$, respectively. At maximum activity, a single cross-bridge would, thus, dissipate 0.6\% of the mechanical work available per ATP split per impact, and up to 16\% energy in common, submaximal, activities. We also found the cross-bridge stiffness as low as \$\$2.2\backslash,\backslashhbox \pN\\backslash,\backslashhbox \nm\^\-1\\$\$, which can be explained by the Coulomb-actuating cross-bridge part dominating the sarcomere stiffness. Results of the study provide a deeper understanding of contractile dynamics during early ground contact in bouncy gait.

Zusammenfassung

Muscle architecture, which includes parameters like fascicle length, pennation angle, and physiological cross-sectional area, strongly influences skeletal muscles' mechanical properties. During maturation, the muscle architecture has to adapt to a growing organism. This study aimed to develop an architectural model capable of predicting the complete 3D fascicle architecture for primarily unipennate muscles of an arbitrary age, based on fascicle data for an initial age. For model development, we collected novel data on 3D muscle architecture of the rabbit (Oryctolagus cuniculus) M. plantaris of eight animals ranging in age from 29 to 106 days. Experimental results show that plantaris muscle belly length increases by 73\%, whereas mean fascicle length and mean pennation angle increases by 39 and 14\%, respectively. Those changes were incorporated into the model. In addition to the data collected for M. plantaris the predictions of the model were compared to existing literature data of rabbit M. soleus and M. gastrocnemius medialis. With an error of −1.0þinspace±þinspace8.6\% for relative differences in aponeurosis length, aponeurosis width, muscle height, and muscle mass, the model delivered good results matching interindividual differences. For future studies, the model could be utilized to generate realistic architectural data sets for simulation studies.

Zusammenfassung

During growth there are serious changes in the skeletal muscles to compensate for the changed requirements in terms of body weight and size. In this study, the age-dependent (between 21 and 100 days) mechanical and microstructural properties of rabbit soleus muscle tissue were investigated. For this purpose, morphological properties (animal mass, soleus muscle mass, tibial length) were measured at 5 different times during aging. On the other hand, fibre orientation-dependent axial and semi-confined compression experiments were realised. In addition, the essential components (muscle fibres, extracellular matrix, remaining components), dominating the microstructure of muscle tissue, were analysed. While the mechanical results show hardly any age-dependent differences, the morphological and microstructural results show clear age-dependent differences. All morphological parameters increase significantly (animal mass by 839.2%, muscle mass 1050.6%, tibial length 233.6%). In contrast, microstructural parameters change differently. The percentage of fibres (divided into slow-twitch (ST) and fast-twitch (FT) fibres) increases significantly (137.6%), while the proportions of the extracellular matrix and the remaining components (48.2% and 46.1%) decrease. At the same time, the cross-sectional area of the fibres increases significantly (697.9%). The totality of this age-dependent information provides a deeper understanding of age-related changes in muscle structure and function and may contribute to successful development and validation of growth models in the future. Statement of significance This article reports the first comprehensive data set on age-dependent morphological (animal mass, soleus muscle mass, tibial length), mechanical (axial and semi-confined compression), and microstructural (muscle fibres, extracellular matrix, remaining components) properties of the rabbit soleus muscle. On the one hand, the results of this study contribute to the understanding of muscle mechanics and thus to understanding of load transfer mechanisms inside the muscle tissue during growth. On the other hand, these results are relevant to the fields of constitutive formulation of age-dependent muscle tissue.

Zusammenfassung

Muscle architecture, which includes parameters like fascicle length, pennation angle, and physiological cross-sectional area, strongly influences skeletal muscles' mechanical properties. During maturation, the muscle architecture has to adapt to a growing organism. This study aimed to develop an architectural model capable of predicting the complete 3D fascicle architecture for primarily unipennate muscles of an arbitrary age, based on fascicle data for an initial age. For model development, we collected novel data on 3D muscle architecture of the rabbit (Oryctolagus cuniculus) M. plantaris of eight animals ranging in age from 29 to 106 days. Experimental results show that plantaris muscle belly length increases by 73%, whereas mean fascicle length and mean pennation angle increases by 39 and 14%, respectively. Those changes were incorporated into the model. In addition to the data collected for M. plantaris the predictions of the model were compared to existing literature data of rabbit M. soleus and M. gastrocnemius medialis. With an error of −1.0 ± 8.6% for relative differences in aponeurosis length, aponeurosis width, muscle height, and muscle mass, the model delivered good results matching interindividual differences. For future studies, the model could be utilized to generate realistic architectural data sets for simulation studies.

Zusammenfassung

Uniaxial tensile experiments are a standard method to determine the contractile properties of smooth muscles. Smooth muscle strips from organs of the urogenital and gastrointestinal tract contain multiple muscle layers with different muscle fiber orientations, which are frequently not separated for the experiments. During strip activation, these muscle fibers contract in deviant orientations from the force-measuring axis, affecting the biomechanical characteristics of the tissue strips. This study aimed to investigate the influence of muscle layer separation on the determination of smooth muscle properties. Smooth muscle strips, consisting of longitudinal and circumferential muscle layers (whole-muscle strips WMS), and smooth muscle strips, consisting of only the circumferential muscle layer (separated layer strips SLS), have been prepared from the fundus of the porcine stomach. Strips were mounted with muscle fibers of the circumferential layer inline with the force-measuring axis of the uniaxial testing setup. The force–length (FLR) and force–velocity relationships (FVR) were determined through a series of isometric and isotonic contractions, respectively. Muscle layer separation revealed no changes in the FLR. However, the SLS exhibited a higher maximal shortening velocity and a lower curvature factor than WMS. During WMS activation, the transversally oriented muscle fibers of the longitudinal layer shortened, resulting in a narrowing of this layer. Expecting volume constancy of muscle tissue, this narrowing leads to a lengthening of the longitudinal layer, which counteracted the shortening of the circumferential layer during isotonic contractions. Consequently, the shortening velocities of the WMS were decreased significantly. This effect was stronger at high shortening velocities.

Zusammenfassung

Muscle force, work, and power output during concentric contractions (active muscle shortening) are increased immediately following an eccentric contraction (active muscle lengthening). This increase in performance is known as the stretch-shortening cycle (SSC)-effect. Recent findings demonstrate that the SSC-effect is present in the sarcomere itself. More recently, it has been suggested that cross-bridge (XB) kinetics and non-cross-bridge (non-XB) structures (e.g., titin and nebulin) contribute to the SSC-effect. As XBs and non-XB structures are characterized by a velocity dependence, we investigated the impact of stretch-shortening velocity on the SSC-effect. Accordingly, we performed in vitro isovelocity ramp experiments with varying ramp velocities (30, 60, and 85% of maximum contraction velocity for both stretch and shortening) and constant stretch-shortening magnitudes (17% of the optimum sarcomere length) using single skinned fibers of rat soleus muscles. The different contributions of XB and non-XB structures to force production were identified using the XB-inhibitor Blebbistatin. We show that (i) the SSC-effect is velocity-dependent—since the power output increases with increasing SSC-velocity. (ii) The energy recovery (ratio of elastic energy storage and release in the SSC) is higher in the Blebbistatin condition compared with the control condition. The stored and released energy in the Blebbistatin condition can be explained by the viscoelastic properties of the non-XB structure titin. Consequently, our experimental findings suggest that the energy stored in titin during the eccentric phase contributes to the SSC-effect in a velocity-dependent manner.

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Objectives: To evaluate patients' satisfaction and evolution of pre-operative symptoms at 6 months following laparoscopic cornuectomy for hysteroscopic sterilization implants removal. Material and methods: Retrospective study including all patients undergoing laparoscopic cornuectomy for implants removal in a tertiary care setting from January 2017 to October 2018. All women suffered from persistent and treatment-resistant gynecologic and non-gynecologic complaints since sterilization procedure. Patents' satisfaction was evaluated with the PGI-I questionnaire at 2 and 6 months following surgery. Results: Overall, 104 patients were enrolled. Main symptoms comprised asthenia (n = 80), chronic pelvic pain (n = 80), arthralgia (n = 70), abnormal uterine bleeding (n = 42) and headache (n = 40). Cornuectomy was feasible in all cases and led to complete devices removal in 101 women. Mean length of stay was 1.8 days, while outpatient management was feasible in 45.2 % of cases. One grade 3 complication occurred along the study period (hemoperitoneum requiring reoperation). Surgery was associated with a significant decrease in symptom occurrence, except for alopecia and weight loss. Patients' satisfaction was high: 91 % at 2 months and 97.6 % at 6 months reported an improvement in their health status compared to baseline situation. Satisfaction regarding each symptom was consistent with overall assessment, with most patients reporting significant improvement at both 2 and 6 months. Conclusion: Laparoscopic cornuectomy is feasible and associated with high mid-term satisfaction in patients suffering from adverse effects attributed to hysteroscopic sterilization implants.

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Gas chromatography-olfactometry-mass spectrometry (GC-O-MS) has been very useful in identifying aroma compounds from within the complex matrix of wine. Supplementary separation can be required to overcome co-elution of volatiles or other sensory-directed chromatographic strategies are needed, including multidimensional chromatography and preparative fraction collection coupled to GC. Studies investigating 'overripe orange' aroma in sweet Sauternes wine and the similar 'apricot' aroma in Viognier wine were conducted. Wines with the targeted aroma attributes were selected and concentrated wine extracts prepared. GC-O found no individual aroma compounds with the targeted aroma attribute. Semi-preparative HPLC was used to obtain less complex fractions of the wine extracts. The fractions were eluted in water/ethanol and, therefore, could be smelled directly. Fractions with the targeted aroma character were further resolved by GC-preparative fraction collection (GC-PFC). Recombinational GC-PFC demonstrated the importance of the components within a 4 min preparative GC fraction to the 'overripe orange' aroma of typical Bordeaux dessert wine. In Viognier wine, monoterpenes linalool, α-terpineol and geraniol as well as benzaldehyde were found to be associated with the 'apricot' character. Thus, several wine aroma compounds interact for these specific aromas to be perceived. This sensory-led combination of separation techniques is a powerful tool for the identification of key compounds responsible for specific aromas across the wine and beverage industries.

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Muscle models are used in basic research to understand the physical mechanisms of muscle contraction, and in applied research for investigating movements. The structure and biomechanical function of half-sarcomeres, tendon, and aponeurosis govern the whole muscle's force production. This chapter emphasizes fundamental biophysical mechanisms within half-sarcomeres, as in general the quality of muscle model predictions, be they one- or three-dimensional, depends on the description of these force generators. Additionally, important elements of 3D muscle architecture will be presented and the impact of geometrical changes on muscle force generation during contraction will be explained. Existing 3D muscle modelling approaches and their validation will be discussed.

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Moment arm-angle functions (MA-a-functions) are commonly used to estimate in vivo muscle forces in humans. However, different MA-a-functions might not only influence the magnitude of the estimated muscle forces but also change the shape of the muscle's estimated force-angle relationship (F-a-r). Therefore, we investigated the influence of different literature based Achilles tendon MA-a-functions on the triceps surae muscle--tendon unit F-a-r. The individual in vivo triceps torque--angle relationship was determined in 14 participants performing maximum voluntary fixed-end plantarflexion contractions from 18.3°þinspace±þinspace3.2° plantarflexion to 24.2°þinspace±þinspace5.1° dorsiflexion on a dynamometer. The resulting F-a-r were calculated using 15 literature-based in vivo Achilles tendon MA-a-functions. MA-a-functions affected the F-a-r shape and magnitude of estimated peak active triceps muscle--tendon unit force. Depending on the MA-a-function used, the triceps was solely operating on the ascending limb (nþinspace=þinspace2), on the ascending limb and plateau region (nþinspace=þinspace12), or on the ascending limb, plateau region and descending limb of the F-a-r (nþinspace=þinspace1). According to our findings, the estimated triceps muscle--tendon unit forces and the shape of the F-a-r are highly dependent on the MA-a-function used. As these functions are affected by many variables, we recommend using individual Achilles tendon MA-a-functions, ideally accounting for contraction intensity-related changes in moment arm magnitude.

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Aims Vaginal surface electromyography (sEMG) is a tool used for the diagnosis and therapeutic intervention of urinary incontinence. Current sEMG systems differ in regard to electrode arrangement and data reproducibility. The aim of this study was to determine the intrasession, intraday, and interday reliabilities of sEMG parameters using a probe with circumferential electrode-position. Methods The intrasession, intraday, and interday reliabilities of maximum isometric voluntary contractions (MVC) of the pelvic floor muscles were assessed for 19 healthy continent women. Three sEMG parameters that are used to describe muscle activity were verified: maximal EMG (EMGmax), mean over 500 ms around EMGmax (EMGA0.5), and mean over 2 seconds during MVC plateau (EMGA2-4). Relative and absolute reliability parameters were calculated, and the statistical methods described by Bland and Altman were applied to the data. Results We observed substantial reliabilities for all obtained parameters (EMGmax, EMGA2-4, and EMGA0.5) in regard to the intrasession measurements (ICC = 0.93-0.97; CI = 0.86-0.99). Overall, the intraday reliability has been moderate (ICC = 0.64-0.75; CI = 0.27-0.90). EMGmax (ICC = 0.75; CI = 0.45-0.90) and EMGA2-4 (ICC = 0.73, CI = 0.42-0.89) were higher than EMGA0.5 (ICC = 0.64; CI = 0.27-0.85). However, the interday reliability was only fair for EMGmax (ICC = 0.48; CI = 0.04-0.77) and EMGA0.5 (ICC = 0.51; CI = 0.07-0.78) but moderate for EMGA2-4 (ICC = 0.65; CI = 0.28-0.85). Conclusions This intrasession, intraday, and interday reliability results are similar to the results reported in the literature using probes with longitudinally oriented bars. The mean sEMG signal over 2 seconds (EMGA2-4) exhibited the highest reliability and is recommended for further studies. The interday reliability might be enhanced by considering the menstruation cycle.

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The consideration of the temporal and electromyographic (EMG) characteristics of stretch-shortening cycles (SSC) are crucial for the conceptualization of discipline-specific testing and training. Since leg muscles are first stretched (eccentric) and then contracted (concentric) during rowing, it can be assumed that the entire muscle tendon complex performs a SSC. Thus, it should be elucidated whether the rowing cycle can be attributed to either a slow or fast SSC. Therefore, EMG of the vastus medialis and gastrocnemius were captured (nþinspace=þinspace10, 22.8þinspace±þinspace3.1 years, 190þinspace±þinspace6þinspacecm, 82.1þinspace±þinspace9.8þinspacekg) during (single scull) rowing and subsequently compared to typical slow (countermovement jump, CMJ) and fast (drop jump, DJ) SSCs. The elapsed time between the EMG onset and the start of the eccentric phase was monitored. The pre-activation phase (PRE, before the start of the eccentric phase) and the reflex-induced activation phase (RIA 30--120þinspacems after the start of the eccentric phase) have been classified. Notable muscular activity was observed during DJ before the start of the eccentric phase (PRE) as well as during RIA. In contrast, neither CMJ nor rowing revealed any EMG-activity in these two phases. Interestingly, CMJ and race-specific rowing showed an EMG-onset during the eccentric phase. We conclude that rowing is more attributable to a slow SSC and implies that fast SSC does not reflect discipline specific muscle action and could hamper rowing-performance-enhancement.

Zusammenfassung

The resulting muscular performance is considered notably higher during a stretch shortening cycle (SSC) compared to an isolated concentric contraction. Thus, the present study examined the occurrence and magnitude of rowing performance enhancement after a flexion–extension cycle (FEC) of the legs compared to both concentric contractions only and isometric pre-contraction. Therefore, 31 sub-elite male rowers (age: 25 ± 6 years, height: 1.90 ± 0.02 m, weight: 91 ± 10 kg, weekly training volume: 11.4 ± 5.3 h/week, rowing experience: 7.1 ± 2.7 years) randomly completed (a) isolated concentric rowing strokes (DRIVE), (b) single FEC-type rowing strokes (SLIDE-DRIVE), and (c) rowing strokes with an isometric pre-contraction (ISO-DRIVE). The resulting rowing power (Prow), leg power (Pleg), and work per stroke (WPS) were recorded using motion-capturing, force, and rotation sensors. Comparison of DRIVE and SLIDE-DRIVE revealed significantly (p < 0.05) higher Prow (+11.8 ± 14.0%), Pleg (+19.6 ± 26.7%), and WPS (+9.9 ± 10.5%) during SLIDE-DRIVE. Compared to ISO-DRIVE, Pleg (+9.8 ± 26.6%) and WPS (+6.1 ± 6.7%) are again significantly (p < 0.05) higher for SLIDE-DRIVE. In conclusion, notably higher work and power outputs (compared to an isolated concentric contraction) during FEC rowing referred to an underlying SSC. Future ultrasound studies should elucidate whether a real SSC on the muscle tendon unit level account for these performance enhancements.

Zusammenfassung

Abstract Each stretch-shortening-cycle (SSC) in elite sports (e.g. jumping, cycling), is characterised by utilising optimal movement-parameters (e.g. muscle shortening velocity), for maximum power (jump height, cycle velocity). It is however unclear if relevant SSC movement-parameters in rowing, such as stroke rate and gearing, have to be maximised to obtain maximum power output or if an optimum relation emerges. Thus, we measured rowing-power (Prow), leg-power (Pleg) and work-per-stroke (WPS) at of varying stroke rates (20–45 spm), gearings (lever-changes 0.87–0.90 m) and drag factors (100–180 Ws3/m3) during rowing. Experienced sub-elite young athletes performed sprint-series on (single scull, n = 69, 20 ± 2 years, 186 ± 7 cm, 84 ± 9 kg) and off the water (rowing-ergometer, n = 30, 19 ± 3 years, 185 ± 11 cm, 77 ± 19 kg). Prow increased with stroke rate for ergometer-test (r = 0.97, p < 0.001) and boat measurement (r = 0.98, p < 0.001) by 2.7\%/stroke and 4.4\%/stroke, respectively. Interestingly, stroke rate had a high impact on WPS (r = 0.79, p < 0.001) during boat measurement, compared to no (or specifically no high) impact on WPS (r = −0.10, p = 0.166) during ergometer-measurements. Drag factor (ergometer: r = 0.83, p < 0.001) and gearing (boat: r = 0.60, p < 0.001) yielded moderate to high correlations to Prow. These results indicate that no optimum stroke rate, gearing and drag factor exist for maximum power in rowing (sprint-measurement-range). Accordingly, the measurements yielded maximum power for maximum stroke rate, gearing, and drag factor.

Zusammenfassung

The punctum fixum-punctum mobile model has been introduced in previous publications. It describes general principles of intersegmental neuromuscular succession patterns to most efficiently generate specific movement intentions. The general hypothesis of this study is that these principles—if they really do indicate a fundamental basis for efficient movement generation—should also be found in intramuscular coordination and should be indicated by “longitudinal sequencing” between fibers according to the principles of the punctum fixum-punctum mobile model. Based on this general hypothesis an operationalized model was developed for the rectus femoris muscle (RF), to exemplarily scrutinize this hypothesis for the RF. Electromyography was performed for 14 healthy male participants by using two intramuscular fine wire electrodes in the RF (placed proximal and distal), three surface electrodes over the RF (placed proximal, middle, and distal), and two surface electrodes over the antagonists (m. biceps femoris and m. semitendinosus). Three movement tasks were measured: kicking movements; deceleration after sprints; and passively induced backward accelerations of the leg. The results suggest that proximal fibers can be activated independently from distal fibers within the RF. Further, it was shown that the hypothesized function of “intramuscular longitudinal sequencing” does exist during dynamic movements. According to the punctum fixum-punctum mobile model, the activation succession between fibers changes direction (from proximal to distal or inversely) depending on the intentional context. Thus, the results seem to support the general hypothesis for the RF and could be principally in line with the operationalized “inter-fiber to tendon interaction model”.

Zusammenfassung

The stomach serves as food reservoir, mixing organ and absorption area for certain substances, while continually varying its position and size. Large dimensional changes during ingestion and gastric emptying of the stomach are associated with large changes in smooth muscle length. These length changes might induce history-effects, namely force depression (FD) following active muscle shortening and force enhancement (FE) following active muscle stretch. Both effects have impact on the force generating capacity of the stomach, and thus functional relevance. However, less is known about history-effects and active smooth muscle properties of stomach smooth muscle. Thus, the aim of this study was to investigate biomechanical muscle properties as force-length and force-velocity relations (FVR) of porcine stomach smooth muscle strips, extended by the analysis of history-effects on smooth muscle force. Therefore, in total n = 54 tissue strips were dissected in longitudinal direction from the ventral fundus of porcine stomachs. Different isometric, isotonic, and isokinetic contraction protocols were performed during electrical muscle stimulation. Cross-sectional areas (CSA) of smooth muscles were determined from cryo-histological sections stained with Picrosirius Red. Results revealed that maximum smooth muscle tension was 10.4 ± 2.6 N/cm2. Maximum shortening velocity (Vmax ) and curvature factor (curv) of the FVR were 0.04 ± 0.01 optimum muscle length/s and 0.36 ± 0.15, respectively. The findings of the present study demonstrated significant (P < 0.05) FD up to 32% maximum muscle force (Fim ) and FE (up to 16% Fim ) of gastric muscle tissue, respectively. The FE- and FD-values increased with increasing ramp amplitude. This outstanding muscle behavior is not accounted for in existing models so far and strongly supports the idea of a holistic reflection of distinct stomach structure and function. For the first time this study provides a comprehensive set of stomach smooth muscle parameters including classic biomechanical muscle properties and history-dependent effects, offering the possibility for the development and validation of computational stomach models. Furthermore, this data set facilitates novel insights in gastric motility and contraction behavior based on the re-evaluation of existing contractile mechanisms. That will likely help to understand physiological functions or dysfunctions in terms of gastric accommodation and emptying.

Zusammenfassung

Purpose The aim of the study was to examine pH heterogeneity during fatigue induced by neuromuscular electrical stimulation (NMES) using phosphorus magnetic resonance spectroscopy (31P-MRS). It is hypothesized that three pH components would occur in the 31P-MRS during fatigue, representing three fiber types. Methods The medial gastrocnemius of eight subjects was stimulated within a 3-Tesla whole body MRI scanner. The maximal force during stimulation (Fstim) was examined by a pressure sensor. Phosphocreatine (PCr), adenosintriphosphate, inorganic phosphate (Pi), and the corresponding pH were estimated by a nonvolume-selective 31P-MRS using a small loop coil at rest and during fatigue. Results During fatigue, Fstim and PCr decreased to 27% and 33% of their initial levels, respectively. In all cases, the Pi peak increased when NMES was started and split into three different peaks. Based on the single Pi peaks during fatigue, an alkaline (6.76 ± 0.08), a medium (6.40 ± 0.06), and an acidic (6.09 ± 0.05) pH component were observed compared to the pH (7.02 ± 0.02) at rest. Conclusion It is suggested that NMES is able to induce pH heterogeneity in the medial gastrocnemius, and that the single Pi peaks represent the different muscle fiber types of the skeletal muscle. Magn Reson Med 77:2097–2106, 2017. © 2016 International Society for Magnetic Resonance in Medicine

Zusammenfassung

There are several studies dealing with experimental and structural analyses of skeletal muscles that are aimed at gaining a better understanding of three-dimensional muscle deformation and force generation. A variety of these contributions have performed structural or mechanical analyses, but very few have combined these approaches at different levels. To fill this gap, the present study aims to bring together three-dimensional micro-structural and mechanical findings in rabbit M. plantaris to study load transfer mechanisms inside the muscle during passive loading and active muscle contraction. During these two deformation states, the three-dimensional surface of the aponeurosis–tendon complex was recorded using optical measurement systems. In this way, the strain distribution on the muscle can be calculated to interpret the load transfer mechanisms inside the muscle. The results show that the three-dimensional strain distribution during muscle activation is completely different from the distribution during passive loading. Under both loading conditions, the strain distribution is irregular. To interpret these findings, the gross try and the fascicle architecture of the M. plantaris were determined. In doing so, a highly complex microstructure featuring tube- and sail-like structure was identified. Moreover, a compartmentalisation of the muscle into two compartments was detected. The smaller, bipennated muscle compartment was embedded into the larger, unipennated compartment. To the authors׳ knowledge, this type of inner structure has never been previously documented in single-headed muscles.

Zusammenfassung

The present study examined whether different pre-information conditions could lead to a volitional modulation of the occurrence and magnitude of the bilateral force deficit (BFD) during isometric leg press. Twenty trained male adults (age: 24.5 ± 1.7 years; weight: 77.5 ± 7.1 kg; height: 1.81 ± 0.05 m) were examined on three days within a week. Isometric leg press was performed on a negatively inclined leg press slide. Each participant completed three maximal isometric strength test sessions with different pre-information conditions given in a graphical chart: no pre-information (NPI; first day), false pre-information (FPI; bilateral force > sum of unilateral forces; second or third day) and correct pre-information (CPI; bilateral force < sum of unilateral forces; second or third day) during bilateral, unilateral-left and unilateral-right leg-press. The sum of left- and right-sided force values were calculated for bilateral (FBL = FBL_left + FBL_right) and unilateral (FUL = FUL_left + FUL_right) analyses. Force data for NPI revealed: Mean (SD): FUL_NPI = 3023 N (435) vs. FBL_NPI = 2812 (453); FPI showed FUL_FPI = 3013 N (459) vs. FBL_FPI = 2843 (446) and the CPI revealed FUL_CPI = 3035 (425) vs. FBL_CPI = 2844 (385). The three (no, false, correct) x 2 (FUL, FBL) rANOVA revealed a high significant main effect of Force (F = 61.82, p < 0.001). No significant main effect of the factor Condition and no significant interaction between Force x Condition was observed. The BFD does not rely on the trueness of the given pre-information (no, false, correct). Cognition-based volitional influences on the BFD on supra-spinal level seem negligible. Key pointsBFD is reliable occurring phenomenonAvailable theoretical knowledge does not affect the BFDAlternating sport should include alternating strength exercises.