ECSS Paris 2023: OP-BM02
INTRODUCTION: Unaccustomed eccentric exercise induces acute muscle injury and soreness [1], involving alterations of the myofibrillar ultrastructure [2], muscle fiber membrane [3], and disruption of the extracellular matrix. Such alterations impair force transmission and lead to strength loss, commonly used as an indirect biomarker of muscle damage (EIMD). The along-fiber shear modulus, assessed by ultrasound shear wave elastography (SWE), has been shown to increase in the presence of muscle injury [4]. However, the direction-dependent mechanical and microstructural in-vivo changes in skeletal muscle following EIMD are poorly understood. This study aimed to characterize the time course of these adaptations using angle-resolved SWE and the Nakagami m parameter. METHODS: To investigate the evolution of along- and cross-muscle fibers SM (SML - SMX) and m parameters (mL – mT) in the biceps brachii at three elbow joint angles (0° [full extension], 45°, and 90°) following an eccentric exercise protocol. Twenty young adults (9M, 11W) completed four sessions: baseline, 48h, 7d, and 14d post-exercise. The exercise protocol consisted of 3-6 sets of 10 eccentric elbow flexions performed at 120°·s⁻¹ using an isokinetic dynamometer (System 3; Biodex Medical Systems). Ultrasound scans (Mach 30, SuperSonic Imagine) were acquired at the muscle mid-belly in longitudinal and transverse orientations. Angle-resolved SWE was used to assess SM [5]. SM and m values were analyzed within standardized regions of interest. RESULTS: Strength significantly decreased at 48 h (−18.2%; p < 0.001) and fully recovered by 14d (p < 0.001), confirming EIMD and subsequent recovery. SML showed a significant session×angle interaction (p < 0.01), increasing at 48h only at 0° (+58.8%; p < 0.001), while remaining unchanged at other angles. SMT was unaffected (p = 0.41), highlighting the directional specificity of the mechanical alterations under passive loading. In contrast, mT and mL were not influenced by joint angle (p > 0.10) but exhibited a delayed temporal response: no change was observed at 48h (p = 0.81), whereas a peak increase occurred at 7d in all angles (+16.1% to +17.8%; p < 0.001). CONCLUSION: Our findings show that mechanical (SM) and microstructural (m) adaptations following eccentric-induced muscle damage evolve with distinct temporal patterns, with mechanical changes dependent on muscle length and microstructural alterations consistent across angles, likely reflecting different physiological processes involved in post EIMD remodeling. Notably, the directional-dependent of mechanical responses contrasted with the isotropic behavior of m parameters. These results highlight the importance of assessing muscle tissue anisotropy for understanding structural disorganization and remodeling after EIMD. Thanks to angle-resolved SWE, tensile and shear anisotropy can now be measured, and these data will be analyzed in future work. [1] Clarkson, 2002 [2] Fridén, 1981 [3] Armstrong, 1990 [4] Lacourpaille 2014 [5] Andrade, 2025
Read CV Baptiste BizetECSS Paris 2023: OP-BM02
INTRODUCTION: During eccentric contractions (ECC), reducing fascicle strain is important for minimizing muscle damage and the risk of muscle strain injuries [1]. It is well known that the compliance of the external tendon contributes to reducing muscle fascicle strain by absorbing elastic energy during ECC [2]. Given that aponeurosis, an intramuscular sheet-like tendon, also has similar properties [3], its compliance may also reduce fascicle strain. However, how aponeurosis plays a role in fascicle mechanics during ECC remains unclear. We aimed to investigate how the mechanical properties of the aponeurosis are associated with fascicle mechanics during ECC. METHODS: For twenty-one healthy adults, the shear elastic modulus of superficial and deep aponeuroses along their length of the medial gastrocnemius (MG) was measured at rest using shear wave elastography, as a stiffness index. Then, they performed a maximal isometric preactivation, followed by a maximal ECC while the ankle moved from 20° plantarflexion to 20° dorsiflexion at 30°/s. During contraction, fascicle length and fascicle angle (FA) of the MG were measured with B-mode ultrasonography. The ratio of muscle belly segment strain to fascicle strain was calculated as muscle gear [4]. Relationships between the shear elastic modulus of aponeuroses and fascicle mechanics were examined using Spearman’s rank correlation. RESULTS: Contrary to the hypothesis, the shear elastic modulus of aponeuroses was not significantly correlated with fascicle strain during ECC (superficial: ρ=0.206, p=0.369; deep: ρ=0.010, p=0.964). Meanwhile, within observed range of 13.1–32.2 kPa, individuals with a lower shear elastic modulus of the deep aponeurosis tended to show greater change in FA from rest to the initial state of ECC (i.e., at the end of preactivation) (ρ=–0.604, p=0.004), and greater FA at the initial state of ECC was correlated with higher gear during ECC (ρ=0.960, p<0.001). Consequently, individuals with a lower shear elastic modulus of the deep aponeurosis tended to exhibit higher gear during subsequent ECC (ρ=–0.701, p<0.001). CONCLUSION: Although aponeurosis stiffness was not directly related to fascicle strain, its compliance was linked to a greater FA at the initial state of ECC. As a greater FA enhanced gear [4], the compliant aponeurosis was associated with the higher gear (i.e., smaller fascicle strain per muscle belly segment strain) during subsequent ECC. These findings indicate that aponeurosis can play a role in reducing relative fascicle strain through modification of the initial state of ECC and subsequent gearing mechanism during ECC, providing novel insights into the functional relevance of the aponeurosis in skeletal muscle. Maintaining compliant aponeurosis might be one of the strategies for reducing the risk of muscle strain injuries, which warrants further investigation. [1] Guilhem et al., Acta Physiol. 2016 [2] Azizi and Roberts, Proc Biol Sci. 2015 [3] Arellano et al., Proc Biol Sci. 2019 [4] Pinto et al., Biol Open. 2023
Read CV Hiroko YoshidaECSS Paris 2023: OP-BM02
INTRODUCTION: During level walking, humans adopt gait patterns that minimize the net energy cost (NCw). Metabolic energy is required by muscles to generate force and perform total positive mechanical work (Wtot). The main component of Wtot is the external work (Wext), which is the work performed to lift and accelerate the body’s center of mass. The pendular exchange of potential and kinetic energy (Rstep) reduces Wext, thereby minimizing NCw (1). Altered Rstep has been associated with a higher NCw in older and obese adults compared with young and lean individuals (2,3). However, older adults logically exhibited lower Rstep (4), whereas adults with obesity showed higher NCw despite a greater Rstep (2), making the relationship between Rstep and NCw equivocal. This study thus aimed to examine the acute effects of modulating the pendular mechanism via visual biofeedback on the energetics and mechanics of walking in healthy individuals. METHODS: 15 adults walked 5 min at 4 km/h on an instrumented treadmill in 3 different experimental conditions: 1) normal walking to assess the preferred Rstep values (0%), 2) at -10% and 3) +10% of preferred Rstep values using a real-time visual biofeedback (VB). Gas exchanges were collected to assess the NCw. The ground reaction forces were measured to generate real-time VB and to assess Wext and Rstep during the trials. Locomotor efficiency was calculated as Wext divided by the NCw. RESULTS: NCw increased significantly at +10% (p=0.01) and -10% (p<0.001) Rstep conditions compared with the preferred value (0%). Wext significantly increased at -10% than at 0% (p=0.01) and +10% (p<0.001) Rstep conditions, whereas it did not significantly differ between 0% and +10% (p=0.52) Rstep conditions. Locomotor efficiency significantly decreased at +10% Rstep (p=0.01) compared with 0% Rstep conditions but did not significantly differ between 0% and -10% Rstep conditions (p=1). CONCLUSION: These results confirm, at the individual level, that whole-body energy minimization is a key determinant of human gait behavior. The increased NCw in the +10% Rstep condition, despite a more effective pendular mechanism and Wext values similar to the preferred Rstep condition, indicates that walking optimization reflects a trade-off between pendulum-like energy savings and muscular efficiency. References: 1. Peyré-Tartaruga, L. A., Dewolf, A. H., di Prampero, P. E., Fábrica, G., Malatesta, D., Minetti, A. E., Monte, A., Pavei, G., Silva-Pereyra, V., Willems, P. A., & Zamparo, P. (2021). Experimental Physiology, 106(9), 1897‑1908. 2. Fernández Menéndez, A., Uva, B., Favre, L., Hans, D., Borrani, F., & Malatesta, D. (2020). Journal of Applied Physiology (Bethesda, Md.: 1985), 129(1), 194‑203. 3. Malatesta, D., Simar, D., Dauvilliers, Y., Candau, R., Borrani, F., Prefaut, C., & Caillaud, C. (2003). Journal of Applied Physiology (Bethesda, Md.: 1985), 95(6), 2248‑2256. 4. Nùñez-Lisboa, M. N., & Dewolf, A. H. (2025). npj aging, 11(1).
Read CV Valentin LucECSS Paris 2023: OP-BM02