No abstract

The interaction between gastrocnemius medialis (GM) muscle and Achilles tendon, i.e., muscle-tendon unit (MTU) interaction, plays an important role in minimizing the metabolic cost of running. Foot-strike pattern (FSP) has been suggested to alter MTU interaction and subsequently the metabolic cost of running. However, metabolic data from experimental studies on FSP are inconsistent, and a comparison of MTU interaction between FSP is still lacking. We, therefore, investigated the effect of habitual rearfoot and mid-/forefoot striking on MTU interaction, ankle joint work, and plantar flexor muscle force production while running at 10 and 14 km/h. GM muscle fascicles of 9 rearfoot and 10 mid-/forefoot strikers were tracked using dynamic ultrasonography during treadmill running. We collected kinetic and kinematic data and used musculoskeletal models to determine joint angles and calculate MTU lengths. In addition, we used dynamic optimization to assess plantar flexor muscle forces. During ground contact, GM fascicle shortening ( P = 0.02) and average contraction velocity ( P = 0.01) were 40–45% greater in rearfoot strikers than mid-/forefoot strikers. Differences in contraction velocity were especially prominent during early ground contact. Moreover, GM ( P = 0.02) muscle force was greater during early ground contact in mid-/forefoot strikers than rearfoot strikers. Interestingly, we did not find differences in stretch or recoil of the series elastic element between FSP. Our results suggest that, for the GM, the reduced muscle energy cost associated with lower fascicle contraction velocity in mid-/forefoot strikers may be counteracted by greater muscle forces during early ground contact. NEW & NOTEWORTHY Kinetic and kinematic differences between foot-strike patterns during running imply (not previously reported) altered muscle-tendon interaction. Here, we studied muscle-tendon interaction using ultrasonography. We found greater fascicle contraction velocities and lower muscle forces in rearfoot compared with mid-/forefoot strikers. Our results suggest that the higher metabolic energy demand due to greater fascicle contraction velocities might offset the lower metabolic energy demand due to lower muscle forces in rearfoot compared with mid-/forefoot strikers.

Achilles tendon stiffness determines calf muscle functioning during functional activities. However, contrasting evidence was found in studies comparing Achilles tendon stiffness in older and younger adults. Therefore, this systematic review compares Achilles tendon stiffness and elastic modulus in older and younger adults and reviews functional implications. Studies revealed by systematic bibliographic searches were included if healthy older adults were investigated, and if Achilles tendon stiffness was measured using ultrasound and dynamometry. Meta-analyses were performed to compare Achilles tendon stiffness and elastic modulus in older and younger adults. Achilles tendon stiffness (weighted standardized mean difference = 1.40, 95% confidence intervals [0.42-2.38]) and elastic modulus (weighted standardized mean difference = 1.74, 95% confidence intervals [0.99-2.49]) were decreased in older compared with younger adults. Decreased Achilles tendon stiffness was related to walking performance and balance. Possibly, decreased Achilles tendon stiffness is caused by altered elastic modulus in older adults. Training interventions increasing Achilles tendon stiffness could improve functional capacity.

Observational research suggests that in children with cerebral palsy, the altered arm swing is linked to instability during walking. Therefore, the current study investigates whether children with cerebral palsy use their arms more than typically developing children, to enhance gait stability. Evidence also suggests an influence of walking speed on gait stability. Moreover, previous research highlighted a link between walking speed and arm swing. Hence, the experiment aimed to explore differences between typically developing children and children with cerebral palsy taking into account the combined influence of restricting arm swing and increasing walking speed on gait stability. Spatiotemporal gait characteristics, trunk movement parameters and margins of stability were obtained using three dimensional gait analysis to assess gait stability of 26 children with cerebral palsy and 24 typically developing children. Four walking conditions were evaluated: (i) free arm swing and preferred walking speed; (ii) restricted arm swing and preferred walking speed; (iii) free arm swing and high walking speed; and (iv) restricted arm swing and high walking speed. Double support time and trunk acceleration variability increased more when arm swing was restricted in children with bilateral cerebral palsy compared to typically developing children and children with unilateral cerebral palsy. Trunk sway velocity increased more when walking speed was increased in children with unilateral cerebral palsy compared to children with bilateral cerebral palsy and typically developing children and in children with bilateral cerebral palsy compared to typically developing children. Trunk sway velocity increased more when both arm swing was restricted and walking speed was increased in children with bilateral cerebral palsy compared to typically developing children. It is proposed that facilitating arm swing during gait rehabilitation can improve gait stability and decrease trunk movements in children with cerebral palsy. The current results thereby partly support the suggestion that facilitating arm swing in specific situations possibly enhances safety and reduces the risk of falling in children with cerebral palsy.

We present and evaluate a new approach to estimate calf muscle-tendon parameters and calculate calf muscle-tendon function during walking. We used motion analysis, ultrasound, and EMG data of the calf muscles collected in six young and six older adults during treadmill walking as inputs to a new optimal estimation algorithm. We used estimated parameters or scaled generic parameters in an existing approach to calculate muscle fiber lengths and activations. We calculated the fit with experimental data in terms of root mean squared differences (RMSD) and coefficients of determination (R²). We also calculated the calf muscle metabolic energy cost. RMSD between measured and calculated fiber lengths and activations decreased and R² increased when estimating parameters compared to using scaled generic parameters. Moreover, R² between measured and calculated gastrocnemius medialis fiber length and soleus activations increased by 19 % and 70 %, and calf muscle metabolic energy decreased by 25% when using estimated parameters compared to using scaled generic parameters at speeds not used for estimation. This new approach estimates calf muscletendon parameters in good accordance with values reported in literature. The approach improves calculations of calf muscle-tendon interaction during walking and highlights the importance of individualizing calf muscle-tendon parameters.