Brent J Raiteri1, Daniel Hahn1,2. 1. Human Movement Science, Faculty of Sport Science, Ruhr University Bochum, Bochum, Germany. 2. School of Human Movement and Nutrition Sciences, The University of Queensland, Brisbane, Queensland, Australia.
Abstract
AIM: We investigated if residual force depression (rFD) is present during voluntary fixed-end contractions of human tibialis anterior (TA) and whether reducing TA's activation level after active shortening could reduce rFD. METHODS: Ten participants performed fixed-end dorsiflexion contractions to a low, moderate or high level while electromyography (EMG), dorsiflexion force and TA ultrasound images were recorded. Contractions were force- or EMG-matched and after the low or high contraction level was attained, participants respectively increased or decreased their force/EMG to a moderate level. Participants also performed moderate level contractions while the TA muscle-tendon unit (MTU) was lengthened during the force/EMG rise to the reference MTU length. RESULTS: Equivalent fascicle shortening over moderate and low to moderate level contractions did not alter EMG (P = 0.45) or dorsiflexion force (P = 0.47) at the moderate level. Greater initial fascicle shortening magnitudes (1.7 mm; P ≤ 0.01) to the high contraction level did not alter EMG (P = 0.45) or dorsiflexion force (P = 0.30) at the subsequent moderate level compared with moderate level contractions. TA MTU lengthening during the initial force/EMG rise reduced TA fascicle shortening (-2.5 mm; P ≤ 0.01), which reduced EMG (-3.9% MVC; P < 0.01) and increased dorsiflexion force (3.7% MVC; P < 0.01) at the moderate level compared with fixed-end moderate level contractions. CONCLUSION: rFD is present during fixed-end dorsiflexion contractions because fascicles actively shorten as force/EMG increases and rFD can be reduced by reducing the effective MTU compliance. A reduction in muscle activation level also reduces rFD by potentially triggering residual force enhancement-related mechanisms as force drops and some fascicles actively lengthen.
AIM: We investigated if residual force depression (rFD) is present during voluntary fixed-end contractions of human tibialis anterior (TA) and whether reducing TA's activation level after active shortening could reduce rFD. METHODS: Ten participants performed fixed-end dorsiflexion contractions to a low, moderate or high level while electromyography (EMG), dorsiflexion force and TA ultrasound images were recorded. Contractions were force- or EMG-matched and after the low or high contraction level was attained, participants respectively increased or decreased their force/EMG to a moderate level. Participants also performed moderate level contractions while the TA muscle-tendon unit (MTU) was lengthened during the force/EMG rise to the reference MTU length. RESULTS: Equivalent fascicle shortening over moderate and low to moderate level contractions did not alter EMG (P = 0.45) or dorsiflexion force (P = 0.47) at the moderate level. Greater initial fascicle shortening magnitudes (1.7 mm; P ≤ 0.01) to the high contraction level did not alter EMG (P = 0.45) or dorsiflexion force (P = 0.30) at the subsequent moderate level compared with moderate level contractions. TA MTU lengthening during the initial force/EMG rise reduced TA fascicle shortening (-2.5 mm; P ≤ 0.01), which reduced EMG (-3.9% MVC; P < 0.01) and increased dorsiflexion force (3.7% MVC; P < 0.01) at the moderate level compared with fixed-end moderate level contractions. CONCLUSION: rFD is present during fixed-end dorsiflexion contractions because fascicles actively shorten as force/EMG increases and rFD can be reduced by reducing the effective MTU compliance. A reduction in muscle activation level also reduces rFD by potentially triggering residual force enhancement-related mechanisms as force drops and some fascicles actively lengthen.
Authors: Martin Eric Héroux; Ida Anderman; Sofia Nykvist Vouis; Joanna Diong; Peter William Stubbs; Robert D Herbert Journal: J Appl Physiol (1985) Date: 2020-09-03
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