Key result
Coactivating ~10% of motor units eliminates the transitory force decrease following stimulation frequency reduction.
Why the study?
The biomechanical background of the transitory force decrease following a sudden reduction in stimulation frequency in fast resistant motor units was studied to better understand force transmission mechanisms.
Population
Fast resistant motor units of rat medial gastrocnemius
Comparison
Stimulation with three-phase trains of stimuli under various biomechanical conditions
Design
Experimental study on isolated motor units
Authors
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Hypothesis-generating for motor unit force dynamics; leaves open translation to human rehabilitation pending clinical validation.
The transitory force decrease in fast resistant motor units following a reduction in stimulation rate is highly sensitive to biomechanical conditioning, suggesting dependence on force transmission disturbances by surrounding collagen.
Rakoczy et al. (2020) studied Motor unit transitory force decrease (n=10). Biomechanical conditioning (muscle stretch, coactivation, stimulation frequency changes) vs. Control conditions (e.g., different stretch levels, no coactivation) was evaluated on Amplitude of transitory force decrease. The transitory force decrease following a reduction in stimulation frequency is highest at optimal muscle stretch (100 mN) and eliminated by coactivation of ≥10% of motor units.
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