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bioRxiv · 10.64898/2026.07.11.737916

Anticipatory modulation of motor unit discharge rate before rapid isometric elbow flexion force production

Park, J.·Park, J.-W.·Lee, S.·Choi, Y.-S.·Park, D.·Hur, H.·Kim, H.-S.
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Abstract

Surface electromyography (EMG) studies have demonstrated anticipatory muscle activation prior to predictable voluntary actions. However, the mechanism through which this preparation is expressed, whether through motor-unit recruitment or discharge-rate modulation, remains to be elucidated. We employed surface decomposition EMG to quantify motor-unit behavior prior to self-paced rapid isometric elbow-flexion force pulses. Twelve healthy young men were instructed to generate elbow-flexion pulse force at 30%, 40%, and 50% of the maximal voluntary contraction (MVC) at a self-selected time. Motor-unit activity was decomposed from the biceps brachii and triceps brachii muscles, and the normalized active motor-unit number and mean discharge rate were analyzed prior to pulse onset. In the agonist, the pre-pulse increase mean discharge rate exhibited a higher value than the change in detected motor-unit count, particularly at the 40% and 50% MVC targets. The discharge-rate increase scaled with the target force, with a heightened response observed in high-threshold as compared to low-threshold motor units. Antagonist recordings with sufficient decomposition yield exhibited a similar discharge-rate-dominant pattern; however, these data were available from a smaller sample size. Present findings suggest that discharge-rate modulation is a primary motor-unit-level feature of anticipatory preparation for rapid isometric force production.

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Park, J., Park, J.-W., Lee, S., Choi, Y.-S., Park, D., Hur, H., Kim, H.-S.. 2026-07-17. Anticipatory modulation of motor unit discharge rate before rapid isometric elbow flexion force production. https://doi.org/10.64898/2026.07.11.737916

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