Slow Intermuscular Oscillations are Associated with Cocontraction Steadiness

Purpose: Voluntary muscle contraction often involves low-frequency correlated neural oscillations across muscles, which may degrade steady cocontraction between antagonistic muscles with distinct levels of activation per each muscle (unbalanced cocontraction). The purposes of the studywere 1) to determinewhether there is an association between the low-frequency correlated EMG oscillations and the performance of steady unbalanced cocontraction across individuals and 2) to determine whether a bout of out-of-phase cocontraction practice reduces the in-phase low-frequency correlated neural oscillations and improves the performance of steady unbalanced cocontraction. Methods: Healthy young adults were divided into three intervention groups: cocontraction, contraction, and control. All participants were tested for unbalanced steady cocontractions with antagonistic muscles about the elbow joint before and after a bout of intervention with the visual feedback of surface EMG. During the intervention period, the cocontraction group practiced an out-of-phase cocontraction, whereas the contraction group practiced agonist contractions. Results: Mean squared error and variance of EMG amplitude were positively correlated with low-frequency EMG coherence G3 Hz across subjects, which became more prevalent after the intervention period. There was no specific effect of the cocontraction intervention on these variables. Conclusion: These findings suggest that individuals with less low-frequency correlated neural oscillations tend to perform steady cocontraction more skillfully, and the lowfrequency correlated oscillations may not be acutely modulated by one bout of out-of-phase cocontraction practice.