Vigorous physical activity enhances intermuscular coordination between ankle muscles during gait.

Intermuscular coordination (IMC) refers to the nervous system's ability to synchronise muscle activity. While regular physical activity is thought to enhance IMC, the nature of this relationship remains poorly understood. Here we investigate whether high and low IMC between ankle muscles during gait differs based on physical activity levels and individuals' weekly engagement in vigorous activities among young adults. Twenty-five participants (10 females) aged 20-34 years were evaluated. Surface electromyography (EMG) recorded activity of the tibialis anterior (TA), soleus (SOL), and medial gastrocnemius (GM) at 1000 Hz during 10 walking trials at 1 m/s (90 m total). Each EMG epoch included 200 ms before to 600 ms after heel contact and was analysed using causal empirical mode decomposition to identify intrinsic mode functions (IMFs) with stronger causal relationships among muscle pairs. Coordination between selected IMFs of the SOL-TA and SOL-MG muscle pairs was assessed using cross-approximate entropy (XApEn). K-means clustering of XApEn values identified low and high IMC groups (p < 0.001). Proportion of physically active individuals was 83 % in high IMC group, compared to 23 % in low IMC group (p = 0.003). Weekly vigorous activity was greater in the active group (240 vs. 0 min, p = 0.010) and showed a significant moderate correlation with IMC between antagonistic muscles. Physical activity enhances intermuscular coordination among ankle muscles during gait. This emphasizes the role of physical activity, particularly vigorous activity, in enhancing neuromuscular function and counteracting the negative effects of sedentary behaviour on the neuromuscular system.