Influence of contraction intensity on high-density electromyography spatial parameters and motor unit recruitment of the triceps surae during plantarflexion

Abstract

The triceps surae is critical for movement but remains understudied. This study used high-density surface EMG (HDsEMG) to examine spatial features of the triceps surae during isometric plantarflexion. Seventy-four healthy adults (mean age = 22.8 ± 2.0 years) performed isometric contractions with 32-channel electrode grids on the medial and lateral gastrocnemius and soleus. Root mean square (RMS), median frequency (MDF), and coefficient of variation (CoV) were compared across muscles. The gastrocnemii exhibited significantly greater RMS than the soleus at all contraction intensities. The medial gastrocnemius showed significantly greater MDF at higher intensities, suggesting a greater contribution of fast-twitch muscle fibers. The lateral soleus had significantly higher CoV compared to the medial soleus and lateral gastrocnemius suggesting that the lateral placement captured muscle activity from surrounding musculature. Finally, motor unit decomposition was explored, and an open-source dataset was created. These findings highlight important differences in triceps surae recruitment, with clinical and research implications.