earticle

영어

This study examined the effects of fatigue and knee joint ankle on motor unit (MU) behavior, force steadiness, and intermuscular coherence between the soleus (SOL) and gastrocnemius medialis (GM) during isometric plantarflexion. Fourteen healthy males performed isometric plantarflexion at 30, 50, and 70% of maximal voluntary isometric contraction (MVIC) under two knee joint conditions: straight leg (0°, STR) and bent leg (90°, BENT) positions. Fatigue was induced via sustained contractions. High-density surface electromyography (EMG) from SOL and GM was decomposed to quantify MU parameters, including MU action potential amplitude (MUAP), firing rate (FR), recruitment threshold (ReTHR), and derecruitment threshold (DeTHR). Intermuscular coherence between MU spike trains from SOL and GM was analyzed across frequency bands. In post-fatigue, maximal force decreased significantly in both STR and BENT conditions (p < 0.01). Force steadiness significantly deteriorated post-fatigue in the BENT condition at 50% (p < 0.01) and 70% (p < 0.05) MVIC. In SOL, MUAP and FR increased post-fatigue across all conditions, while GM showed more selective increases at higher intensities. SOL exhibited higher MUAP in the BENT condition, whereas GM was greater activity in the STR condition. Recruitment thresholds in SOL and DeTHR in both muscles showed significant changes related to posture and fatigue. Notably, beta-band intermuscular coherence showed significant interaction effects at 50% and 70% (p < 0.05) MVIC, with the BENT condition showing increased coherence post-fatigue (p < 0.05). Fatigue induces muscle-specific and posture-dependent neuromuscular adaptations, including by enhanced MU synchronization and intermuscular coherence, particularly in bent knee positions.