Cortical and Cortico-Muscular Network Modulation Pattern of Eccentric and Concentric Movements in Fatigue State

Lower extremity motor function deficits, combined with fatigue, are common in patients with neurological injuries. The interaction between motor deficits and fatigue further limits rehabilitation endurance and recovery. However, how different types of movement are modulated by the cortico-muscular network in response to a fatigue remains unclear. In this study, ten healthy subjects were recruited to perform sit-to-stand tasks (T1: concentric sit-to-stand, T2: eccentric stand-to-sit) in both pre-fatigue and post-fatigue states. During these tasks, electroencephalogram (EEG) and electromyogram (EMG) signals from the lower extremities were recorded. Muscle and mental fatigue were confirmed by EMG mean power frequency (MPF) and changes in EEG Lempel-Ziv complexity (LZC). Inter-cortical and cortico-muscular networks were analyzed using generalized partial directed coherence (GPDC), with clustering coefficient (CC) and global efficiency (GE) as network metrics. In the pre-fatigue state, T1 exhibited greater inter-cortical network connectivity compared to T2. In the post-fatigue state, T1 increased inter-cortical connectivity while T2 showed significant increases in CC and GE in the beta band (P = 0.018, P = 0.034). At the cortico-muscular level, T1 shifted the descending pathway from Beta band to Gamma band while T2 significantly upregulated the strength of descending cortico-muscular pathway and ascending pathways in both Beta and Gamma bands. These findings indicate concentric movements exhibited more compensation in inter-cortical connectivity and band shift in cortico-muscular network, while eccentric movements showed greater efficiency in inter-cortical level and stronger cortico-muscular network strength. This study reveals distinct modulation patterns for concentric and eccentric movements under fatigued conditions, which may provide insights for developing targeted training and therapeutic programs for rehabilitation.