The influence of exercise-induced fatigue on neuromuscular control strategies during lifting tasks: A muscle synergy study based on wavelet packet transform

Repetitive lifting-related low back pain is a significant health issue among workers, in which fatigue is generally identified as a critical risk factor. However, there is currently a lack of research on the effects of exercised induced fatigue on neuromuscular control patterns, which can be identified through muscle synergy based on the signals of surface electromyographic (sEMG). This study employs a wavelet packet transform (WPT) combined with non-negative matrix factorization (NNMF) to investigate the lifting task from the perspective of muscle synergy and to explore the characteristics of muscle synergy patterns under exercise-induced fatigue. Eleven participants were recruited to perform a repetitive lifting task until subjective fatigue. Utilizing the NNMF method, three modules associated with the lifting task were identified. Notably, the module primarily involving the TA and LES exhibited a higher activation level, indicating that this module requires greater neural resource regulation. However, the effect of fatigue on muscle synergy was not found in NNMF method. Additionally, the WPT-NNMF method revealed that the effects of fatigue on different frequency bands and synergy modules were inconsistent. Overall, as the frequency band increased, the impact of exercise-induced fatigue on muscle synergy intensified, with a more pronounced effect observed in the module characterized by TA and LES compared to the other two modules.