Task specific effects of fatigue on lower limb muscle synergies during single and double leg drop jumps in female athletes.

Background: Drop jump (DJ) tasks are widely used to assess lower-limb neuromuscular function and injury risk. Fatigue is a key factor elevating injury risk, yet its effects on neuromuscular control during single-leg drop jumps (SLDJ) and double-leg drop jumps (DLDJ), and whether these effects differ by task type, remain poorly understood. Methods: Fifteen female athletes performed SLDJ and DLDJ before and after a standardized fatigue protocol. Surface electromyography signals from nine lower-limb muscles were collected. Muscle synergies were extracted via non-negative matrix factorization, and synergy similarity was assessed using scalar product and Pearson correlation coefficients. Linear mixed-effects models examined differences in muscle contributions and temporal activation features. Results: Three muscle synergy modules were consistently identified across both tasks and fatigue conditions, with high inter-module similarity (scalar product and Pearson r > 0.80). Synergy structure remained stable regardless of task or fatigue, while task type and fatigue selectively modulated specific muscle contributions. Notably, vastus lateralis contribution showed opposing fatigue-related trends between tasks, and lateral gastrocnemius contribution decreased significantly after fatigue in SLDJ only. Conclusions: The central nervous system maintains a stable modular control strategy across DJ tasks and fatigue conditions. Adaptations to fatigue manifest primarily through task-specific modulation of intra-module muscle weights rather than restructuring of synergy organization. SLDJ demonstrated greater neuromuscular sensitivity to fatigue than DLDJ, indicating that single-leg landing tasks may be more susceptible to fatigue-induced alterations in neuromuscular control. These findings inform neuromuscular screening and targeted training strategies for female athletes.