Effects of squat load and velocity on neuromuscular control strategies.

PURPOSE: This study investigated the effects of velocity and load on lower limb neuromuscular synergy during the concentric phase of the squat to inform resistance training design. METHODS: Surface electromyography (sEMG) signals from lower limb muscles were collected during squats performed under two loads (40% 1RM, 60% 1RM) and two velocities (fast, slow). Non-negative matrix factorization extracted muscle synergies, and functional networks were constructed based on sEMG frequency band coherence. RESULTS: Two synergies were identified during slow squats, compared to four during fast squats. Increased load resulted in higher activation weight and delayed peak activation of agonist muscles, while antagonist activation decreased during fast squats. Beta-band connectivity was stronger during slow squats, whereas Gamma-band connectivity dominated during fast squats. Global efficiency in the Gamma band peaked under both fast-light and slow-heavy conditions, revealing a significant interaction. For the Beta-band clustering coefficient, only the main effect of velocity was significant. CONCLUSIONS: Velocity determines synergy architecture (integrated for stability vs. decoupled for power), while load modulates gain and timing within this framework. For stability, slow training with 60% load is recommended; for explosive power, fast training with 40% load is optimal for maximizing acceleration.