Muscle Synergies During Countermovement Jump: Comparing Athletes and Nonathletes

This study investigated the neural timing control characteristics of countermovement jumps between elite athletes and nonathletes using muscle synergy theory. Twenty male participants (high-level group [HLG, N = 10] and untrained group [UG, N = 10]) performed the countermovement jump while surface electromyography from eight lower limb muscles and three-dimensional force plate data were recorded. Nonnegative matrix factorization extracted three muscle synergy modules, and bootstrap resampling with bias-corrected 95% confidence intervals (CIs) analyzed temporal parameters. Results demonstrated: (a) HLG achieved significantly greater jump height (95% CI: [-0.139, -0.026]); (b) HLG exhibited delayed activation onset (95% CI: [-0.227, -0.015]), peak timing (95% CI: [-0.300, -0.028]), and offset (95% CI: [-0.216, -0.014]) in Synergy module 1, delayed onset (95% CI: [-0.225, -0.054]) and offset (95% CI: [-0.224, -0.072]) in Synergy module 2, and delayed offset in Synergy module 3 (95% CI: [-0.197, -0.017]); and (c) HLG showed narrower full width at half maximum in Synergy module 1 (95% CI: [0.009, 0.094]), with no group differences in amplitude parameters. These findings suggest that, compared with UG, HLG exhibit delayed synergy activation timing during the countermovement jump. This temporal pattern may be associated with more effective use of the eccentric phase and more coordinated interjoint timing during propulsion.