Effects of drop height on muscle synergy patterns and estimated soft tissue power during drop jumps

This study examined height-related differences in lower-limb muscle synergies and estimated soft tissue power during drop jumps (DJs). Seventeen resistance-trained men performed DJs from seven heights (30–90 cm). Kinetic, kinematic, and surface electromyographic data were collected synchronously. Non-negative matrix factorization was used to extract muscle weighting matrices and temporal activation coefficients, while estimated soft tissue power was calculated as the residual between total mechanical power and modeled joint power. Linear mixed-effects models, one-dimensional statistical parametric mapping, and repeated-measures analysis of variance were used for statistical analysis. Three muscle synergy modules were identified: Synergy 1 was mainly weighted by the gastrocnemius muscles, Synergy 2 by the rectus femoris and vastus medialis, and Synergy 3 by the tibialis anterior. Muscle weighting structure did not differ significantly across heights. Synergy 1 showed a significant main effect of height on temporal activation during 30%–52% of the contact phase, whereas Synergy 3 showed significant differences during 10%–59% and 64%–100% ( P < 0.05). Estimated soft tissue power differed significantly across heights during several discrete intervals ( P < 0.05), and its contribution ratio showed a significant main effect of height ( P < 0.001, partial η 2 = 0.099). Overall, drop height was associated with localized changes in coordinated muscle activation and estimated non-joint mechanical energy exchanges, while synergy structure remained stable. These findings characterize acute height-related responses but do not identify an optimal drop height.