Fatigue-induced alterations in arm swing contribution to countermovement jump mechanics

This study examined protocol-specific neuromuscular responses to acute fatigue during countermovement jump (CMJ) performance by comparing jumps performed with arm swing (CMJAS) and without arm swing (CMJNAS). Eighteen physically active male participants (age: 21.4 ± 1.4 years; height: 188.2 ± 5.7 cm; body mass: 80.5 ± 5.4 kg) performed CMJ with and without arm swing on separate days before and after acute fatigue induced by a 30-s Wingate test. Ground reaction forces were collected via force platform, and biomechanical variables were analyzed using Bayesian paired-samples t-tests and repeated-measures ANOVA. Bayesian analyses revealed extreme evidence for pre–post changes in vertical take-off velocity in both CMJAS (BF₁₀=369.74) and CMJNAS (BF₁₀=40.45), accompanied by extreme time×condition interaction evidence (BFincl=6142.38), indicating protocol-dependent modulation of take-off mechanics. Jump height derived from flight time showed extreme evidence in CMJAS (BF₁₀=219.89) and very strong evidence in CMJNAS (BF₁₀=17.48). CMJNAS demonstrated stronger evidence for fatigue-related alterations in relative maximal power (BF₁₀=20.05), peak concentric force (BF₁₀=2.49), and late push-off acceleration (BF₁₀=12.86), whereas corresponding changes in CMJAS were moderate or anecdotal. In contrast, average force, average power, early push-off acceleration, and eccentric braking variables showed little to no evidence for change across conditions. CMJ without arm swing is more sensitive to fatigue-induced alterations in lower-limb neuromuscular function, particularly in force–power output and late-phase propulsion. In contrast, CMJ with arm swing preserves global performance through whole-body coordination. These findings underscore the importance of protocol selection when CMJ is used for neuromuscular monitoring and fatigue assessment.