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

PURPOSE: 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).

METHODS

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.

RESULTS

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.

CONCLUSION

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.