BACKGROUND: The countermovement jump (CMJ) is a common assessment used to measure jumping capabilities and overall athletic performance. Previous studies have suggested differences in CMJ performance when performed with arms akimbo, commonly used in lab settings, versus using an arm swing, commonly used in field settings. It is possible that an arm swing may not only change overall performance, but the efficiency of the CMJ. Theoretically to have the most efficient jump, peak force should coincide with force at the low position. However, it is unknown if using an arm swing during the CMJ influences the efficiency of the CMJ. Therefore, the purpose of this study was to compare the effects of arm swing (AS) and no arm swing (NAS) on force profiles and jump efficiency during the CMJ. METHODS: Twenty-three recreationally trained males and females (age=23±3 yrs, height=171±15 cm, body mass=71±15 kg) participated. Participants completed six total CMJs, three with AS and three with NAS, in random order. Ground reaction forces were collected during all CMJ. Force at the low position of the countermovement, peak propulsive force, and countermovement depth were taken from the CMJ. CMJ efficiency was calculated as: (peak propulsive force - force at the low position)/peak propulsive force. Dependent samples t-tests examined differences for force at the low position, peak propulsive force, countermovement depth, and CMJ efficiency between AS and NAS. RESULTS: There were no significant differences between AS and NAS countermovement depth and peak propulsive force (p≥0.464). NAS had greater force at the low position and better CMJ efficiency than AS (p≤0.002). CONCLUSIONS: The present study demonstrates the potential variability associated with an arm swing when performing the CMJ. The differences in force at the low position and jump efficiency suggest that performing the CMJ with arms akimbo may yield a more efficient CMJ. This might suggest that the AS condition has less efficient jump profiles due to the poor arm swing mechanics and potential variability in arm movement. When using the AS technique, practitioners should prioritize improving arm mechanics to allow more efficient jumps. Future studies should consider further assessing the kinetics and kinematics of CMJs with and without an arm swing to better understand how upper-body movement influences CMJ efficiency.

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