Assessing the Contribution of Arm Swing to Countermovement Jump Height Using Three Different Measurement Methods in Physically Active Men

Background/Objectives: This study evaluated the reliability and validity of three methods to measure jump height during countermovement jumps performed with (CMJAS) and without (CMJNAS) arm swing: (1) an impulse–momentum method with force platforms (FPimp), (2) a flight time method with force platforms (FPtime), and (3) an inertial measurement unit (PUSH Band 2.0; PUSH2). Methods: Eighteen physically active men performed CMJAS and CMJNAS on force platforms while wearing PUSH2 over two days. Besides jump height, we computed intraclass correlation coefficients (ICC) and the absolute and relative increases in jump height due to arm swing, compared to CMJNAS. Results: The reliability of intra-session, inter-session, and concurrent measures were good to excellent (intra-session ICC2,1 = 0.957–0.979, inter-session ICC2,1 = 0.806–0.990, concurrent ICC3,1 = 0.940–0.973) for CMJAS and CMJNAS heights, in all three methods. The three methods showed high to very high reliability for both the absolute and relative indices of arm swing contribution (ICC2,1 = 0.649–0.812). FPtime significantly overestimated CMJNAS height relative to FPimp (p < 0.01). The absolute index of arm swing contribution was similar in FPimp and FPtime (p = 0.38) but higher in PUSH2 (p < 0.01), indicating that arm swing amplified overestimation. Conclusions: All three methods demonstrated high reliability for jump height measurements, but FPtime and PUSH2 misestimated jump height depending on jump modalities. Caution is advised when assessing the absolute and relative contribution of arm swing, because errors in CMJNAS and CMJAS height measurements can affect these values and their interpretation.