(41) PEAK YANK’S CONTRIBUTION TO JUMP HEIGHT DIFFERS BETWEEN COUNTERMOVEMENT JUMPS WITH AND WITHOUT ARM SWING

The countermovement jump (CMJ) is used to assess lower body power through force-time analysis. Recently, yank, the 1^st derivative of force (N×s^-1) representing instantaneous rate of force development (RFD), has been suggested to influence jump height (JH). Previous work suggests that eccentric RFD is a strong predictor of JH. While the arm swing has been demonstrated to influence CMJ performance, how the arm swing influences yank characteristics is less explored. PURPOSE: The purpose of this study was to assess the relationship between peak yank (PY) and CMJ performance with and without arm swing in recreationally trained jumpers.

Methods: Recreationally active males (n=5) and females (n=3) (X±SD, age=19.8±0.5 yrs., hheight=166.2±16.7 cm, mass=74.1±13.7 kg) completed three maximal CMJs with arm swing and three without arm swing. The CMJs with the greatest flight times were retained for analysis. Participants rested at least 2 minutes between CMJs. All CMJs were performed on a uniaxial force plate sampling at 1000 Hz. Mean and peak forces during the braking and propulsive phases were analyzed, with the braking phase defined as the point on the force-time curve where body mass is reached to where center of mass velocity reaches zero. The propulsive phase was defined as starting at the end of braking and ending at take-off. JH was calculated from flight time. Yank-time data was derived from force-time data using a low-pass Hamming filter with a 10 Hz cutoff frequency. Paired samples t-tests compared performance between CMJs with and without arm swing for the following metrics: PY, JH, mean (MBF) and peak braking force (PBF), mean (MPF) and peak propulsive force (PPF), and durations of the braking (BPD) and propulsive phases (PPD). Hedges’ g effect sizes assessed magnitude of effect. Pearson product-moment correlations assessed the relationship between PY and JH in both conditions (p< 0.05). RESULTS: With arm swing, greater JH (44.8±11.9 vs 35.3±8.9 cm, p< 0.001, g=2.5), PY (9848.1±2854.7 vs 7130.4±2125.6 N×s^-1, p=0.015, g=1.1), and propulsive forces (p=0.004-0.017, g=1.0-1.4) were observed. However, no differences in braking forces (p=0.47-0.64, g=0.16-0.26), BPD (p=0.21, g=0.46), or PPD (p=0.26, g=0.41) were observed. PY shared a stronger correlation to JH in CMJs without arm swing (r=0.91, p=0.002) than with arm swing (r=0.77, p=0.03). In jumps with arm swing, MBF, PBF, MPF, and PPF were stronger predictors of JH than PY (r=0.83-0.85, p=0.01). Strong correlations between JH and force measures were observed in CMJs without arm swing (r=0.81-0.91, p=0.002-0.02). CONCLUSION: PY was related to JH in CMJs with and without arm swing. However, PY is a stronger predictor of JH in CMJs without arm swing. This may indicate that the arm swing negates some of PY’s contributions to JH, and that alternate mechanisms explain performance differences in CMJs with and without arm swing. As force measures better predicted JH with arm swing, this may indicate that the arm swing motion significantly contributes to the ability to generate force in similar, time-limited windows. PRACTICAL APPLICATION: PY and force measures were significant predictors of JH, though their contributions differed between jump types. Coaches can use this information in testing and programming CMJs. If improved JH is desired, understanding mechanisms that contribute to JH for different jumps can influence the training prescription to improve performance.

Acknowledgements: None