Force-Time Analysis of the Drop Jump: Reliability of Jump Measures and Calculation Methods for Measuring Jump Height

The purpose was to evaluate reliability of measurements during drop jump (DJ) and magnitude of differences in vertical jump height (VJH) when calculated using two variables: time-in-the-air and center-of-mass velocity. Thirty-seven handball players performed three single-leg and double-leg DJs on a portable force plate during two sessions. Sixteen outcome measures and four sets of reliability metrics, including intraclass correlation coefficients (ICCs), were estimated. All outcome measures, except vertical time-to-stabilization, yielded high (0.70-0.89) to very high (0.90-0.96) interday and intraday ICCs for the single-leg and double-leg DJ tests. These results indicated that the single-leg and double-leg DJ tests can be considered reliable for short-term and long-term monitoring of collegiate handball players of both sexes. In addition, the single-leg DJ VJH calculated using these two variables differed in magnitude (mean difference in test measurements: 0.64 cm, p < .001, effect size: 0.165). Therefore, we recommend using the same method to calculate single-leg VJH for long-term monitoring.