Measurement agreement (repeatability) for a countermovement jump protocol using a portable forceplate.

This study assessed measurement agreement of jump-height measures derived from a portable forceplate sampling at 500 Hz. Female (n = 42) and male (n = 30) participants (total N = 72, age = 19.7 +/- 2.8 y, height = 174.5 +/- 9.3 cm, mass = 71.4 +/- 12.8 kg) performed 25 separate maximal jump attempts. This incorporated 5 sets of 5 single jumps. One min of rest was allowed between jump attempts, with a 3-min rest period between sets. For each participant, the best jump height for each set of 5 jumps was kept for analysis. No systematic bias was identified, and the best jump height was stable within participants across all 5 sets of jumps. Therefore, factors such as fatigue and learning did not affect the measures. Females did jump lower (P = or < .0001) than their male counterparts, justifying additional analysis of agreement for the 2 gender groups. Heteroscedasticity was found, so ratio limits of agreement (LOAs) were calculated by using the antilog of the log-transformed data. The calculated ratio LOAs were x// 1.08 for the total group, x// 1.08 for females, and x// 1.08 for males. From the calculated ratio LOA, the jump protocol was shown to provide stable measures of jump height. In addition, the ratio LOA can be helpful to interpret findings from research that report jump height derived from the same protocol and assessing participants from the studied population (ie, active university-age male, female, or combined-gender groups).