Abstract
Jump testing to monitor athletic performance and development has become commonplace in the field of strength and conditioning. Verbal cues of jump tests, such as the drop jump, has significant effects on performance metrics and movement strategy. The purpose of this study was to use a force platform analysis to investigate landing depth and global flexion in the lower extremity joints at initial impact between cues to maximize jump height or minimize ground contact time. Another purpose of this study was to repeat previous investigations on the influence of cueing DVJs to maximize height or minimize ground contact time on the Reactive Strength Index (RSI). Thirty-nine Division I soccer players performed one DVJ (DVJ<sub>Height</sub>) for maximum height and another DVJ (DVJ<sub>Quick</sub>) for quickness. Differences in dependent variables were analyzed by Bayesian paired samples t-tests. RSI was greatest in the DVJ<sub>Quick</sub> condition (Mean<sub>diff</sub> = 0.36 ± 104 (95% HDI: .232, .492). Ground contact time was shorter with the DVJ<sub>Quick</sub> (Mean<sub>diff</sub> = -0.19 ± 0.028, 95% HDI: -0.224, -0.155). Jump height was less with the DVJ<sub>Quick</sub> (Mean<sub>diff</sub> = -0.033 ± 0.007, 95% HDI: -0.068,.0035). Landing depth decreased during the DVJ<sub>Quick</sub> (Mean<sub>diff</sub> = -0.093 ± 0.018, 95% HDI: -0.118, -0.066). Global flexion in the lower extremities at impact decreased with a DVJ<sub>Quick</sub> (Mean<sub>diff</sub> = -0.057 ± 0.025, 95% HDI: -0.084, -0.031). DVJ<sub>Quick</sub> resulted in a large increase in RSI due to disproportionate decreases in ground contact time (large decrease) compared to jump height (small decrease). The increase in RSI with DVJ<sub>Quick</sub> coincided with a decrease in landing depth, suggesting a stiff landing strategy and increased stretch-shortening cycle intensity.
Highlights
Jump testing to monitor athletic performance and development has become commonplace in the field of strength and conditioning
With regard to landing technique and strategy to accomplish these differences in performance, we hypothesized global flexion at impact and landing depth to decrease with the DVJQuick
This hypothesis was confirmed by a 0.093 m decrease in landing depth during the DVJQuick compared to the DVJHeight (Meandiff = -0.093 ± 0.018, 95% highest density intervals (HDI): -0.118, -0.066) with an effect size estimate of -1.69 (95% HDI: -2.27, -1.13)
Summary
Jump testing to monitor athletic performance and development has become commonplace in the field of strength and conditioning. Monitoring jump performance can be used to assess training program efficacy [18, 5], return-to-play decisions following injury [11], fatigue [19], athlete workload monitoring [26], and predict athletic success [7, 9]. The DVJ is suited for testing stretch-shortening cycle performance of the lower extremity [18]. One common metric to assess DVJ performance is the Reactive Strength Index (RSI). RSI is calculated as jump height divided by ground contact time during a DVJ, making it a time-sensitive measure of performance.
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