Paul T. Donahue, Lindsey Legg, Hunter Haynes, Megan Rush. University of Southern Mississippi, Hattiesburg, MS.

BACKGROUND: The countermovement vertical jump (CMJ) is an exercise commonly used to monitor an individual’s neuromuscular abilities. Jump height is the most commonly used variable when discussing jumping ability. This provides a gross performance metric of one’s ability, yet fails in explaining the explosiveness of an athlete as a given jump height can be achieved using differing neuromuscular strategies. This has led to the more thorough analysis of the CMJ to better understand an athlete’s explosive muscular qualities. One such variable is the reactive strength index modified (RSIm) which accounts for the kinetic outputs of the tasks (jump height) and temporal constraints that are seen in sport. Thus, the purpose of this investigation was to compare groups of high and low RSIm performers to determine what variables may contribute to the explosive qualities in collegiate female athletes. METHODS: 42 female Division 1 collegiate athletes completed two maximal effort countermovement jumps as part of their athlete monitoring program. Prior to completing testing, each participant completed a standardized dynamic warm up. Each trial was separated by thirty seconds. All trials were performed on the same portable force platform, sampling at 1000 Hz. The mean of the two trials was calculated for each variable. Groups were determined as being above or below the median RSIm (0.38) for the entire sample. Group comparisons were made using independent t-test for each of the variables of interest. RESULTS: Significant differences were seen in RSIm (0.42 ± 0.05 vs 0.32 ± 0.4) and the high RSIm group having shorter eccentric duration (548.7 ± 77.62 vs 509.72 ± 53.07 ms). Though not significantly different, a moderate to large effect sizes was seen when comparing time to take off (d= 0.55) and jump heights (d = 1.22) between groups with the high RSIm group having greater jump heights and a shorter duration of time to takeoff. CONCLUSIONS: As RSIm is calculated as the ratio of jump height over time to take off (movement initiation to point of takeoff from the ground), the difference between individuals with high RSIm values appears to be a combination of achieving greater jump height and doing so in less time as neither showed statistically significant differences between groups.

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