(41) THE RELATIONSHIP BETWEEN DROP JUMP REACTION FORCES AND THE MEASURES OF FORCE DEVELOPMENT IN THE ISOMETRIC MID-THIGH PULL

The assessment of lower-body athletic performance characteristics is imperative for effective training in various sports, as measures of both strength and power are indicative of athletic progression. The measure of the reactive strength index (RSI) refers to the ability to quickly change from the braking phase to the propulsive phase during the drop jump (DJ). Previous research has found an association between this explosive force and the rate of force development (RFD) outputs generated by the lower limbs. As RFD may not always be linear, an effective assessment tool is the isometric mid-thigh pull (IMTP), assessing RFD at different epochs or time intervals. However, there is a paucity of research examining RFD during IMTP for various epochs and their relationship to RSI.

Purpose: To determine the correlation between RFD in IMTP at different epochs and the RSI during DJ.

Methods: Thirty NCAA Division I collegiate-level athletes (n = 9 basketball, n = 21 track athletes) participated in this cross-sectional study. Each athlete performed two to three trials of DJ from a 45.74 cm high box with a subsequent one to two-minute rest period between trials. Following the DJ, two trials of the IMTP were performed. All athletes performed the DJ and IMTP trials on two force platforms at a sampling rate of 1000 Hz. The best trials of each test were used for analysis. The force-time variables calculated from the IMTP were the rate of force development (RFD) during specific epochs of 0-50ms, 0-100ms, 0-150ms, 0-200ms, and 0-250ms. The variable of interest during the DJ was RSI. The Pearson r coefficient was used to evaluate the relationship between RSI and IMTP RFD epochs. The significance level for all analyses was set at p < 0.05.

Results: Athletes’ mean ± standard deviation (SD) RSI performance on the DJ was 1.59 ± 0.61. The mean ± SD duration of total DJ contact time (duration of concentric and eccentric phases) was 256 ± 10 ms. A significant positive correlation was found between 0-250ms IMTP RFD and RSI (r= 0.431, p= 0.017). Contrarily, there was no significant correlation between RSI and IMTP RFD 0-50ms (r= 0.163), 0-100ms (r= 0.150), 0-150ms (r= 0.340), and 0-200ms (r= 0.350), (p > 0.05).

Conclusion: Our findings suggest that a longer epoch of RFD IMTP is associated with RSI as measured during the DJ. This can be partly explained by the similarity in total DJ contact time and the duration of RFD during IMTP near the 250ms mark. PRACTICAL APPLICATION: Assessing RFD may be most meaningful over longer epochs, for example at 250ms during IMTP to provide the best insights into an athlete’s force generation capacities that are most relevant to explosive movements such as drop jumps.

Acknowledgements: None