Comparing drop jumps with 10/5 repeated jumps to measure reactive strength index

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Callum Stratford with Thomas Dos’Santos, and John J McMahon

The reactive strength index (RSI) indicates how efficiently an athlete can utilise the stretch shortening cycle. Our study aimed to compare RSI values between the 10/5 repeated jumps test (RJT) and drop jumps (DJs) from 30 (DJ30) and 40 cm (DJ40). Thirty males (age = 23.97 ± 5.94, height (m) = 1.80 ± 0.08 and mass (kg) = 81.14 ± 11.66) from multiple sports performed three trials of the DJ30, DJ40, and 10/5 RJT on a force platform, in a randomised order; ground contact time (GCT), jump height (JH) (derived from flight time), and RSI were compared between tasks. RSI derived from the RJT demonstrated excellent reliability and acceptable variability (intraclass correlation coefficient (ICC) = 0.975 and coefficient of variation (CV) = 6.3%). RSI from the DJs also showed excellent reliability but slightly greater variance (ICC = 0.946 – 0.929, CV = 8.2-11.2%). Repeated measures analysis of variance (RMANOVA) revealed no significant differences (p = 0.540, d = 0.14) in RSI between the RJT and DJs (r = 0.551-0.848) and only shared 30% common variance (r2). Large and small significant differences in GCT (p < 0.001, d = 1.45- 1.54) and JH (p =0.010, d = 0.50-0.54) were observed between the RJT and DJs, respectively. Due to the low shared variance in RSI between the RJT and DJs, we suggest that the jumps cannot be used interchangeably to assess RSI, and that an athlete’s reactive strength qualities are taskdependent.

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