The intraday reliability of the Reactive Strength Index calculated from a drop jump in professional men's basketball.
OBJECTIVE
To evaluate the reliability of the Reactive Strength Index (RSI) and jump-height (JH) performance from multiple drop heights in an elite population.


METHODS
Thirteen professional basketball players (mean±SD age 25.8±3.5 y, height 1.96±0.07 m, mass 94.8±8.2 kg) completed 3 maximal drop-jump attempts onto a jump mat at 4 randomly assigned box heights and 3 countermovement-jump trials.


RESULTS
No statistical difference was observed between 3 trials for both the RSI and JH variable at all the tested drop heights. The RSI for drop-jump heights from 20 cm resulted in a coefficient of variation (CV)=3.1% and an intraclass correlation (ICC α)=.96, 40 cm resulted in a CV=3.0% and an ICC α=.95, and 50 cm resulted in a CV=2.1% and an ICC α=.99. The JH variable at the 40-cm drop-jump height resulted in the highest reliability CV=2.8% and an ICC α=.98.


CONCLUSIONS
When assessing the RSI the 20-, 40-, and 50-cm drop heights are recommended with this population. When assessing large groups it appears that only 1 trial is required when assessing the RSI variable from the 20, 40-, and 50-cm drop heights.
Centre for Exercise and Sport Science Research, Edith Cowan University, Joondalup, Western Australia.
William J
WJ
Markwick
Stephen P
SP
Bird
James J
JJ
Tufano
Laurent B
LB
Seitz
G Gregory
GG
Haff
D000328:Adult; D056352:Athletes; D054874:Athletic Performance / Q000502:physiology*; D001490:Basketball / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*