Jump & reactive strength
Enter the times you measured (contact mat, photocells, force plate) and get jump height, reactive strength indices and the optimal drop height for that individual athlete. Times in seconds, heights in centimetres.
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From flight time. The CMJ starts from standing with a countermovement; the SJ starts still, in a half squat, with no countermovement.
Enter the mean values of the best 5 repetitions (out of 10 maximal rebounds, hands on hips, contact as short as possible).
One trial per drop height. The optimal height is the one where RSI peaks while contact stays short.
How to read the indices
RSI (Reactive Strength Index) = jump height ÷ contact time: how much height you produce for every instant spent on the ground. The higher it is, the better the fast SSC. It only makes sense with short contacts (< 0.25 s); beyond that the jump becomes a "slow" one and the index is no longer comparable.
DRI (Dynamic Rebound Index) = (drop height + jump height) ÷ (9.81 × contact time²): a dimensionless alternative to RSI that also accounts for the eccentric load (the height you drop from). In the 10/5 test the drop height coincides with the rebound height.
Optimal height: in the incremental drop jump it is the drop at which RSI peaks. Beyond it, contact time lengthens more than the jump grows and reactivity falls: that is the intensity ceiling for that athlete.
- Height from flight time — Bosco C., Luhtanen P., Komi P.V. (1983), Eur J Appl Physiol.
- Reactive strength / RSI — Young W. (1995), New Studies in Athletics; Flanagan E.P., Comyns T.M. (2008), Strength & Conditioning Journal.
- Test 10/5 (10-5 Repeated Jump Test) — Harper D.J., Hobbs S.J., Moore J. (2011), BASES; reliability: Comyns T.M. et al. (2019), Int J Sports Physiol Perform.
- Optimal drop height — Byrne P.J., Moran K., Rankin P., Kinsella S. (2010), J Strength Cond Res.
- DRI (Dynamic Rebound Index) — Brooks L.C. (2026), European Journal of Sport Sciences 5(1):1-10, doi:10.24018/ejsport.2026.5.1.9272 — a dimensionless alternative to RSI, sensitive to drop height.