Reactive Strength Index (RSI) is computed as jump height (m) ÷ ground contact time (s) from a drop jump. It indexes the athlete's ability to switch from an eccentric (landing) phase to a concentric (jumping) phase quickly and powerfully — exactly the action that decides sprinting, cutting, and rebound jumping in sport.
Typical RSI values: elite sprinters 3.0–4.0, NCAA male field sport 2.0–3.0, untrained adults 0.8–1.5. The cue for athletes is "jump as high as you can, on the ground as briefly as possible" — high RSI requires both.
Box height matters: most labs default to 40 cm so RSI numbers compare across athletes. Higher boxes shift the test toward absolute strength; lower boxes shift it toward true reactive ability.
Where it's used
Sprint and plyometric program design, return-to-play decisions after lower-limb injury, talent ID for explosive sports.
References
- Schmidtbleicher D (1992). Training for power events. In: Strength and Power in Sport (Komi, ed.).
Back to the glossary
Browse the full sport-science glossary for related terms.