Reactive Strength Index
Reactive Strength Index and Elastic Rebound Capacity · Also known as: RSI, stretch-shortening cycle, elastic response
The reactive strength index (RSI) is a measure of lower-body reactive strength and elastic energy utilization, calculated as jump height divided by the contact time between landing from a drop and takeoff. Introduced by Bobbert and colleagues (1987), RSI quantifies the efficiency of the stretch-shortening cycle (SSC)—the ability to rapidly switch from eccentric (lengthening) to concentric (shortening) muscle contractions. High RSI indicates rapid, forceful engagement of muscles' elastic properties (tendons, contractile proteins) and is relevant in sports requiring rapid rebound (sprinting, jumping, rebounding). RSI is trainable and sensitive to plyometric training.
Read the full method
Sign in with a free account to read this section.
Method map
The neighbourhood of related methods — select a node to explore.
When to use it
RSI testing is valuable for athletes in sports requiring rapid rebound (sprinting, jumping, agility). RSI is particularly useful for monitoring plyometric training response and detecting neuromuscular fatigue (fatigued athletes have reduced RSI). Drop height should be selected based on athlete ability (20-50 cm range typical). Assumes proper landing technique to avoid injury.
Strengths & limitations
- Specifically targets stretch-shortening cycle capacity; not captured by concentric-only tests like CMJ
- Sensitive to plyometric training; RSI responds quickly (2-3 weeks) to SSC-specific training
- Relevant to explosive sports; high RSI correlates with sprinting and jumping performance
- Quick to administer and interpret; single number captures reactive capability
- Can detect acute fatigue; reduced RSI indicates CNS fatigue or recovery need
- Drop height significantly affects RSI; different heights produce different values, limiting comparisons
- Proper landing technique is critical and difficult to standardize; technique variations confound measurements
- Injury risk if not performed with proper instruction; excessive drop heights or poor landing can stress knees
- Reactive strength is partly genetic; limited improvement ceiling in some individuals
- Does not directly predict sport-specific reactive demands (lateral agility, field deceleration, collision impact)
Frequently asked
What is an optimal RSI value?
RSI is highly individual and depends on drop height. Typical values range 1.5-3.0 m/s; elite jumpers exceed 3.0. RSI improves 20-40% with targeted plyometric training. Compare individual RSI to their baseline, not absolute norms.
How does drop height affect RSI?
Higher drops increase landing impact and eccentric demand, but excessively high drops allow excessive braking (long contact time), reducing RSI. Optimal drop height varies by individual; typically 30-50 cm for trained athletes. Use athlete's preferred height or standardize across a group.
Can reactive strength be trained?
Yes, significantly. Plyometric training (box jumps, bounds, depth jumps) increases RSI within 3-4 weeks through neuromuscular adaptations (improved SSC coupling, tendon stiffness). Conversely, detraining or high aerobic work reduces RSI. SSC-specific training is necessary; strength work alone does not improve RSI.
Is RSI relevant for non-jumping sports?
Yes. RSI indicates overall elastic properties relevant to sprinting acceleration (ground contact time), agility (deceleration and direction changes), and any activity requiring rapid rebound. RSI declines with fatigue and age, making it a useful general readiness marker.
How reliable is RSI measurement?
RSI test-retest reliability is moderate to good (ICC 0.70-0.90) when drop height and instruction are standardized. Reliability improves with practice and proper technique. Always familiarize athletes with the test before collecting data for monitoring.
Sources
- Bobbert, M. F., Huijing, P. A., & van Ingen Schenau, G. J. (1987). Drop jumping. II. The influence of dropping height on the biomechanics of takeoff after landing. Medicine & Science in Sports & Exercise, 19(4), 339-346. DOI: 10.1249/00005768-198708000-00004 ↗
- Flanagan, E. P., & Comyns, T. M. (2008). The stretch-shortening cycle training in sport. Strength & Conditioning Journal, 30(6), 32-39. link ↗
- Taube, W., Leukel, C., & Gollhofer, A. (2016). How neurons make us jump: the role of the motor cortex in stretch-shortening cycle movements. Exercise and Sport Sciences Reviews, 44(1), 4-11. link ↗
How to cite this page
ScholarGate. (2026, June 3). Reactive Strength Index and Elastic Rebound Capacity. ScholarGate. https://scholargate.app/en/sports-science/reactive-strength-index
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- Counter-Movement JumpSports Science↔ compare
- Force-Velocity ProfileSports Science↔ compare
- Rate of Force DevelopmentSports Science↔ compare