Reactive Strength Index (RSI) Calculator
Measure elastic strength from jump height and ground contact time.
Reactive Strength Index (RSI) Calculator
RSI measures your stretch-shortening cycle efficiency — how fast you absorb a landing force and redirect it into a powerful takeoff. A key metric for plyometric programming, sprint development, and tracking reactive strength gains over time.
Measured from a drop jump or repeat jumping test.
Time from landing to takeoff in milliseconds.
Time airborne from takeoff to landing. Apps like My Jump 2 and PUSH Band output this directly.
Time from landing to takeoff in milliseconds.
RSI = jump height (m) ÷ ground contact time (s). A higher value means faster, more explosive ground contacts. For reliable measurement use a contact mat or force plate — smartphone apps like My Jump 2 can estimate jump height from video within ~10%. Track RSI across an 8-week plyometric block; a gain of 0.2–0.4 is a meaningful training adaptation.
About this calculator
RSI (Reactive Strength Index) is one of the most important metrics in athletic performance — it directly measures how quickly and powerfully an athlete can switch from absorbing a landing force to producing an explosive takeoff. This ability, called the stretch-shortening cycle (SSC), underpins sprinting speed, change of direction, and repeated jump performance. RSI is calculated as jump height ÷ ground contact time (m ÷ s): a higher number means faster, more powerful ground contacts. Elite sprinters and jumpers typically score above 2.5; recreational athletes commonly fall in the 1.0–1.8 range. It is best measured with a contact mat, force plate, or a validated smartphone app like My Jump 2.
How to interpret your results
RSI can be improved two ways: increase jump height, decrease ground contact time, or both — and tracking them separately tells you which quality to target. High jump height + long contact time signals weak reactive ability; focus on fast-transition plyometrics (hurdle hops, depth jumps with quick rebounds). Short contact time + modest jump height signals a power deficit; add strength and contrast training. The ideal RSI profile for most sports is short contact + moderate-to-high jump height. Test every 3–4 weeks at the start of a fresh session (never after warm-up or conditioning). A 0.2–0.4 unit gain across an 8-week plyometric block is a meaningful adaptation.
The science and formula
RSI = jump height (m) ÷ ground contact time (s). Jump height is derived from flight time: h = g × t_flight² / 8, where g = 9.81 m/s². Ground contact time is measured from landing to next takeoff. The stretch-shortening cycle (SSC) mechanism underlying RSI involves pre-loading musculotendinous units during landing, storing elastic potential energy, and releasing it during propulsion. The short SSC (contact time <250 ms) relies primarily on tendon elasticity; the long SSC (>250 ms) involves more active muscular contribution. RSI specifically measures short SSC efficiency — a quality strongly linked to sprint performance and change-of-direction ability.
Important limitations
RSI measurement requires accurate ground contact time, which is difficult to measure reliably without a contact mat or force plate. Ground contact time errors of ±20–30 ms significantly affect RSI calculations — a contact time of 180 ms versus 210 ms at the same jump height changes RSI by 17%. RSI is specific to the drop jump protocol and does not generalise perfectly to other expressions of reactive strength (e.g., bounding, cutting). Fatigue also affects RSI more than other power metrics — RSI should be measured at the start of training sessions, not after warm-up or conditioning work.
Frequently Asked Questions
What is a good RSI score?
RSI benchmarks vary by sport and measurement method. As a general guideline: below 1.0 is low; 1.0–1.5 is average; 1.5–2.0 is good; 2.0–2.5 is very good; above 2.5 is elite. Drop jump RSI values tend to be higher than other jump types due to the plyometric loading stimulus.
How do I improve my RSI?
RSI improves with plyometric training focused on minimal ground contact time — depth jumps, repeated hurdle hops, and reactive bounding. Contrast training (heavy lifting followed immediately by explosive jumps) is also effective. Progress by increasing drop height gradually and emphasising "land and immediately jump" cues rather than a soft-landing approach.
What tools do I need to measure RSI accurately?
A force plate is the gold standard but is expensive. Contact mats and timing systems (e.g., OptoGait, Myotest) are practical alternatives. Several validated smartphone apps using the accelerometer can estimate contact time and jump height within ~10% of force plate measures. Manual stopwatches are not accurate enough for RSI measurement.
How does RSI relate to sprinting speed?
RSI correlates strongly with 10 m sprint time (r = 0.70–0.80 in research). Athletes with high RSI are better at applying force during the brief ground contact phases of sprinting (contact times of 80–120 ms at top speed). Improving RSI through reactive plyometric training typically produces 2–5% improvements in 10–30 m sprint times.
What drop height should I use for RSI testing?
Research typically uses a 40 cm drop height as the standard for RSI testing. Some protocols use individualised optimal drop height (the height that produces the best RSI score) — typically 30–50 cm for most athletes. Higher drop heights increase loading on the Achilles tendon and require more advanced plyometric preparation.
Is RSI sport-specific?
RSI has highest relevance for sports involving frequent jumping, bounding, cutting, and sprinting — basketball, volleyball, soccer, rugby, track and field. It has moderate relevance for sports with some explosive demands but longer ground contact times (cycling, swimming, rowing). RSI is a reliable talent identifier in jumping and sprint-based sports and is used in athlete profiling by many national sports institutes.
How often should I test my RSI?
Test every 3–4 weeks during a plyometric training block. Always measure at the start of a session — before any warm-up sets, conditioning work, or fatigue accumulates. RSI is one of the most fatigue-sensitive power metrics; a single hard training session can suppress scores by 10–20%, so testing mid-block or post-workout will underestimate your true reactive strength.
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