RSI Test (Reactive Strength Index, drop jump)

What this is

The RSI Test is the seeded run-domain assessment that measures Reactive Strength Index — a single number that captures how well an athlete can absorb a landing and rebound into a jump. Useful as a neuromuscular readiness marker (fatigued athletes drop their RSI 10-20% from baseline) and as a long-term run economy proxy.

Domain: run. Estimated duration: 22 minutes. Linked calculator: rsi.

The 3-step protocol (as seeded)

1. Warm-up (15 min): dynamic mobility, plyometric prep (skips, low pogos, two-foot hops).
2. Drop Jumps (5 min): three drop jumps from a fixed box height (typical 30 cm; can also use 20 / 40 / 60 cm for force-velocity profiling). Land and rebound as quickly and as high as possible.
3. Record Data (2 min): note ground contact time and flight time for the best of three jumps (the one with the highest jump height).

Inputs the form asks for

Both inputs are in milliseconds (ms) — that's the native unit jump-mat hardware (Optojump, Force-decks, etc.) reports.

• Ground Contact Time (ms) — typical range 80-250 ms. Faster athletes are in the 100-150 ms range; novices and fatigued athletes drift longer.
• Flight Time (ms) — typical range 300-700 ms. Higher jumps = longer flight time.

If your jump mat reports in seconds, multiply by 1000 before entering (e.g. 0.150 s → 150 ms).

Outputs

• RSI (unitless) — computed as Jump Height (m) / Ground Contact Time (s). Typical ranges:
  • 0.5-1.0: novice / fatigued
  • 1.0-1.5: trained
  • 1.5-2.5: well-trained / sprint-trained
  • 2.5+: elite jumper / explosive athlete
• Jump Height (cm) — back-solved from flight time via h = g · (t/2)² · 100 where t is flight time in seconds (i.e. h = g · t² / 8, with t in seconds).

The math uses seconds internally — the form converts ms to s on submit. The unit label on the inputs stays ms because that's what the measurement device reports.

What RSI tells you

• Above baseline → fresh, well-recovered.
• Below baseline by 10%+ → fatigued, deload candidate.
• Trend rising over a block → plyo / sprint adaptation.
• Trend falling over a block → unintentional overreaching.

Pair with weekly wellness checks to disambiguate neuromuscular fatigue from other forms of fatigue (sleep, illness).

How often to test

• Weekly as a fatigue / readiness marker — same box height, same warmup, same time of day.
• Quarterly as a chronic adaptation marker — possibly across multiple box heights for force-velocity profiling.

Common gotchas

• Box height varies between tests — RSI scales with box height. Pick one and stick with it.
• Time of day varies — RSI is lower in the morning.
• Insufficient warm-up — without plyo prep, the first jump RSI is artificially low.
• Reporting flight time as airborne-feet time — some systems report contact-to-contact; others report toe-off- to-landing. Confirm which your device emits.

See also: Assessment model overview.