Modified Reactive Strength Index (mRSI)
Target≈0
jump height ÷ time-to-takeoff, from a countermovement jump (CMJ).
Why this matters
mRSI adapts RSI to a CMJ, which starts from standing (no prior ground contact). It replaces contact time with time-to-takeoff (the contraction time from the start of the dip to leaving the ground), so it rewards a powerful, well-timed countermovement — not just how high the athlete jumps.
How it's computed here
From three marked frames: movement start → takeoff → landing.
- time-to-takeoff (TTT) = takeoff − movement start
- flight time = landing − takeoff
- jump height = 9.81 × flight_time² / 8
- mRSI = jump height ÷ time-to-takeoff
Capture requirement
TTT is longer than a drop-jump contact, but takeoff/landing timing still needs precision. Use ≥120 fps slow-motion; the tool warns when the clip is too coarse.
What good looks like
A committed, fast countermovement that converts into height — neither a slow grind nor a shallow dip with little output.
Coaching cues
- "Down fast, up faster."
- Pair with max-strength work when mRSI is limited by force, not speed.
Related
- Reactive Strength Index (RSI) — the drop-jump version.
source · sports/performance/learn/mrsi.md