Drop Jump (RSI)
Step off a 30 cm box, land, and immediately rebound. Measures Reactive Strength Index.
30 cm is what most sport-science research cites as the intermediate default. Go lower if you're new to plyo or have knee sensitivity. Go higher only when you can keep ground contact under 250 ms at 30 cm — otherwise you're just thudding.
Tip: RSI is only comparable within the same box height. Pick one and stick with it for tracking.
What it measures
You step off a 30 cm box, land, and immediately jump as high as you can. The app measures how long your feet were on the ground (Ground Contact Time) and how high you rebounded. RSI = jump height / GCT — high RSI means you turn impact into elevation fast.
Why it matters
RSI is the gold-standard plyometric metric in sport science. Two athletes can jump the same height — one with 0.18s ground contact (elite) and one with 0.40s (a grinder). Coaches use RSI to identify athletes whose nervous system uses the stretch-shortening cycle efficiently. Improving RSI transfers directly to sprint speed and change-of-direction.
How to do it
- 1Pick the box height below (~30 cm recommended, lower if new to plyo, higher if advanced). Find a stable platform of that height — step, bench, or stacked plates. No wobble.
- 2Set your phone 2 m to the side, lens at hip height. Make sure your full body is visible.
- 3Stand on the floor first — full body in frame. The app calibrates the floor level.
- 4When prompted, climb onto the box. Voice says 'Drop off when ready'.
- 5Step off (don't jump off). Land with both feet, then immediately jump as high as you can — minimize ground time.