Jump metrics — Docs

Open any rep on its summary and Metric Jump shows the numbers that rep supports. A countermovement jump gets height, velocity, RSI-modified, impulse and flight time. A repeat jump test gets RSI, contact time and hop height. A drop jump gets height, contact time and RSI. The table shows which metric applies to which jump.

Metric	CMJ, Abalakov, single-leg	Squat jump	Repeat jump	Drop jump
Jump height	Yes	Yes	Hop height	Yes
Takeoff velocity	Yes	Yes	No	No
RSI-modified	Yes	No	No	No
RSI	No	No	Yes	Yes
Contact time	No	No	Yes	Yes
Impulse	Yes	Yes	No	No
Flight time	Yes	Yes	Yes	Yes

Jump height

Jump height is the headline number. It is how high your centre of mass rises from a standing start. Metric Jump derives it from your takeoff velocity. This is the same calculation a force plate uses.

Because height comes from takeoff velocity, not from time in the air, tucking your legs on landing does not raise it. On a jump mat or in a flight-time app, that tuck stretches the flight time and does raise the number.

Metric Jump also shows your height as a percentage of your personal best, live, after each rep.

Takeoff velocity

Takeoff velocity is how fast your body moves the instant you leave the ground. It is not the same as peak velocity, which comes a moment earlier, while your feet still push. Metric Jump reads it straight from your centre-of-mass motion at takeoff.

RSI-modified

RSI-modified is the reactive strength number for a countermovement jump. Metric Jump divides your jump height by the time from the start of your dip to takeoff. Two athletes can jump the same height. The athlete who gets there in less time scores higher.

Watch RSI-modified and height together. An athlete can hold their height by sinking into a deeper, slower dip. Their height stays flat while RSI-modified falls.

RSI (repeat jumps and drop jumps)

RSI is a different number from RSI-modified. Metric Jump divides a hop’s height, in metres, by the contact time on the floor before it, in seconds. On a repeat jump test, your test RSI is the mean of your scored hops. See Repeat jumps & hops for which hops score. On a drop jump, the contact runs from landing off the box to takeoff, and the height comes from the rebound’s flight time.

The two numbers measure different things and sit on different scales, so compare each one only with itself.

Contact time

Contact time is how long your feet stay on the floor between two hops, in milliseconds. Metric Jump times it from your feet. A repeat jump test reports the mean contact time of your scored hops. A drop jump reports the one contact between the box landing and the rebound.

Hop height

Hop height is how high each repeat jump hop takes you. Metric Jump works it out from your time in the air: height = g × T² ÷ 8, where g is gravity and T is the flight time.

Jump height avoids this flight-time method. Hop height can use it because a repeat jump hop is too short for a tuck. Pull your feet up and you lose the bounce, and your contact time and RSI show it. Metric Jump times takeoff and touchdown from your toes and heels, filmed side-on.

Impulse

Impulse is the mechanical cause of the jump. It is the net force you applied multiplied by the time you applied it. Impulse is what launches you. Metric Jump works it out from your takeoff velocity and the bodyweight on your profile. If your bodyweight is out of date, impulse is wrong by the same share.

Flight time

Flight time is how long you are in the air, from takeoff to landing. On a jump, Metric Jump reads it from your centre of mass, not from a contact mat. On a repeat jump hop or a drop jump rebound, flight time is the input to height.

Comparing jumps in a set

When a set holds more than one jump type, Metric Jump compares them. The paired scores are eccentric utilisation, L / R balance, arm swing contribution and bilateral index. A repeat jump recording with a left and a right test adds L / R balance on RSI. See Jump analytics.