Measured, Not Guessed:
How the Vertical Jump
Is Actually Tested

Ask any athlete how high they jump and you will get a number. Ask where that number came from, and the room goes quiet. A wall touch two summers ago. A guess. Something a teammate said.

I've spent my whole coaching career around jump numbers — with contact mats, with Vertec, with camera analysis, in club gyms and national team halls. And the pattern is always the same: the athletes who know their numbers improve them. The ones who guess, stay where they are.

Why Measuring Is Half the Training

At CSKA Sofia, our women's squad improved their average vertical jump by 12% across one season. People ask what secret method we used. There wasn't one. We tested constantly, everyone saw their numbers, and the numbers created the effort. When a jump gets measured, a jump gets attention. Testing isn't the boring part before training — testing is training.

The second reason is less romantic: fatigue. Jump height is one of the most honest daily readiness signals we have. When an athlete's countermovement jump drops well below their normal level, the nervous system is telling you something — usually days before the athlete admits it. No questionnaire is that honest.

How a Jump Is Actually Measured

Almost every serious method comes down to the same physics: flight time. While you are in the air, gravity is the only force acting on you — so the time between takeoff and landing tells us exactly how high your centre of mass travelled. Longer flight, higher jump. Simple and beautiful.

One warning about flight time: it can be cheated. Land with your knees pulled up and the clock runs longer — the "jump" grows without you jumping higher. A good measurement system watches your takeoff and landing, not just the air time. A good protocol (more below) does the rest.

What I Use Now

I wanted force-plate-style information without the lab: something an athlete straps on in five seconds, that measures every jump of a session, at a rate fast enough to trust — and that I could verify myself. That became the Explosive Belt: a belt-worn sensor sampling 500 times per second, paired with an iPhone/iPad app, and validated jump-by-jump against slow-motion camera footage before I let any of my athletes train with it.

The belt reads the movement of your centre of mass — the same thing a force plate infers from the ground. Height, flight time, takeoff velocity, and the deeper metrics below, for every single jump, live.

Beyond Height: Reading the Jump

Height is the headline, but it is not the whole story. Two athletes both jump 45 cm — and they are completely different athletes.

mRSI (modified Reactive Strength Index) is jump height relative to the time it took to produce it. One athlete sinks slowly and grinds up: big jump, slow engine. The other dips fast and explodes: same height, twice the speed. In a game, where you rarely have time for a deep, patient countermovement, the second engine wins. Same height — different training priorities.

Eccentric and concentric velocity — how fast you drop into the countermovement and how fast you push out of it — show the strategy of the jump. When eccentric speed rises and height holds, the athlete is learning to use the stretch. When it falls session after session, I start asking about sleep and load.

How to Test It Right

Measure honestly, test consistently, and the vertical jump stops being a mystery. It becomes what it should have been all along: a number you own — and a number you can move.