New test
Pick how you want to measure.
Motion sensor test
- Strap the phone on. Use a tight belt at your waist, or press it firmly against the front of your hip. It must not move.
- Press Start. Stand tall with your hands on your hips and keep the phone upright.
- Wait for the low tone. The phone checks it is upright and steady, then calibrates for about 2 seconds.
- Jump on the high beep. One quick dip, jump as high as you can, land on both feet and stand still.
Camera test
- Stand the phone on the floor. Upright, 2 to 3 metres away, screen facing you.
- Face the camera. Both feet stay in view, which gives the most accurate result.
- Follow the voice. When you are in place with hands on hips, it counts down and records by itself. Jump on the beep.
The in-app camera records at 30 to 60 fps. For the sharpest timing, film in your camera's slow-motion mode (120 to 240 fps) and load the clip here.
Frame rate settings
Leave the factor at 1 if the clip plays at normal speed. If it plays in slow motion, enter how many times slower it is. For example, 240 fps played back at 30 fps is 8.
History
Your data
Results are saved on this phone only. Back up now and then, and before you switch phones or browsers.
Settings
Guide
How to do a good test
- Warm up for 5 to 10 minutes, including a few easy jumps.
- Keep your hands on your hips the whole time. Arm swing changes the result.
- Dip to whatever depth feels natural and jump straight away. Don't pause at the bottom.
- Keep your legs straight until you land. Tucking your knees makes the flight look longer.
- Do 3 to 5 jumps with 30 to 60 seconds rest. Look at your best and your average.
- For fair comparisons, test at the same time of day, in the same shoes, on the same floor, after the same warm-up.
Motion sensor or camera?
Motion sensor. The phone measures how your hips accelerate. Multiplied by your body mass, that gives a force curve like a force plate does, so you also get power, jump phases, dip depth and RSImod. It only works if the phone is strapped on tightly.
Camera. The app times how long you are in the air, frame by frame. This is the method used by validated apps such as My Jump (Balsalobre-Fernández et al., 2015). It is the most dependable way to measure height, especially with slow motion, but it can only estimate power.
What the numbers mean
Is my change real?
Every jump varies a little. CMJ Lab learns how much your own jumps vary from session to session, usually 2 to 5%. It only calls a change real when it is bigger than that, and never smaller than 3%.
Tiredness often shows up first in how you jump, not how high. You may take longer to leave the ground, and your RSImod and FT:CT ratio drop, while height stays the same (Gathercole et al., 2015).
Jump phases follow McMahon et al. (2018). Movement start uses a 5-SD threshold on quiet standing (Owen et al., 2014).
Limits of a phone
- A phone is not a force plate. Treat force and power as estimates and watch the trend over time.
- Hard landings can exceed what the phone's sensor can read, so landing force may be too low.
- Height from time in the air assumes you land in the same position you took off in.
- This is not a medical device. Stop if anything hurts.