What the camera checks, exercise by exercise
GymSensei uses your phone's camera to count reps and catch form faults on 16 exercises. This page lists what it looks for on each one, with the angles it uses, so you know what a counted rep takes before you start.
How it works
Prop your phone up and start your set. The app tracks 13 points on your body (nose, shoulders, elbows, wrists, hips, knees and ankles) on the phone itself. The camera feed is never uploaded.
For each exercise it follows one angle through the rep, like your knee in a squat or your elbow in a curl. A rep counts only when that angle covers the full range and comes back. Stop short and you hear a cue such as "Go a little lower", and the half rep doesn't count.
Faults work the same way. One has to last 0.15 seconds before it counts, so a flicker in the tracking won't set it off, and you hear each cue at most once a rep. After the set you get a score and one line of advice about whatever went wrong most often.
It copes with real gyms, too. If baggy clothes or your build mean you never read as fully straight, it moves the starting point to where you are once you've stood still for a little over a second. If part of you is out of shot it tells you ("Step back so I can see your knees"), and on side-on exercises it asks you to turn if you're facing the phone.
The 16 exercises
| Exercise | What it checks | Film it |
|---|---|---|
| Squat | Depth and chest position | side-on |
| Push-up | Depth and a straight body line | side-on |
| Lunge | Depth and an upright body | side-on |
| Romanian deadlift | Hinge depth and knee bend | side-on |
| Overhead press | Full lockout and even arms | facing the phone |
| Biceps curl | Full range and elbow position | side-on |
| Plank | A straight line, head to heels | side-on |
| Glute bridge | Full hip lift and where your feet are | side-on |
| Sit-up | Full range, all the way up and back down | side-on |
| Lying leg raise | Leg height and straight legs | side-on |
| Lateral raise | Height and even arms | facing the phone |
| Bent-over row | Full pull and staying bent over | side-on |
| Jumping jacks | Arms all the way up and down | facing the phone |
| Pull-up | Chin over the bar and even arms | facing the phone |
| Wall sit | Thighs level with the floor | side-on |
| Side plank | A straight line, head to heels | facing the phone |
Plank, side plank and wall sit are holds: instead of counting reps, the clock runs only while you're in position.
Updated . General fitness and nutrition guidance, not medical advice.
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