Can your phone count your reps? How camera counting works

Counting reps sounds trivial until you're on rep nine of a hard set and can't remember whether it was nine or ten. A phone that counts for you, without anything strapped to your body, is now possible: small pose models can follow 33 points on your body in real time, right on the phone.

How camera rep counting works

The camera finds your joints in each frame and works out the angle that matters for the lift: your knee for squats, your hip for hinges, your elbow for presses, rows and curls, your shoulder for raises. A rep is counted each time that angle leaves your starting position and comes back. Smoothing filters stop a wobble or a blink of lost tracking from being counted as a rep.

Good counters do more than count. They also grade each rep: a partial rep that didn't reach most of your usual depth, a grinder that was much slower than the set's fastest rep or stalled on the way up, and a failed rep that didn't come back up.

Where to put your phone

1. Side-on, about two to three metres away, so your whole body is in the frame from head to feet.
2. At roughly hip height, propped on a bench, a plate or a water bottle.
3. Good light from the front or side, not a bright window behind you.
4. Check the dot. In Liftsmith a dot on the camera preview turns green when your whole body is in view.

What it can and can't count

• Back squatQuads, Glutes
• Goblet squatQuads, Glutes
• Push-upChest
• Standing overhead pressFront delts
• Dumbbell curlBiceps
• Dumbbell lateral raiseSide delts

Squats, lunges, presses, push-ups, rows, curls and raises all have a clear joint angle to follow. Holds like the plank, carries, shrugs and wrist curls don't, so the camera leaves those to you. Very cluttered gyms, baggy clothes and people walking through the frame can all throw it off.

Trying it in Liftsmith

Camera rep counting is in Settings › Labs, the Pro section for features we're still testing. Turn it on and a Count reps button appears on the exercise demo during a workout. While it counts, the 3D figure follows your movement, with the camera beside it and the bones it sees drawn over you. The reps it counts fill in the reps box, so logging stays one tap, and you can still change the number.

Tip: Your video never leaves your phone. Each frame is read in memory and thrown away, and the pose model is part of the app, so counting works offline too.