Guide

Can an app count my reps? How camera rep counting works, and when it doesn't.

Yes, a phone camera can count your reps and tell a deep squat from a shallow one. It is not magic and it is not perfect, and the difference between an app that is useful and one that is annoying is whether it knows which is which. Here is how it works in Loopform AI, in plain words, including the list of things that make it miss.

Step one: finding your joints

Every frame the camera sees, a pose-tracking model running on the phone finds the main joints of your body: shoulders, elbows, wrists, hips, knees, ankles, plus a few on the head and feet. Nothing is uploaded; the model is on the phone and the video stays there. What comes out is a stick figure, thirty or so times a second, with a confidence score on every point. That stick figure is the only thing the rest of the app ever looks at.

Step two: one angle per movement

A coach watching a squat is mostly watching the knee. The app does the same. Each movement has one primary joint angle: the knee for squats and lunges, the elbow for push-ups and presses, the hip for hinges and deadlifts, the whole body line for a plank. From the side view the app reads the side nearer the camera and never averages the two sides, because from the side the far arm or leg is hidden behind the near one and its points pile up in the wrong place.

Step three: what counts as a rep

The angle goes down as you go down and comes back up as you stand. A rep is one round trip, but with rules, because a camera also sees you shifting your weight, bending to grab a dumbbell, or losing a joint for a frame:

• A resting baseline. The app learns what "standing" looks like for you, at the top, and keeps adjusting it as the set goes on.
• A minimum drop. The angle has to fall a set amount below that baseline before anything is a rep at all. Shallower dips are thrown away: not counted, not criticised.
• A minimum time. Real reps take well over half a second. Anything faster is treated as noise.
• A clear finish. The rep completes when you reach the top again, or when you stop rising for a moment. So a set where you never fully lock out still counts, and the height you stop at becomes the new top.
• Lost tracking is not a rep. If the tracker loses a joint, the readings it produces are nonsense, and the app knows to ignore them rather than count them.

Depth is judged on the lowest point the rep reached. If it went deep enough, the rep is clean. If it was a real rep but short of the mark, it counts and the coach says something about it on the next one.

Step four: faults, called once

Knees caving, a back rounding, hips sagging: each is a line or an angle that went past its tolerance. The app does not call a fault from a single frame, because single frames lie. It waits until the fault has shown up for long enough in the rep to be real, then says one thing, in plain words, and moves on. The form-check guide lists what it watches on each movement.

When it misses, and why

• You are not fully in frame. The most common cause by far. If your feet or head are cut off, the angles are wrong. The coach says "step back" when it sees this.
• Wrong angle for the movement. Knees caving are invisible from the side; depth is unreadable from the front. The coach asks for the right view before each movement. The filming guide has the table.
• Light behind you. A window or a bright light behind you makes you a silhouette and the tracker loses your joints.
• Things in the way. A plate between you and the camera, a bench, another person walking through. Stand so the bar is on the far side of you on a deadlift.
• Mirrors. Two of you confuses the tracker. Face away from the mirror wall if you can.
• Very fast or bouncy reps. Below about half a second a rep looks like noise. Slow down a touch; your joints will thank you anyway.
• New movements. The six core patterns have been tuned on real sessions. The newer camera movements are marked beta in the app and the coach asks you to say the number if the count is off.

What it cannot see

The weight on the bar. Your spine itself, which has no landmarks, so a rounding back is read from the line of ear, shoulder and hip, deliberately conservatively. Anything in true three dimensions: these are angles in a flat image, which is why the camera position matters so much. Every cue is an estimate from a phone camera, and the app treats it that way: it counts your word over its own when you give it, and it never pretends to a precision it does not have.

Other apps make different trade-offs: some grade a video afterwards, some only judge depth, some never speak. AI form-check apps in 2026 lays them side by side.

Questions people ask

• Does it need the internet? No for the counting and the form cues: pose tracking runs on the phone and the phone's own voice can speak the cues. The conversational coach and the cloud voice need a connection and have a fair-use allowance.
• Front camera or back camera? Front, so you can glance at the screen between sets. Prop the phone up with the screen facing you.
• Does it count partial reps? No. A dip that stays too shallow is not a rep: it is discarded, not counted and not flagged. A real rep that is a little shallow counts, and the coach says so.
• Can it see how much weight I'm lifting? No. It sees your body, not the plates. Tell the coach the weight and it will remember it for the set.
• Does it work in a dark room? It needs light on you, in front of you. A window behind you turns you into a silhouette and the tracker loses your joints.
• What if the count is wrong? Say the number out loud and the coach takes your word. On the newer camera movements it asks you to do exactly that, once per movement.
• Where does the video go? Nowhere. Tracking happens on the phone and the video stays there unless you choose to share a clip.

Rep counting and form cues are free, with or without a subscription. Video never leaves your phone unless you share a clip. Android arrives in January.