How ShakeFit grades a rep

Most home workout apps count what you started. ShakeFit grades what you did. A rep that counts ends with a word on screen, and on most moves that word comes from how the rep actually went.

What the camera reads

The front camera watches you move, and a pose model inside the app turns each frame into the positions of 16 body joints: shoulders, elbows, wrists, hips, knees, ankles and feet. That is everything the app works from. There is no face in that set and there are no fingers, and the frame itself is discarded as soon as the positions are read. The camera does not keep the video covers that part in full.

From those positions the app follows one repetition from start to finish. For a squat that is the way down, the bottom and the way back up. For an overhead punch it is the reach and the return.

The grade words

Every rep that counts gets one of four words: PERFECT, GREAT, GOOD and COACH.

• PERFECT is your full range on that move
• GREAT is nearly your full range
• GOOD is a rep that counted, with room to go further or steadier
• COACH appears when the app sees the same form slip on two reps in a row

Range comes first, and it is your own range. The app calibrates a range of motion from your own first repetitions of a move, and grades the reps after that against it. Steadiness counts too, but only when the app has measured it: a wobbly rep can drop a grade, and a rep whose steadiness was not measured is graded on range alone.

A few more rules sit behind those words, and they are worth knowing because they shape how a track feels.

A rep that covers too little of that range is not graded at all. It does not count toward your reps, and it is not held against you: the combo stays where it was and the screen asks for a little more. There is no MISS.

A one-off slip stays quiet. The rep tops out at GOOD and nothing interrupts you. COACH only appears when the same slip repeats, so a single wobble never earns a correction. A COACH rep does not add to the combo, and two in a row reset it.

The app looks for a few large slips, and only on some moves. Where it has not measured your range, the rep is graded GOOD. It does not hand out a PERFECT for form it has not seen.

Timing never lowers a grade. The grade is about the shape of the rep. A graded rep that lands on the beat is marked ON BEAT. On moves that land or sway, such as the jumping jack and the grapevine, that mark also adds to the score. On the other graded moves it is shown and the score stays the same.

Graded moves and counted moves

Of the sixteen movements in the app, twelve are graded from your pose in the way described above. The other four are fast rhythm moves: Front kick, High knees, Knee up and Twist. Those are counted on the beat rather than read from your pose. Each beat-counted rep scores as GOOD and keeps the combo going, and the app does not judge its form or its timing.

Both kinds add to the same score, so a track can mix them freely.

Why grade at all

A count tells you that you showed up. A grade tells you how the rep went while there is still a next rep to do something about it.

It is also what turns a short track into a game. The combo climbs while reps keep landing, the grade words stack up, and the result screen at the end shows how many of each you earned. One more round starts to sound reasonable.

What a grade is not

A grade is a game score, not a medical assessment of your form. ShakeFit is entertainment and general fitness software. It is not a medical device and it does not give medical advice. If something hurts, stop.

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