Lunge: proper form and the mistakes the camera catches
The forward lunge trains one leg at a time: quads, glutes and the balance to control them. Here is how to do a lunge, and what the camera checks on each rep.
How to do a lunge
- Stand tall with feet hip-width apart and your core braced.
- Take a long step forward and lower your body straight down.
- Stop when both knees are bent to about 90°, front knee over the ankle, back knee just above the floor.
- Push through your front heel to step back to the start, then switch legs.
Engine thresholds · lunge
How the camera judges your lunge
The engine follows each lunge through the same five phases as a squat and compares your two knees at the bottom. A rep starts when the front knee bends below 158° and counts when it reaches depth and straightens again.
Depth: knee angle
≤ 85°
Left–right knee gap
≤ 22°
Errors checked
4
What the camera catches
Common lunge mistakes
Uneven legs at the bottom
One knee bends much more than the other, so the weight shifts to one side.
Trigger left–right knee angle gap > 22°
Fix: lower straight down between your feet, not onto the front leg.
Front knee caving in
The front knee drifts inward past the hip–ankle line.
Trigger medial knee shift > 0.10
Fix: keep the front knee in line with your second toe.
Not deep enough
The front knee never bends past the depth threshold.
Trigger knee angle stays above 85° (±5°)
Fix: lower until your back knee almost touches the floor.
Losing balance
The body sways sideways or the torso wobbles through the rep.
Trigger back angle swings > 10° or speed jumps 2× your average
Fix: take a slightly wider stance and slow the descent.
These are the thresholds the app uses for the lunge (its own rule set plus the general checks in the pose engine), exported from the app's code for this page.
Lunge questions
Should my front knee go past my toes?
A little is fine if your heel stays down. Keep the knee tracking over your toes rather than falling inward.
Forward or reverse lunge for beginners?
Reverse lunges are easier on the knees and balance. Once they feel steady, forward lunges add control work.
How many lunges should I do?
3 sets of 8–10 per leg with clean form is a good start.