Butt Wink in the Squat: What It Is and How to Fix It
2 min read
“Butt wink” is the small backward tuck of your pelvis at the very bottom of a squat. A little is normal; a lot under heavy load is worth fixing. Here's why it happens and what actually helps.
What butt wink is
At the bottom of the squat the pelvis rotates under (posterior pelvic tilt) and the lower back rounds slightly. You'll see the hips “tuck” right at the deepest point.
Does it matter?
A small amount right at the bottom is normal and, for most people at moderate loads, nothing to worry about. Research hasn't shown that the lower back bending while you lift causes back pain on its own, though the evidence is limited (Saraceni 2020 (opens in a new tab)).
It's worth fixing when it's large, repeated and happening under heavy weight. That means you've gone past the depth you can control today, and a tuck that grows with the load makes the bottom position harder to own.
Why it happens
- Limited ankle or hip mobility.
- Squatting deeper than your current mobility allows.
- A stance that doesn't suit your hips.
- Losing your brace at the bottom.
How to fix it
- Squat to the deepest point where you can hold your pelvis — don't chase rock bottom before you can keep position.
- Adjust your stance: a little wider, toes turned out a little more.
- Work on your ankles, or raise your heels slightly while your range improves.
- Brace hard before you descend and keep it through the bottom.
- Box squats to a box at your controlled depth make that depth repeatable.
The self-test in Squat depth explained will show you whether ankles, hips or bracing set your limit.
Check it on video
Butt wink is hard to feel, and it happens side-on. Film an extra set from the side at hip height and watch your pelvis at the bottom.
FormLens doesn't auto-flag butt wink yet, and its squat analysis is filmed front-on, which isn't the angle for seeing a pelvic tuck. What your front-on FormLens clip does give you is depth on every filmed rep, left/right knee balance and an obvious heel lift, which feed your form score — see squat depth explained, and how to fix knees caving in if your knees drift too.
How FormLens measures this
Squat · Filmed front-on, phone at hip height
- Depth
- Your lowest knee angle on each rep. Under 90° counts as reaching depth; the set is flagged when most reps stop short.
- Left/right balance
- The difference between your left and right knee angles at the bottom. 10° or more flags a rep.
- Heel lift
- Checks the bottom of each rep for an obvious heel lift, read from one foot, and shows how many reps it caught. Small rises aren't flagged.
- Stance
- Stance width (as a multiple of your shoulder width) and foot flare (toe-out), read from your setup.
- Consistency and tempo
- How closely your reps match each other, and how steady your rhythm is, on multi-rep sets.
Checking butt wink: it happens side-on, and FormLens analyses squats front-on — film an extra set from the side and watch your pelvis at the bottom.
Not auto-flagged yet: knee cave, butt wink and back angle. Front-on, depth reads conservatively — the knee angle can read higher than it really is. Every measurement is an estimate from a single camera, so setup matters — see the camera setup.
Sources
- Saraceni N, Kent P, Ng L, et al. To flex or not to flex? Is there a relationship between lumbar spine flexion during lifting and low back pain? A systematic review with meta-analysis. J Orthop Sports Phys Ther. 2020;50(3):121–130. View study (opens in a new tab)
Educational only — not medical advice. FormLens is a training aid, not a medical device; measurements are estimates from a single camera. If something hurts, see a physio or doctor. Terms of Use
First published · Last updated · By FormLens