In 2014, I herniated my L4, L5, and S1 because of my butt wink. That injury kicked off years of rehab, unlearning and relearning how to move—both as an athlete and a professional.

So what is butt wink, exactly? Is it inherently bad? Should you stop squatting if you have it? And how do you know if it’s happening to you?

I’m Annie Miller, certified strength and conditioning specialist, and I help you learn as you train so you can enjoy your lifts again without having to figure it all out yourself. Butt wink can be alarming. It causes fear for some, and real injury for others. Today, we’re making sense of what’s happening, what doesn’t cause it, and how to address it.

Prefer to watch instead of read? Click here to watch on YouTube.

What Is Butt Wink?

Butt wink most commonly shows up during squats—especially back squats or other bilateral squat patterns. It’s when your lumbar spine goes into flexion at the bottom of the squat.

I say “true” butt wink because not everyone who thinks they have it actually does. Sometimes, you’ll see the spine shift during the squat, but it’s just moving from an extended position to a neutral one. That’s not butt wink, even though it might still need some work.

Here’s how it typically looks: the tailbone tucks under at the bottom of the squat, then “pops” back up as you rise out of the hole.

You can think of your ribcage and pelvis like two bowls stacked on top of each other. Ideally, those bowls stay relatively parallel through the squat. Butt wink happens when that alignment breaks and the pelvis tucks under. That creates pressure and energy leaks out the low back, which is not ideal when you’re under load.

To be clear: your spine should be mobile. It’s meant to move. But there are more and less efficient paths for movement—and under load, butt wink is one we want to avoid.

What Doesn’t Cause Butt Wink

Let’s start with what’s not causing your butt wink.

Despite what you may have heard, it’s not your tight hamstrings or hip flexors. Anatomically, that just doesn’t add up. Your hamstrings change very little during the squat—they shorten at the knee and slightly lengthen at the glutes, but they’re not pulling the pelvis down. Hip flexors actually shorten as you descend into a squat.

So if those aren’t the culprits, what is?

What Does Cause Butt Wink

There’s no single reason for butt wink, but here are some common contributors:

• A weak or under-engaged core
• A weak or under-trained lower back
• Limited ankle mobility
• Squatting too deep for your current mobility level

Let’s break those down.

Weak or Under-Firing Core

Your core includes more than just your six-pack. It’s everything from your shoulders to your hips—and how well that system can create and maintain pressure.

If you can’t find or maintain a neutral spine through the squat, you’re more likely to lose connection between your upper and lower body. Try doing a bodyweight squat slowly. Can you stay braced? Can you hold tension at the bottom?

You don’t need to max-brace for every rep, but a “loosey goosey” core will almost always cause issues under load.

Weak Lower Back

A lot of people are scared to train their low back, but I’d argue it’s a weak link for many. If you’re contracting through your abs in the front but have no matching strength in the back, you may see pelvic instability—aka, butt wink.

Muscles like your erector spinae and quadratus lumborum are responsible for supporting that neutral position from the backside. They need to be strong, but also trained in the squat pattern, not just in isolation.

Limited Ankle Mobility

If your ankles don’t have enough range of motion, your body will find it somewhere else—often in your lower back. That’s where the pelvis starts tucking and the spine begins to flex.

Try a squat with a slightly wider stance or toes turned out. That might create enough room to reach depth without the compensation. You can also test your ankle mobility by checking whether your knees can travel 4–5 inches past your toes while keeping your heel on the floor. Most people can get by with 3.5 inches, but it’s individual.

Squatting Too Deep for Your Current Mobility

This is a big one. You might simply be squatting deeper than your body can control right now. And no, not everyone needs to go ass to grass under load.

Use video analysis. Film yourself from the side and look at where the butt wink starts. If it happens well before parallel, that’s more concerning. But even if it shows up just below parallel, you can make a small adjustment. Stop just before the wink, and work from there while addressing the underlying cause.

For more help with squat mechanics and depth, you might also like:
How Neutral Spine Did Me Wrong

So… Does It Matter?

Yes, butt wink matters. But no, it doesn’t mean you’re broken or guaranteed to get hurt.

It’s just a sign that something needs attention. Whether it’s your core, your low back, your ankles, or your squat depth—there’s something that can be trained and improved. You can lower the load, change your stance, or stop just shy of your usual depth as you build better movement patterns.

Most importantly: don’t fear it, but don’t ignore it either. You have options.

Want help fixing it? Head over to The Ultimate Guide to Fix Your Butt Wink for drills, breathing tips, and accessory exercises that actually work.