Is Butt Wink Inevitable? Part 1

Got Low Back Pain? Do You Have Butt Wink During Squats? Your Parents May Be Partially Liable

Back pain is one of the most common injuries in America. Anyone who doesn’t live under a rock knows this. Apparently, approximately 31 million Americans experience back pain at any given time (Jensen M et. al).

For those in the iron-game, this reality is as apparent as ever. Lifters regularly support heavy loads with their backs, mistakes happen, and lumbar-related aches appear. Most of us would rather get injured occasionally than be scrawny and weak, so that’s okay. ‘Tis the life of being strong.

Anyway, conventional wisdom dictates rounding your back while squatting/deadlifting/etc. is hazardous to your spine. This idea has “birthed” a topic that’s been discussed ad nauseam by bodybuilders, powerlifters, and strength athletes alike. This topic is butt wink.

Butt Wink… Apparently Your Whole Butt Can Flap Like an Eyelid, and People Love to Talk About It

When you squat, if you experience some tucking of your tail (or slight flexion of the lower back) at the bottom of the lift, you are exhibiting what is known as “butt wink”. Because this is an example of back rounding, although very slight, many people worry whether or not this phenomena will screw up their lumbar spine.

Some of the usual causes for butt wink during the squat include poor hip mobility, poor core stability, poor spatial awareness and kinesthetic sense, and a lack of experience with the squat technique.

butt wink

I wonder if the Porifera twerk team is worried about back pain. Dat ass though.

Back rounding, and subsequently butt wink, are some of the most talked about causes of back pain. However, it’s been long-debated whether or not the small amount of spinal flexion in butt wink is a legitimate cause of back pain. Is it truly something to worry about?

To answer this question, I must refer to Dr. Stuart McGill, renowned spine biomechanics researcher from the University of Waterloo. McGill has done plenty of research regarding the spine and spinal injuries. An example of his work includes a study in which he and others found that repetitive low-intensity cycles of flexion-extension (think: 1000s of crunches) caused disk herniation in healthy pig spines (McGill et. al).

McGill takes the position that spinal flexion¬†when under load is to be avoided. Actually, he has responded to the whole butt wink debate and re-asserted the notion that “butt wink = spinal flexion, and spinal flexion under load = bad”. Here’s the interview in which he discusses this. Skip to 1:34 to get to McGill’s response.

When the back rounds, or when there’s butt wink, the spine goes out of alignment and “tilts” towards one side, causing each inter-vertebral disk to be slightly “pinched” on that respective side. The spine typically distributes forces evenly across each disk when under load if the spine is neutral. But if the spine is flexed, the side of the “pinched disks” will experience more force, and herniations can occur.

So, to answer the question – yes, butt wink is a legitimate cause for back pain. While butt wink is talked about all the damn time, one potential cause of butt wink – and back pain – is not.

Hip Socket Depth Will Determine How Well You Can Squat – and No One Talks About It

In the interview, Dr. McGill mentions how depth of the hip socket will affect how much hip flexion someone can perform. The deeper the hip socket is, the earlier the thigh bone and pelvis come into contact during hip flexion. While people try to fix butt wink by working on hip mobility, fidgeting with their squat technique, practicing squats over and over, strengthening their core, and etc., hip socket depth is never addressed.

In the squat, the hips, knees, and ankles must flex in unison to lower the body, and extend in unison to raise the body. Stop one of these joint while dropping into a squat, and you’ll either: a) lose balance, b) stop and rise back up, or c) flex the spine to get deeper into the squat.

butt wink

Left: deep hip sockets. Right: shallow hip sockets. The guy on the right won the genetic lottery for squats.

So, let’s say your hip sockets are particularly deep, meaning you have less range-of-motion for hip flexion. In the squat, you may very well not have enough hip flexion to squat below parallel without making it up somewhere else – i.e., your back with butt wink.

For certain people, their hip socket depth makes butt wink inevitable. They will be able to squat and deadlift only when some butt wink occurs.

Are Certain People “Not Built” to Back Squat and Deadlift?

Because squats and deadlifts require a maximal amount of hip flexion to get into the bottom position, any restriction in the hips will force butt wink and back rounding. So, if certain people with deep hip sockets simply cannot achieve a neutral spine throughout those two lifts, is back pain a certainty for these unlucky lifters?

Well, we know that spinal flexion under load is more stressful to the spine’s disks. Flexion is like a multiplier for stress on the disks when squatting and such. The neutral spine is the safest way to lift heavy weights.

The body can adapt to a certain amount of damage before it becomes too much to handle. Stress the body too much, and it weakens and gets injured. Squatting with a neutral spine, while using progressive overload, is the safest and most predictable way to keep the spine healthy and strong. When the spine flexes during the squat, you get an unpredictable “spike” in stress on the spine.

Curing joint pain.So, those with crappy hip socket depth will experience more stress than usual from squats and deadlifts. Does that mean those with unshakable butt wink should stop performing those lifts, or else risk injury? Well, not really.

The body can take a pounding and adapt to anything if the conditions are right.

As much as it seems that butt wink can be an easy cause of back pain, with its spinal flexion and all, it isn’t so cut and dry. Just take a look at strongman competitors. They lift with rounded backs all the time. Check out their stone lifting event. It’d be impossible to lift those atlas stones without rounding the back at all. Sure, there are injuries in strongman, but people make it through and can lift 400-pound stones.

butt wink

Rounded back – clearly not suffering from ruptured spinal disks.

Strongmen use the most efficient technique possible and train their spines to withstand the damage. Result? We get to watch the atlas stone lifting event each year on World’s Strongest Man, and the competitors walk out alive.

Everyone Has Butt Wink

Watch someone do the back squat. Actually, watch everyone who back squats. Look online for videos if you have to. What you’ll notice is that almost everyone has some degree of butt wink during a back squat with decent depth. Until there’s hard evidence that everyone who back squats will end up with a back injury, it’s arguable that the spine can and will adapt to the stress of slight flexion.

They key is identifying how much butt wink one experiences and to note if the back has already been injured. Then, one must monitor and modify training accordingly to make sure there isn’t too much stress on the spine to prevent injury. The right amount of stress is needed for adaptation. Exercise selection, intensity, frequency, technique, etc. all will alter the amount of stress.

In the next article, we’ll discuss how to modify your training according to those parameters, even if butt wink is inevitable. You can become awesome at the back squat and deadlift, despite your hip socket depth and amount of butt wink you experience. There’s no need to get mad at your parents.

So, is butt wink truly inevitable? For some people, improved technique and mobility will fix this “error” seen in the squat. As for other, their hip anatomy will always cause some degree of butt wink during the squat.

P.S. – If you want to learn more about spine health and biomechanics as they relate to athletics performance, pick up a copy of Dr. Stuart McGill’s Ultimate Back Fitness. In it, you’ll learn tons of theoretical and practical information about keeping the spine healthy while getting strong as hell. Enjoy.


1. Jensen M, et al. Magnetic Resonance Imaging of the Lumbar Spine in People Without Back Pain. N Engl J Med 1994; 331: 69-116.

2. Stuart M. McGill et. al. “Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force.” Clinical Biomechanics 16.1 (2001): 28-37.

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