Is Butt Wink Inevitable? Part 2

How the Spine Experiences Damage and Modifying Your Program to Prevent Injury (or to Adapt to Greater Stress)

In the first article titled “Is Butt Wink Inevitable?”, I discussed this oft-talked about movement pattern, how it is damaging to your spine, how it is inevitable for some folks, and why it may not even be a huge deal.

Butt wink occurs during the squat when there are issues with mastering technique, with hip and ankle mobility, or possibly if one’s hip sockets are too deep. Hip socket cannot be readily changed, unfortunately. Because butt wink forces the spine out of alignment whilst supporting heavy loads, it increases the amount of stress the back experiences. This increases the likelihood of injury. However, there are examples of the spine withstanding enormous loads in a flexed position WITHOUT injury occurring. The back, like almost any other part of our body, can adapt to varying degrees of stress.

But how can we quantify various movements and loads in terms of how much it damages our backs, and how can we apply this to our programming?

God Damn Spinal Flexion

As it’s been said time and time again, rounding your back during the deadlift or squat is considered bad. Because butt wink is essentially rounding your back, this point is relevant to our discussion. But why is it actually bad?

Reason #1 Why Rounding is “Bad”: Pinching of the Spinal Disk.

Of all the injuries the back can experience, disk bulges seem to be fairly prominent. According to the American Academy of Orthopaedic Surgeons, a significant percentage of people experience sciatica due to disk herniations.

I discussed in the last article that a neutral posture allows the spine to distribute force more evenly across the spinal disk. When the spine is taken out of neutral (into flexion or extension), there is more force on one side of the disk than the other side. A basic understanding of physics explains why this would injure the spinal disk.

Imagine you’ve got a table, a hammer, and a nail. If you hammer the nail into the table, the nail will punch right through. Try hammering the table without the nail, using the same amount of effort. What do you think will happen? Well, you might damage the table a little bit, but your sure won’t drive the hammer through the table like you did with the nail. Why’s that, you think?

When you swing a hammer at a table, your applying force onto the table distributed over the space of the hammer-head’s surface. All of that force is applied to an area the size of a U.S. quarter. With the nail, that same amount of force is applied to a much much smaller area. The smaller the area of impact, the more of an effect the force has on the structure. To be able to drive the hammer through a table, you’ve got to use way more force.

Butt wink

Like hammering a nail into your spine.

Compare this scenario to your spinal disks. When force is applied evenly across the disk, the structure holds up. When the spine begins to flex, the force is applied to a smaller area over the disk, acting like a hammer and a nail. That’s why disk bulges happen on one side – because one side of the disk is being attacked. If enough force was applied to a spine in neutral posture to injure the disk, the disk would completely burst. That’s just like swinging the hammer really hard at the table – you’d leave a large hole. This makes spinal injury while in a neutral posture less likely.

Reason #2 Why Rounding is “Bad”: Under-Activation and Shear Force

When you apply force to an object top-down, such as stepping on a soda can, this is known as compressive force.  When you apply force to both sides of an object in opposite direction, such as ripping paper into two pieces, this is known as shear force.

In the context of human movement, compressive force will happen to your body during the top of a deadlift – when your spine is simply being squished. Shear force will happen at the bottom of a deadlift – when your spine is being yanked on one side by the force of the barbell, while it is being yanked in the other direction by the supporting structures.

Butt wink

Shear vs compression.

In Dr. Stuart McGill’s Ultimate Back Fitness, a few studies are discussed that tell us a few things about the spine. The spine found in the average male can withstand around 3000 lbs of compression, while the spine of a competitive weightlifter can withstand over 4500 lbs of compression. Compare this to the amount of shear it takes to bust a disk in a cadaver spine, which is anywhere from 450 to 630 lbs. Assuming the spine of a cadaver is similar in strength to the spine of an average living male, a human spine can handle 5-10 times more compression than shear.

So, deadlifts are harder on your back than farmer’s carries, it seems… What does this have to do with back rounding? Well, Dr. Stuart McGill examined shear loads on the lower back, as well as muscular activity, in participants assuming the position of the bottom of a deadlift. I believe it was with an unweighted barbell, and participants rounded their backs as well as kept them neutral. What McGill observed was that the muscles of the core and back were hardly activated when the back was rounded, yet fired up when the back was in neutral.

Additionally, he observed that shear force of the neutral lower back was about 200N, or 45 lbs. Meanwhile, shear force of the rounded lower back was 1900N, or 430 lbs. This may explain why McGill observed that the muscles of the torso hardly activated while the spine was flexed. The muscles didn’t do their job, and the passive structures bore more of the load.

Butt wink.

A picture from the McGill study.

To summarize, the spine is much more prone to injury when facing shear force (AKA the bottom of a deadlift). A flexed spine will experience up to 10 times more shear than a neutral spine. Not only that, a flexed spine bears more load through it’s ligaments, disks, etc. because the muscles fail to activate and support the load.

It should be clear now why spinal flexion while under load is considered “bad”.

Round-Back Endeavors Don’t Kill Everyone, and What Doesn’t Kill You Makes You Stronger

In my last article, I mentioned that the Atlas stone event is popular in strongman competitions, and involves a heavily-rounded back to perform. There is a definite risk of injury in the sport of strongman, but strongman athletes aren’t dropping like flies. They are built like tanks and can take a beating. Check out Brian Shaw, for example, who lifted an Atlas stone weighing 550 lbs. He appeared to walk away from that lift intact and uninjured.

So what’s the deal with back rounding, then? Spinal flexion under load, particularly under shear load, is incredibly riskier than when in a neutral position, as we’ve established.

The Main Reason Why Back Rounding Isn’t Always Bad: The Human Body Can Adapt to Almost Anything, It Seems.

The Stress-Adaptation Model (pictured below) explains how stress, such as exercise, leads to an adaptation, such as increasing strength. First, there is the initial stressor, known as the stimulus. Immediately, there is recovery, or compensation. If the stress was large enough, there will be an adaptation, or supercompensation. Too much stress, and your body fails to recover properly; injury results and time off is needed to recover. Too little stress, and your body doesn’t sense a need to adapt; this is how you get some guys who have been benching 135 lbs for a year.

Butt wink.

The Stress-Adaptation Model.

Additionally, this Stress-Adaptation Model can be depicted in the short-term, or long-term. The picture and the prior explanation was of the long-term. In the short-term, you have a set amount stress you can handle before becoming injured. Let’s say the time period is within 24 hours. If you do a heavy deadlift workout successfully and leave the gym without pain, you have not passed that short-term threshold for injury. Over-time, that threshold for injury increases. However, the very next day, your threshold for injury has been lowered, because you’ve yet to recover. Repeating the same heavy deadlift workout the next day would be risky because it may be beyond your injury threshold.

Let’s say for that first heavy deadlift workout, you decided to double the sets that you originally planned to do. You go home feeling achey and wake up the next day with back pain. You pushed yourself beyond your short-term injury threshold.

You want to stress your body just enough.

If you can deadlift 600 lbs with a flat back, deadlifting 65 lbs with a rounded back should not injure you. Because you’ve used efficient technique, the shear loads on your spine were minimized, thus you were never injured. Because the weight constantly went up, the shear loads, although as small as they can be, increased, and your spine adapted to that. Thus, your spine is much stronger than it once was, and it will be prepared to lift light loads with a rounded back.

This is how strongmen can lift Atlas stones injury-free. They’ve all got massive deadlift numbers. Most likely, they’ve had decent deadlifts before training for strongman. Because their backs were already pretty strong, they were ready to train the Atlas stone lift and continue to adapt from there. Had they attempted training for Atlas stone lifting earlier on, their risk for injury would’ve been higher because they’re backs weren’t as durable. This scenario is an example of training within your injury threshold and continuously adapting.

Now, remember when I said that Dr. McGill observed that the torso muscles didn’t activate when the spine was flexed? Hypothetically, one can argue that the muscles of the back and torso can activate more as someone practices rounded-back lifts. Given how much more shear the spine experiences when rounded, it’d be impressive to say that one can lift an Atlas stone simply because their spine has adapted to insane amounts of shear force.

If the muscles were to adapt and activate more, the stress on the disks, ligaments, bones, etc. of the spine would experience a bit less stress because the muscles are now doing their job. Sure, there’s still the issue of disks being pinched, but at least some of the stress is being dealt with by the muscles.

Increased muscle activation is reason why the human body produces more strength (muscle hypertrophy is responsible as well). In fact, neural factors (AKA muscle activation) has been observed to be the primary reason for initial strength gains when starting a new program (Moritani, Toshio). Plus, muscular activation can improve post-surgery (Berth et. al), when muscular activation drops below baseline. Is it totally obscene to say that muscular activation can improve ABOVE baseline, as in the case of round-back lifting? I think not.

Practical Takeaways, Programming, and Exercise Selection

Now it’s time to finish up this article on and learn how to apply these ramblings and thoughts to training.

Scenario #1: The Lifter Has Butt Wink That Cannot Be Fixed.

Assuming one has done absolutely everything to “fix” butt wink, it may be because of  deep hip sockets that squatting below parallel is impossible without butt wink. By everything, I mean trying different back squat techniques (by changing stance-width, toe-position, low-bar vs. high-bar, different acceptable depths, etc.), improving hip mobilty and ankle mobility, and improving core stability and back strength.

Anyway, if butt wink is “unsolvable”, yet there isn’t back pain, one should keep training as usual. If one moves up conservatively and cautiously, avoids pain, deloads every couple of weeks, and avoids pushing to 100% failure regularly, the spine may very well adapt to the repeated bouts of flexion and butt wink without a hitch.

Because the squat technique (and possibly deadlift) is a bit more stressful on the trainee’s back than it normally would be, being a little more cautious would not be a bad idea. Enjoying progress, being diligent, and not being stupid will take a lifter far without injury. Now, if someone DOES have back pain, then things get a little more complicated…

Scenario #2: The Lifter Has Back Pain.

If someone gets back pain or an injury from deadlifts and back squats, the obvious solution is to take time off, reduce the weight and volume, and slowly build back up again over the period of days/weeks/months. How long depends on the severity of the injury.

If someone has back pain AND butt wink during the squat (and possibly deadlift), and cutting back the weight may not cut it. This is because the spinal flexion during every rep more damaging to your spine than when neutral.

If it’s already confirmed that cutting back the intensity and volume of back squats and deadlifts hasn’t helped  back pain, one can do away with back squats and deadlifts in the mean time. Front squats should be much friendlier to the back while still training a similar movement pattern as the back squat. The torso is more upright which reduces shear. Also, it requires less hip mobility. This means someone who has butt wink in the back squat may not have it in the front squat especially if their ankle mobility is fine.

As back pain subsides and someone wants to improve back strength and the posterior chain, RDLs will help out a lot. Obviously RDLs target the back, hips, and hamstrings, but they require less hip range-of-motion than deadlifts, while still lowering the torso to near-parallel. Hip socket depth will not cause one to round or have butt wink in the RDL. In the deadlift, because the knees are bent, the back will have to flex to reach it. RDLs never force your spine to flex. They have someone lower the bar as far as the hips allow, and that’s it. Thus, the RDL is great for strengthening the back in a more predictable manner.

Now, if one’s front squat and RDL has improved remarkably, and pain has been gone for a while, it may not be so risky to test the deadlift and back squat at the end of a training cycle before a deload. It’s like training for a meet. The body gets much stronger and is injury free, so the trainee wants to “test” his or her new strength. The meet is stressful on the body, but once it is over and new personal records are set, there is rest and recovery.

Attempting the deadlift and back squat occasionally while training with the front squat and RDL will minimize the risk of injury if butt wink is persistent. Now, if the deadlift and back squat has continually improved painlessly using the RDL and front squat, it is up to the trainee whether or not to transition into regularly training those two lifts again. Obviously it will be more stressful on the back, but as it’s been said before, the back can adapt to a lot of abuse.

Scenario #3: The Lifter Wants to Train Rounded-Back Lifts

Let’s say the lifter wants to train for strongman. Great. Among all the events to be trained for is the Atlas stone event, which has already been understood as tough on the back. But we know it can be done without injury.

Anyway, the safest approach to preparing for the Atlas stone event, in my opinion, would be to become strong in the deadlift. Even for those who need a small amount of butt wink or rounding the reach the bar, the deadlift will be easier on the back than an Atlas stone lift (assuming weights are equal). Just because one can deadlift 300 lbs doesn’t mean one can safely lift a 300-lb stone. Now, if one can deadlift 500-lbs, round-back lifting 50 lbs would pose little risk. In McGill’s study looking at shear forces, spinal flexion increased shear times 10. Hence, if one can deadlift 500 lbs, a 50-lb round-back lift shouldn’t be enough to bust up the spine.

A conservative way of training rounded-back lifts is to first try a set or two once a week at the lowest weight possible. This is, of course, once the lifter’s deadlift is respectable that weight used in the round-back lift is laughably light. Each week, add a set. After a few weeks, increase the weight used in the last set. Each week, increase the weight of one set. Eventually, the lifter will have one light set, and a couple sets at a slightly heavier weight. Keep adding weight to all sets but the lightest and one other. Then all but two, and all but one, assuming 5 sets are used. Then, eventually the lifter will hit a point where the sets are ramped. For example, 45 lbs – 55 lbs  – 65 lbs – 75 lbs – and then a final set at 85 lbs.

The spine and back muscle should adapt over-time, and eventually the lifter can push the weight and volume more aggressively. Boom. A strongman is made.

In Conclusion – That’s It with Butt Wink

The spine preferably takes a beating when it’s in a neutral posture, because flexion can turn spinal disks into popped balloons. However, the spine can adapt if one is careful. Folks with butt wink may not have to worry anymore, and people wanting to train strongman need not fear of inevitable injury.


1. McGill, Stuart. Ultimate back fitness and performance. Backfitpro Incorporated, 2009.

2. Moritani, Toshio. “Neural factors versus hypertrophy in the time course of muscle strength gain.” American Journal of Physical Medicine & Rehabilitation 58.3 (1979): 115-130.

3. Berth, Alexander, Dietmar Urbach, and Friedemann Awiszus. “Improvement of voluntary quadriceps muscle activation after total knee arthroplasty.” Archives of physical medicine and rehabilitation 83.10 (2002): 1432-1436.

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