Why a butt wink isn’t a death sentence…
When we think of “good form” when squatting, we typically imagine a neutral spine as we move throughout the movement to avoid the butt wink.
What is a butt wink?
The butt wink is a movement pattern that occurs at the bottom of the squat, where the pelvis rotates backward. This backward motion, also known as a posterior pelvic tilt, is often associated with rounding of the lower back, also known as lumbar flexion.
This "good form" that we imagine, is a HUGE misconception - research tells us that to squat, there is indeed motion taking place at the spine, despite our best efforts to maintain a “neutral” position [1-4].
Multiple factors contribute to why the butt wink is more noticeable in some people than others including…
Squat Position
When it comes to your squat position, you may notice your back arching (lumbar extension) in an attempt to maintain a “neutral” spine as you descend - to squat well though, the opposite must occur. As you descend into the squat, your back will naturally move towards lumbar flexion and this is when we see the "butt wink." Because of this, we recommend avoiding an excessive arch, given the lack of benefit from doing so.
Joint mobility and how deep you descend into the squat
Joint mobility, at your hips and ankles, is also relevant when observing a butt wink. If you have less hip flexion range of motion and/or ankle dorsiflexion(the positions your hip and ankles are in at the bottom of your squat), you may notice more motion coming from your lower back as you descend to hit your desired depth.
These differences from person to person play a role in the butt wink - however, the degree of their impact is determined by the depth of your squat…The lower you go, the more low back and hip motion you will notice [2], to reach such depths.
“Is butt wink going to cause injury?”
First, where did the concern come from?
Research that investigates disc herniations showed that repetitive rounding and compression of the spine leads to disc herniations [5]. The problem with this research is that it was performed on cadaver pig spines that were exposed to 86,400 cycles of repetitive bending - those cadaver spines are not able to adapt like living human beings are and those repetitive cycles don’t simulate real-life scenarios that allow for rest and recovery for our bodies to adapt.
Another study [6] used different ranges of compressive loads, noting that disc herniations did not occur with loads above 30% compressive tolerance. Instead, the bones of the low back were stressed. This tells us that we can be confident that the bones of the low back and surrounding muscles are getting stronger [7,8] and adapting to the stimuli present, with good programming execution. Considering this information, we can confidently say that butt wink does not inherently demonstrate an increased risk of injury.
“What if butt wink hurts me?”
Chances are there was a time when you were butt-winking pain-free.
Keeping this in mind, we can use strategies that allow the area calm down as we build it back up. An easy low-hanging fruit for many of us is to lower the volume/intensity of training to see if that changes anything. If not, altering the depth of your squat or using a different stance - wider or elevating the heels - are options to consider to help you avoid sensitive positions as you recover.
Technique, depth, and mobility demands are all modifiable factors to consider to improve comfort during your squat.
Everyone’s body is different - everyone will have some degree of low back and hip motion during the squat, as it is a natural motion that occurs. With all things considered, we can see that the topic of butt wink is not as simple as “rounding back = bad”.
Citations:
Potvin JR, McGill SM, Norman RW. Trunk muscle and lumbar ligament contributions to dynamic lifts with varying degrees of trunk flexion. Spine (Phila Pa 1976). 1991;16(9):1099-1107. doi:10.1097/00007632-199109000-00015
Yanagisawa O, Oshikawa T, Adachi G, Matsunaga N, Kaneoka K. Acute effects of varying squat depths on lumbar intervertebral disks during high-load barbell back squat exercise. Scand J Med Sci Sports. 2021;31(2):350-357. doi:10.1111/sms.13850
Aasa U, Bengtsson V, Berglund L, Öhberg F. Variability of lumbar spinal alignment among power- and weightlifters during the deadlift and barbell back squat. Sports Biomech. 2022;21(6):701-717. doi:10.1080/14763141.2019.1675751
Edington C. Lumbar spine kinematics and kinetics during heavy barbell squat and deadlift variations. [Master's thesis]. Saskatoon, Saskatchewan: University of Saskatchewan; 2017.
Callaghan JP, McGill SM. Intervertebral disc herniation: Studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clin Biomech (Bristol, Avon). 2001;16(1):28-37. doi:10.1016/s0268-0033(00)00063-2
Parkinson RJ, Callaghan JP. The role of dynamic flexion in spine injury is altered by increasing dynamic load magnitude. Clin Biomech (Bristol, Avon). 2009;24(2):148-154. doi:10.1016/j.clinbiomech.2008.11.007
Conroy BP, Kraemer WJ, Maresh CM, et al. Bone mineral density in elite junior Olympic weightlifters. Med Sci Sports Exerc. 1993;25(10):1103-1109.
Tsuzuku S, Ikegami Y, Yabe K. Effects of high-intensity resistance training on bone mineral density in young male powerlifters. Calcif Tissue Int. 1998;63(4):283-286. doi:10.1007/s002239900527