The Pelvis & Low Back Relationship

Welcome back to Squat University! For the past few weeks we have been have been discussing the topic of low back pain during the squat. If you haven’t checked out our previous lecture articles, I encourage you to read them before moving on. The information shared will help give you a good foundation to understand the complexities of this current article.

Low Back Pain Table of Contents

Today we are going to move on to part four of our series and discuss the pelvis and low back relationship. This includes discussing the infamous “Butt Wink” and the exaggerated anterior pelvic tilt or “Instagram Model Squat”.

The Give & Take Relationship

When the low back moves, the pelvis moves. (1) For example, if the low back arches excessively, the pelvis will tip forward as well. In the opposite manner, if the pelvis tips backwards (called a posterior rotation) the low back will reflexively round or move into a flexed position.

During the squat, a small amount of movement in either direction is normal. Research has even shown that men and women will have different amounts of this movement during the barbell squat (2). This is usually attributed to differences in anatomy.

The width of your squat stance will also affect how much movement is seen at the low back & pelvis. Generally, a narrow stance will cause more movement to take place at this area compared to a wider stance (2). Let’s now talk about the two most common movements we see during the squat!

The Dreaded Butt Wink!

First, let’s start with a quick explanation of what “butt wink” is. The term refers to the posterior rotation or tipping of the pelvis during the descent of the squat. Unfortunately research is unclear at this time as to why this movement occurs. However, there are two popular theories we will discuss today.

Butt Wink.JPG

The first, and most popular theory, centers on anatomy. During the descent of the squat the thigh bone (femur) rotates in the hip socket (called the acetabulum). As the depth of the squat increases, the femur can eventually come into contact with the front rim of the socket. The timing of this contact will depend on the size of the femur and the depth of the socket. Because the femur can no longer rotate at this point, the pelvis must reflexively rotate backwards in order to continue the descent of the squat.

The second, and less understood theory on the cause of butt wink, is based on mobility (with the most convincing argument centering on the ankles). When the ankle becomes stiff and immobile (particularly in the movement of dorsiflexion) the knee will be unable to push forward over the toes during the deepest portion of the squat. This directly affects the position of your pelvis and low back (2-4). For example, in order to squat deep with stiff ankles, the pelvis will eventually pull under the body (posterior tilt) causing the low back to lose its stable neutral position.

So is “butt wink” really a problem? Unfortunately, there is no current research linking this movement with injury. We can only theorize. The current thought-process amongst experts is that excessive butt wink could cause a lumbar disc injury over time.

When the spine is locked in a stable position, it can handle tremendous forces. However, when excessive butt wink occurs compressive forces are not handled as well. The load from the barbell is transferred from the muscles and bones to the smaller structures in the spine (5). With many repetitions and with enough force (from the weight of the barbell) it is believed that this excessive motion could cause a herniation and a disc bulge injury over time.

Here is renowned back expert Dr. Stuart McGill speaking on the topic

 The “Instagram Model Squat”

We’ve all seen it. The girl dressed in next to nothing with her butt pushed out for all to see. While this movement may get you thousands of likes on social media, it’s not helping you squat at all.

Pelvis & Low Back.jpg

If you push your butt out and arch your low back, your pelvis tips forward excessively. Trying to squat weight in this position instantly places harmful forces on the smaller structures of the spine. Overtime, this over-extended position could cause a serious injury called spondylolysis (6,7).

Final Thoughts

Can butt wink and over arching your back during the squat cause an injury? Theoretically yes. However, I think the fear of these issues has been slightly blown out of proportion.

Excessive movement in EITHER DIRECTION is obviously not advised. However, if you’re an athlete who shows a little movement in either direction, it’s likely NOT AS BIG of a deal as many have made it out to be. To a point, some pelvic motion is normal depending on your anatomy. No amount of mobility or stretching is going to fix this.

Until next time,

Dr. Aaron Horschig, PT, DPT, CSCS, USAW


Kevin Photo
Dr. Kevin Sonthana, PT, DPT, CSCS


  1. Levine, D., & Whittle, M. W. (1996). The effects of pelvic movement on lumbar lordosis in the standing position. Journal of Orthopaedic & Sports Physical Therapy, 24(3), 130-135.
  2. McKean, M. R., Dunn, P. K., & Burkett, B. J. (2010). The lumbar and sacrum movement pattern during the back squat exercise. The Journal of Strength & Conditioning Research, 24(10), 2731-2741.
  3. List, R., Gülay, T., Stoop, M., & Lorenzetti, S. (2013). Kinematics of the trunk and the lower extremities during restricted and unrestricted squats. The Journal of Strength & Conditioning Research, 27(6), 1529-1538.
  4. Campos, M. H., Aleman, L. I., Seffrin-Neto, A. A., Vieira, C. A., DE Paula, M. C., & DE Lira, C. A. (2016). The geometric curvature of the lumbar spine during restricted and unrestricted squats. The Journal of Sports Medicine and Physical Fitness.
  5. Schoenfeld, B. J. (2010). Squatting kinematics and kinetics and their application to exercise performance. The Journal of Strength & Conditioning Research, 24(12), 3497-3506.
  6. Syrmou E, Tsitsopoulos PP, Marinopoulos D, et al. Spondylolysis: a review and reappraisal. Hippokratia. 2010 Jan-Mar; 14(1):17-21
  7. Letts M, Smallman T, Afanasiev R, et al. Fracture of the pars interarticularis in adolescent athletes: a clinical-biomechanical analysis. Journal of Pediatric Orthopedics. 1986;6:40-46

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