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Starting Strength in the Real World


“Butt Wink”

by Mark Rippetoe | August 09, 2018

back extension in the squat

Perhaps the most overused and annoying term in the limited vocabulary of inexperienced coaches, it was first used by CrossFitters who were trying to impress other CrossFitters with their mastery of the secrets of human movement. Since the first CrossFitters were skinny females, and since skinny females display lumbar extension better than they do almost anything, anybody not displaying excessive lordotic curvature at the bottom of the squat was guilty of the crime. As is usually the case, things are more complicated.

The strong, trained human spine is supported on all sides by muscle mass, and the stronger the back, the bigger the muscle mass supporting it. Normal anatomical position for the lumbar spine is referred to as extension, and the extended lumbar spine displays a concave-inward curvature. The lumbar musculature is primarily composed of the erector spinae group, whose function is the isometric stabilization of the spine under a load. Squats and deadlifts load this muscle group, which responds by growing bigger and stronger.

In fact, a strong man should have enough spinal erector muscle belly to fill the lordotic curve, to the extent that the lower back does not visibly display the entire extent of the lumbar vertebral curvature – and perhaps no curvature at all. I have seen strong men with a slight convexity in a perfectly extended lower back.

So the following points must be kept in mind: 

  1. Big erectors are a part of a big deadlift. Don't expect to observe a concave lumbar on a strong man.
  2. The glutes grow along with the erectors as strength increases. As the hips flex into the bottom of the squat, the glute bellies change shape as they stretch eccentrically, affecting the appearance of the hips in the below-parallel position.
  3. There is quite a bit of variability in the normal lordotic position of the human spine. Some people are fairly curvy, and some people are fairly flat in the same degree of normal anatomical extension.
  4. A little bit of spinal flexion under a load is not an anatomical catastrophe. The human spine, as you should have noticed, is quite tolerant of stupid positions – this is demonstrated by your brother-in-law every afternoon. A tiny bit of spinal flexion (unaccompanied by rotation, a much more serious problem) is absolutely no reason for a 50% deload and a trip to the gulag.
  5. Everybody must be taught the correct way to hold lumbar extension under a load. Some people will learn this faster than others, but everybody who lifts should be shown that lumbar extension is the correct position in which to use a loaded spine, and how best to keep it that way.

Wholesale lumbar flexion at the bottom of a squat or the start of a deadlift cannot be tolerated. It must be corrected early in the process of teaching the lifts. But running around yelling about “Butt wink!” or even “buttwink” is not a substitute for the experience necessary to both recognize an actual problem and correct that problem – especially when there may be no problem at all.


For more on lumbar extension under a load see:


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