“Butt wink”, such a fancy term deserves to be explained by the pure logic at least. First and foremost, “butt wink” occurs only during deeper flexion movement of both hips at same time (bone to bone contact). But the depth where it occurs is individual because our hip complex anatomy is individual (with majority of people it starts to occur when thighs reach parallel-to-ground position). Someone believes that’s happening because of short/stiff hams, someone because of hip/pelvis anatomical issues. First, take a look at the video below (it’s a very simple explanation by the one very famous coach).
Maybe I am wrong, but anatomical issues (acetabulum and femoral head with surroundings anatomy) make sense more to me, especially because lower attached parts of hams are shortened during the knee flexion (which is the case in the squat for sure), so there is nothing to contribute to “butt wink” (if we know where is hams attachment on the pelvis – 2 joint muscles who don’t change its length during squat because lower part is shortening while upper lengthening during lowering phase of squat). I mean, I found recently that there is a small amount of lengthening although, but I think it does not contribute to “butt wink”: “In the eccentric phase of the squat, the hamstrings are simultaneosly lengthened by the act of hip flexion and shortened by the act of knee flexion, because they are both hip extensors and knee flexors. Until recently, it was therefore believed that the 2-joint hamstrings did not change length at all in the squat. However, one study reveals that there is a small amount of lengthening (albeit nowhere near as much as for the quadriceps), probably caused by anterior pelvic tilt.” – Chris Beardsley. Is it the coincidence that “butt wink” happens during deadlift (more extended knees comparing with squat), but ONLY in the case of “deadlift with deficit” variant (I don’t mean on anatomically not gifted for a bit more serious “hip hinge”)? Worth thinking…
The better option is front squat because of more upright torso, or split squat – “Bulgarian split squat” is even better because split legs position makes “butt wink” doesn’t happen (hip extension – rear leg is always making a counterbalance). Or lunges, step up…
“Butt wink” is more dangerous when your back is under a load or relatively relaxed on bench (leg press is a good example in the second case). In the first case, bigger negative (compressive) low back forces are produced by low back muscles comparing with bodyweight squat, and in the second case spine ligaments could be damaged. Low back spine needs to be in a stable – neutral position during full ROM to prevent a low back injury (especially when back is under a load with back squat or deadlift with deficit – or from the floor with some people).
Plus, who has anterior pelvic tilt (APT) “butt wink” will occur earlier – bone to bone contact comes earlier during lowering phase of squat for example (makes sense). That’s the reason why some people need exercise modification when it comes to squat and deadlift, or any other exercise with deep hip flexion requirements (“Sumo” deadlift or squat is good version – spread legs more and toes out, so thighs can come aside a bit during lowering phase). Of course that you can do squats without going to deeper position (reduced ROM), or you can do rack pull, both effectively – but I am talking only about finding some modifications when it comes to executing with almost full ROM because the effect is greater when it comes to “full muscle development” (what’s more SPORT specific is another topic). Assisted glutes stretching (when one is at supine position) needs modification also (move his/her leg aside more, not pure hip flexion because one could feel pinching at front hip – especially someone who got APT).
Plus, who got poor ankle dorsiflexion ROM (mobility) “butt wink” could happen earlier during lowering squat phase because one needs to lean torso more forward to prevent falling back (need for balance), which is simple explained in the video above (example for classic back squat). Plus lower back suffers from greater load in that example. That’s why I prefer more front squat, goblet squat… (poor ankle dorsiflexion needs to be fixed for sure). “Butt wink” will occur a bit earlier during back squat because torso is leaned forward more compared to front squat, and shins stay more vertical (it means an earlier “crash” between femur and pelvis).
PS: Don’t get me wrong, “butt wink” is not a big deal if it shows up during bodyweight squatting (or under some really small load) and during slow ecc. muscle contraction. In opposite, shear and other forces are high.
From the mechanical standpoint, the perfect solution for people who suffer from poor ankle dorsiflexion and early “butt wink” occurring is TRX squat with straight arms forward and KB squat with straight arms forward (a bit less). But that exercises are stupid (except for warming up) because you can’t load yourself in first case and let’s try to hold weightier Kettlebell longer in front of you with straight arms in second case 🙂 . Good solution is lifters heels but it’s not good for knees when go too forward, and posterior chain muscles (glutes, hams…) are less active in that case. But don’t worry, nobody needs (except Olympic lifters and weightlifters) full ROM because it’s not functional and injury risk is high. You can properly strengthen muscles with individually limited ROM (but you need to work on hips and ankles mobility for sure to improve ROM because it’s always a benefit). The only good thing is that you can develop muscles on better way and increase flexibility while doing full ROM – but better stop if you notice some technique issues.
PS: It makes sense that poor ankle dorsiflexion could also give you less powerfull vertical jump or sprinting. Less stretching (stretch shortening cycle) of powerfull Achilles tendon.
I mentioned that hams aren’t the cause of the “butt wink” because they cross both hips and knees (joints), but hip ADDUCTORS (m. adductor longus, m. adductor brevis, m. adductor magnus, m. gracilis and m. pectineus) could cause “butt wink” because they cross the hip joint only (in my opinion, it’s possible only if some adductors are pretty stiff/short for a number of reasons). Actually, the only one of these muscles crosses the hip joint and the knee joint – m. gracilis.
“When you go down into a squat or a sumo deadlift where your legs are out to the side, the main muscular limitation is the adductors, especially when you externally rotate your femurs. In the squat, the hamstrings are slacked because of the knee bend, but the adductors are not. They are the most likely muscular limitation around the hip to preventing good squat depth.” – Ryan DeBell.
Take a look at his phenomenal video below.
When it comes to the posterior chain exercises (deadlift, KB swing…) it’s always good to do them with minimalist (low heels anyway) shoes or barefoot because the full/better muscle activation (posterior chain muscles) is possible only on that way (plus better proprioception).
At the end, you should be avoiding “butt wink” positions especially when spine is under an external load (common back squat exercise for example) because your spine should be in “neutral” position to prevent injuries whatever you do. If you like executing exercises with full/almost full ROM do many alternatives where you unload your spine… plus by doing them in “sumo” positions you can decrease an injury risk even a bit more. When it comes to common back squat (which I personally don’t like because the load on spine is high) if you train for the sake of pure strength you can do fuller ROM but if you train for sports performance “quarter squat” is more specific option (of course, basic strengthening should start with fuller ROM – on that way you also work on necessary mobility a bit). Front squat is much more friendly option where you engage core more. Someone would say “yeah, but you engage quads more as well which can injury your knees.” I would say, “yeah, but you are doing squat, not deadlift… anyway, don’t be afraid of knee(s) injury – it’s not so dangerous 😉 …”
Thanks for reading and all the best,