So first, the reasons why emphasising training glutes is really good:
- Can directly contribute to “stability” in the lower back via a structure called the thoracolumbar fascia
- The glutes are a strong posterior compressor of the pelvis, which can be useful for heavy squatting
However, where I think the “glutes is king” argument falls short is the fact that the glutes don’t have the best leverage from hip extension coming out of the hole.
The glutes have a very strong moment arm for hip hyperextension, or hip extension from “neutral” to back behind the body. In contrast, they have a relatively poor moment arm for hip extension from a flexed hip position, especially compared to the other large hip extensors. Considering that almost everyone these days has some degree of APT (and developing an APT is a fairly typical response to getting and bigger and stronger), very few people will have the ability to use glutes effectively in a squat.
Of these other large hip extensors, you’ve got the hamstring group and the adductor magnus. The hamstrings likely have a fairly minimal contribution to force production in the squat. This is because they must lengthen at the knee as they shorten at the hip during the concentric phase of a squat. As a result, hamstrings, at best, provide connectivity between the hip and the knee (this is part of something called Lombard’s paradox)
Finally, that leaves us with adductor magnus. Adductor magnus is the 2nd largest muscle in the body, and the strongest hip extensor from a flexed hip position. Additionally, a typically slightly wider-stance “powerlifting” squat, as opposed to a squat style you’d see Olympic lifters use, only serves to increase adductor magnus contribution. This has been verified with EMG, granted, EMG isn’t the end-all be-all.
At an even deeper level, certain movements must take place within the pelvis and pelvic floor to support the movement of very heavy loads. Specifically, the pelvis undergo a motion called counternutation, relative to the sacrum, and the pelvic floor must ascend. We know due to the anatomy trains concepts (fascial connectivity between muscles) that the adductor magnus is continuous with, and therefore contributes forces to, the pelvic floor. Additionally, counternutation of the pelvis is also an expression of the adduction of the hip (I.e. you can’t have one without the other). Therefore, adductor magnus wins again.
Glutes are great, especially for sprinters and jumpers, but for lifters they’re overrated. I think this mostly comes from a vast majority of research available about the biomechanics of the gluteals, and a relative sparsity of information about the adductor group