Kettlebell S&S Hip bridge

[TimmyCK]

I'm curious about this move; usually when I see it demonstrated the knees are apart, with or without a band, emphasizing abduction. I remember the book saying that the reason was to prevent hyperextension of the back but I can't help but suspect there are other reasons it was selected - perhaps it inhibits the HFs? However, it seems to me that emphasizing adduction is the opposite of what you would want before lifting since we usually emphasize spreading the floor, activating the g. medius, not letting the knees cave in etc.
What are your thoughts on this? Why would one chose knees together or knees apart as a warmup/activation drill?

As a side note, I am aware of a study that found squeezing the knees to increase activation of the abs and glutes. Does it then become a tradeoff between adductor and glute/ab activation?
Source: (https://www.jstage.jst.go.jp/article/jpts/25/9/25_jpts-2013-117/_pdf)

 

[golubovalex]

My humble guess is that prying goblet squats are there to activate the right pattern of not letting knees cave in. On the other hand, bridges are aimed to stretch hip flexors which is possible only with the flat back. From that point of view, they are really good, at least for me.

 

[acutaiar12]

Having the shoe between my legs helps me focus on driving with my hips and not letting my lower back arch. The purpose is to open up the hips.

 

[BJJ Shawn]

Pavel explains the reasoning in the new BJJ course as well, as a way to prevent you from overarching your back and instead to extend your hips. I’m sure it has something to do with hip flexors, but he says it forces you to contract your glutes with the shoes and reduces strain on your lower back. Much like the S&S explanation, but in video form.

 

[Bauer]

Having the shoe between my legs helps me focus on driving with my hips and not letting my lower back arch. The purpose is to open up the hips.

Pavel talks about exactly this point on the BJJ fanatics video. The idea is to stretch the anterior chain (esp. hip flexors) and prevent excessive arching of the lower back. And also to activate the glutes, if this is an issue. Personally I prefer a wider stance and just pay attention to where I
I feel the stretch.

Edit: Forget to hit post and @BJJ Shawn beat me to it

 

[Lotto]

I practice a lot of yoga, a small extract from a reference I use to help make sure I am properly executing a pose is below and it pertains to "hip bridge" as SS refers:

It can be a challenge to get full hip extension in this pose. If the hamstrings and adductor magnus are not strong enough, the gluteus maximus may do too much and pull the legs into external rotation; or the other adductors will activate to bring the knees together but also flex the hips; or the rectus femoris will work to extend the knees, but won't fully extend the hips.
Spinal extensors, especially lumbar, may try to help, but too much lumbar extension is not helpful, because it will limit hip extension by putting tension on the psoas complex.
All in all, considering the many muscle actions that must be balanced for this pose to work, sustaining this basic posture actually requires a high degree of coordination.