What muscles are involved in running the pipe?

Hi all, kind of a random question but I was thinking about it during wrestling. What muscles are involved in running the pipe off a single leg? There's a few dudes that are just strong as hell, even when they're not resisting, I have a lot of trouble bringing them down. They have tree trunk legs and the movement feels super weak to me.

I don't have an issue getting most people down but I want to know so I can maybe focus my S&C on developing the weaker muscles. Thanks yall!