Originally Posted by Jamie Crichton
Unless I'm very much mistaken, the piriformis is an external rotator of the hip. So why do we recommend flexing and externally rotating the hip as a stretch for the piriformis? I see this stretch everywhere, and while it is a nice feeling stretch which I do often myself, surely it can't be putting the piriformis in a stretched position?
Not quite sure, but it does seem to help a lot of people. I think it's mostly cause everything's tight in there so doing it will stretch a lot of things.
Stretching the LIMIT of external rotation and internal rotation are both good though. Much like you would do for a baseball pitcher with internal and external rotation to maintain mobility. Regardless, I'd say do both (internal and external of hip).
Internal rotation stretch (courtesy of I think one of Cressey's articles):
But yeah, it does seem hamstring in origin not piriformis like people have said. I'd work it all though: internal/external rotation and strengthening, Massage (tennis ball) everything in the hip, maybe some heat.