A while back I read an article by a young strength coach, Nick Tumminilo about how the typical figure four piriformis stretching is actually stretching more of the posterior lateral hip capsule and may lead to problems such as hip impingement. I also just listened to Nick on a strengthcoach.com podacst talking about the same subject. Nick is a smart young man and you know what? He is right.
In the supine piriformis stretch and the standing leg cradle the hip is flexed above 90 degrees, externally rotated and abducted. This is actually putting the piriformis in shortened position, not a stretched position.
"The supine piriformis stretch is not an effective stretch for the piriformis"
"You can see the hip is obviously abducted during the leg cradle"
"In the neutral hip position the force vectors of piriformis action contribute to hip abduction, extension and lateral (external) rotation. It might be assumed that the hip must flex, adduct and medially rotate to stretch piriformis, but this isn't the case. As the hip flexes, the rotation moment of piriformis changes such that by full hip flexion it becomes a medial (internal) rotator." (Travell & Simons, 1992)
"The transition point for this change in action is considered to occur at about 60 degrees of hip flexion." (Kapandji 1970, Lee 1989)
In the article, Tumminilo states that "In order to effectively stretch the piriformis as an internal rotator (above 60 degrees of hip flexion) we need to place the hip into flexion, external rotation and adduction. You will see this occur in the protocol below."
So here is the strategy that Nick is using. I have been using it and I like it a lot.