Already asked my physio about this, he had no idea. I've had piriformis issues and since they started, the hip on the right side (the same side as piriformis issues) has had very little internal rotation - maybe 5 degrees. This makes sense to me - the piriformis is contracted and tight (hence the pain), and it's an external rotator while hips are in neutral, so if it's tight and contracted it would limit my range of motion for internal rotation. But after I do short side planks on my right side (attempting perfect form and contracting glutes/abs hard while doing it) and breath into my diaphragm, suddenly my internal rotation on my right side is just as good as on my life side (40-45 degrees). So it seems like perhaps side planks somehow temporarily release the tightness/contraction in my piriformis? I feel like if I can figure out why this happens it might help me finally (more permanently) relax the piriformis so it can heal, but my physio is at a loss. I do lots of exercise that require my glutes to contract and none of them have this effect. I figured since it improved my hip flexibility you folks here might have some experience with this or ideas as to why it might happen. Any thoughts?