Apparently if it gets really sore, it can turn into a syndrome and cause overall leg and lower back pain for runners. Glad I caught it before it turned into anything worse!
During the class, I noticed the stretches focusing on hip flexors (such as pigeon pose) definitely helped stretch this muscle out. I found this page which shows different stretches for the piriformis.
The great news is today the butt soreness feels great and is no longer nagging me. All I needed was to stretch it out and it is good. The bad news, however, is that the yoga class was so good (and I am admittedly out of studio practice), that I am more sore today than I have been for all of my marathon training. And the race is in 6 days!
I can only imagine that stretching everything out was a good idea and the soreness is showing I am much looser (I hope?). So this is definitely going to be an easy pre-marathon week. Anyone else ever get a nagging tinge in some unknown muscle? Do you run if you are sore from yoga or some other cross-training?