It's not uncommon for cyclists to experience sciatica like symptoms because of a tight piriformis muscle that compresses the sciatic nerve. Especially so in the 17% of patients in which the sciatic nerve runs through the piriformis muscle. It's called, obviously, the
piriformis syndrome. The piriformis muscle's function is to turn the hip outward and to aid in the rotation of the foot. It's attached deep in the buttocks and goes to the lower back. It sits on top of the sciatic nerve in general and so if it's tight, it compresses the nerve and irritates it. And that (believe me) can be very painful.
I had this problem last year with almost debilitating pain that prevented me from riding and from cycling. No one could seem to figure it out so I bought a $40 iPad app that allows you to peel away the layers of muscle, tissue and nerves as you go down. I found the place where the pain was coming from and peeled away. My finger was smack dab on top of the piriformis muscle. I did the stretches, and immediately the pain ceased. Now, as I feel it tightening from overuse, I start stretching it.
Piriformis syndrome is relatively common in cycling but not so much in other sports. So if your MD or PT is unfamiliar with cycling in their sports medicine practice, they could easily miss this diagnosis.
There are a lot of good piriformis stretches if you google them. Find the ones that work best for you.
Literally, a magical solution to my problem. Serious problem for me that was gone in a matter of three days of stretching and largely in the first day.
J.