I'm sure it's not from an undeveloped quas muscle. It's in my dominant leg and I've been in the gym 1-2 per week since October. As far as weight trainin, my quads are the strongest they've ever been. I was in base 2 when the pain hit and I don't my hours more than 10-15% one week to the next. But the 3 days in a row of 3+ hour rides may have been a bit more than body could handle.