This one. Back in my Cat2 racing days, I developed tendinitis of the hamstrings. My sports doctor measured the strength in my quads and my hamstrings and the result was that they were woefully out of balance - overdeveloped quads and under developed hamstrings. It basically ended my racing career amongst othe things. Anyway, the doctor said at that time that it was a common problem with cyclists.

BTW, twenty years later, my hamstrings still flare up if I string together several weeks of 250 miles or more.