+1 on Carbonfiberboy on the natural vs unnatural.

None of the motions our bodies are perfect, hence why there are so many (small) muscles to keep things right. "Natural" movements engage all of these, while isolated or "unnatural" do not, so they take things out of balance. Cycling and cyclic sports (pun intended=) ) sometimes disturb that balance as well, hence why we need to perform exercises focused on whole body strengthening, rather than just legs, etc. This is one of the reasons why rowers do chest exercises to balance the overdeveloped back muscles.