I was a springboard diver in HS. Short, explosive motions. Never swam an event longer than 100 yds, where I did pretty well* (for a diver.) In short, I was totally twitch fibers. As I aged, I had to learn how to use more slow-twitch muscles and go more for endurance. My reflexes are no longer fast enough to do the diving, and swimming for its own sake sorta sucks. My musculature still isn't ideal for bicycling, and never will be; but I make do.