According to Tom Seabourne “sprinters carry a huge amount of muscle in their quads and hamstrings. They are all muscle from sprinting.”
To a certain extent, this statement is true since sprinting does help develop the fast twitch fibers which can lead to greater muscle mass. However, increases in muscle mass typically occur from heavy weightlifting programs not from speed and explosive work. In other words, just because the explosive white twitch fibers are involved in sprinting, it doesn’t mean that they increase in size because of this.
Speed and explosive work often leads to the opposite — a decrease in muscle size! This becomes obvious if you have an athlete doing strength training for several months and then put him on to a speed and explosive type program. In addition, if you look carefully at many sprinters, you’ll see that they do not have very large calf muscles — the main muscles involved in the pushoff which are very explosive.
The quads may get more mass from the mainly eccentric and static work that they must do to keep the sprinter from “sinking” too much on the landing. To improve this action sprinting alone is not the most effective. It must be supplemented with strength training which most of the world’s best sprinters do.
If only sprinting were responsible for the increase in quad size, the sprinter would have to constantly keep increasing the speed of running. This would be great if it could be done. But once your speed is more or less developed, most of the running training is below maximum which is a further indication that sprinting will not increase the size of the muscles.
Also, keep in mind that running is a neuromuscular skill, not simply muscle development. Thus, doing exercises such as the squats, calf raises and true plyometrics will develop the muscles more as needed to help improve your sprinting speed. You’ll get much more development and greater speed in comparison to only doing more sprinting.
See Explosive Running for more information.