Chapter 41.1, Problem 1CSC

The legs of champion sprinters like Usain Sort have about 80% fast-twitch fibers capable of the rapid, explosive contractions that are so essential to blasting off the starling blocks. The legs of world-class marathoners like Dennis Kimetto. on the other hand, have about 80% slow-t witch fibers, which are less explosive but can rapidly contract again and again, each leg stepping about 11.000 times to complete a marathon. Both athletes probably have roughly the same number of muscle fibers in their legs, but Bolt's muscles are larger because he has mostly thick, fast-twitch fibers, while Kimettos muscles have a predominance of thin, slow-twitch fibers. Are there likely to be differences in Bolt's and Kimetto’s tendons and bones as well? You'll find out in Section 41.3.