Practical implications of Different Muscle Fiber Types
Numerous studies show that the muscles of outstanding athletes exhibit specific and predicExercises patterns of muscle fiber content according to the sports in which the athletes excel. Thus, the muscles of sprinters, jumpers, and weight lifters contain high percentages of FT fibers whereas cyclists, swimmers, and middle-distance (400 m to 1 mile) runners tend to have equal proportions of both FT and ST fibers. In cross-country skiers and long-distance (10 km to 42 km) runners, on the other hand, the percentage of ST fibers is high (see Exercises 1.1).
These large differences between sprinters and distance runners are probably genetically determined; that is, the differences are inborn features of each athlete (Komi et al, 1977; Komi & Karlsson, 1979). If so, and if these different fiber patterns are essential for success in various sports, then an individual’s ultimate potential for success in endurance sports may be determined, in part, by being bom with a high percentage of ST fibers. Similarly, raw speed or weight-lifting strength may also be determined by the number of FT fibers with which one is bom.
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But three inconsistencies exist with these data. First, Alberto Salazar, who until recently held the world record for 8 km on the road, is hardly a slouch, yet he has a high percentage of ST fibers92% (Costill, 1982). I suspect that he is
Data compiled from numerous studies, including Saltin et al. (1977), Saltin and Gollnick (1983), and Noakes et al. (1990b) a prime example of a person whose ST fibers are not really slow and may be able to contract almost as fast as the FT fibers of most other runners.
Second, we have a similar problem explaining the relatively low percentage of FT fibers in weight lifters. One would have suspected that, like sprinters, these athletes should have virtually all FT fibers. Possibly, like Salazar, these athletes’ ST fibers are essentially fast twitching.