t is clear from Table 8.3 that considerable variation in the percentage of various fiber types exists even among successful athletes competing in the same event or sport. Indeed, although the percentage of type I (slow) muscle fibers is highly correlated with an individual’s V̇O2 max, the percentage of type I fibers can explain only 40% of the variation in V̇O2 max between individuals (68). Furthermore, two equally successful 10,000-m runners have been shown to differ in the percentage of slow fibers that each possesses. For example, one runner might be found to possess 70% slow fibers, whereas a similarly successful runner can possess 85% slow fibers. This observation demonstrates that an individual’s muscle fiber composition is not the only variable that determines success in athletic events (22). In fact, success in athletic performance is due to a complex interaction of psychological, biochemical, neurological, cardiopulmonary, and biomechanical factors (14).