Relationships between leg muscle fiber type distribution and leg exercise performance.

The object of the present experiments was to study the impact of muscle fiber type composition on "aerobic" and "anaerobic" performance capacities. Muscle fiber type composition was determined on biopsies from the m. vastus lateralis of 29 healthy males, consisting of sedentary subjects, physical education students, and short- and long-distance runners. The subjects performed: (a) a 30-s all-out ride on a cycle ergometer; b) a short-term (60 s), isokinetic, one-leg exercise test, (c) a 40-m sprint run; d) a 300 m run; and (e) a 2000-m run. Correlations between muscle fiber composition, expressed as % fast twitch (FT) fibers on one hand, and peak power, maximal peak torque, power decrease, and peak torque decrease in the laboratory tests were significant (P less than O.001) for the trained subjects but not for the sedentaries. Average speed during the 40-m sprint and the 2000-m run was positively (P less than 0.001) and negatively (P less than 0.001) related, respectively, to % FT in the trained subjects whereas no such correlations were present for sedentaries. It is suggested that fiber type composition in trained males is one factor contributing to ability to perform short-term as well as endurance exercise. This statement may not be true for the general population.