ABSTRACTCOYLE, EDWARD F., DAVID L. COSTILL, and GEORGE R. LESMES. Leg extension power and muscle fiber composition.Med. Sci. Sports. Vol. 11, No. 1, pp. 12‐15, 1979. The purpose of this investigation was to relate muscle fiber composition to the isokinetic measure of peak torque production through a range of leg extension velocities. Twenty‐one males were biopsied from the vastus lateralis muscle to determine their percent distribution of slow twitch (% ST) and fast twitch (% FT) muscle fibers as identified through myofibrillar adenosine triphosphatase activity. All subjects showed a decline in peak torque with increasing velocities. Subjects with predominantly FT fibers were able to generate 11, 16, 23 and 47 percent greater relative peak torque than could predominantly ST subjects at lever arm velocities of 115, 200, 287 and 400 degrees/second respectively. Likewise the correlations between relative torque production and % FT were significant (p<.05) and increased from r=0.44 to r=0.75 as velocity increased from 115 to 400 degrees/second respectively. These data suggest that muscle fiber composition becomes increasingly more related to power performance as the velocity of movement increases.MUSCULAR POWER, MUSCULAR STRENGTH, MUSCLE FIBER COMPOSITION