Maximal isometric strength and fiber type composition in power and endurance athletes.

The relationship between maximum isometric strength and muscle fiber type composition was examined in seven endurance and eight power trained athletes. Knee extension strength and ankle extension strength was assessed on 10 separate days and muscle biopsies were taken from the vastus lateralis and gastrocnemius muscles. The percent composition of slow twitch (ST) fibers and fast twitch (FT) fibers was determined from the biopsy samples. Correlation between maximal knee extension strength and percent ST fibers of the vastus lateralis was found to be 0.80 (n = 8,p less than 0.05) for the power group and 0.63 (n = 7,N.S.) for the endurance group. Corresponding correlation coefficients for the relationship between ankle extension strength and gastrocnemius percent ST fibers were -0.94 (p less than 0.01) and -0.19 (N.S.), respectively. The results suggest that the relationship to be expected between muscle fiber type composition and maximum isometric strength may well depend upon the muscle group under study as well as the type of athlete in terms of specific training adaptations.