Comparison Of Calculated Estimates And Muscle Biopsy Of Fiber Type Distribution In Master Athletes

Abstract

Muscle fiber type distribution may be an important factor in determining physical performance in master athletes. Muscle biopsy is an invasive procedure to determine fiber type distribution and presents many difficulties. Therefore, a non-invasive method using isokinetic dynamometry to estimate fiber type distribution would be advantageous. PURPOSE: To establish a relationship between calculated estimates of Type II muscle fiber proportions and the percentage of Type II fibers determined from muscle biopsies of the vastus lateralis (VL) in master athletes. METHODS: The participants included 12 master athletes (53.5±12.6 years; 70.9±11.3 kg), including 3 women and 9 men. Isokinetic dynamometery (Kin-Com 500H) was used to assess peak torque and power output at 180°/sec as well as a fatigue test which consisted of 50 consecutive contractions at 180°/sec to establish fatigue resistance of the knee extensors. Fat-free thigh mass was determined by dual-energy X-ray absorptiometry (Hologic QDR 1500). Muscle biopsies were taken of the VL on a separate day from the isokinetic testing to determine percentage of Type II fibers. Linear regression analysis was used to estimate the proportion of Type II fibers. RESULTS: The regression model included the following variables: T50 = relative torque after 50 contractions in the fatigue test; P180 = power at an angular velocity of 180°/s; FFTM= fat free thigh mass. Regression estimates of proportion of Type II fibers were not significant at the p<0.05 level (R = 0.377, R2 = 0.142, SEE = 15.21). CONCLUSION: Isokinetic dynamometry is not a valid tool for estimating muscle fiber type composition in Master athletes.