Effect of high-intensity running in rectus femoris muscle fiber in rats

The effect of a 12-week high-intensity intermittent exercise program on fib er type composition and the oxidative capacity of rectus femoris skeletal m uscle from 20 male Wistar rats (Trained, n=10; Sedentary, n=10) was histoch emically determined, The training exercise program was developed in a motor ized treadmill. It consisted of four running bouts of 2 min duration at 48 m/min, alternated with recovery intervals of 4 min. Training increased rela tive cross-sectional area of oxidative fibers (I, IIA, IIX) and decreased t he same parameter in type IIB non-oxidative fibers (P < 0.001). Our results suggest that this type of strength exercise program is enough to induce ch anges in muscle fiber composition. This opens a possibility to use this kin d of exercise in preventing and treating muscle atrophy. (C) 2001 Orthopaed ic Research Society. Published by Elsevier Science Ltd. All rights reserved .