A weight-lifting exercise model for inducing hypertrophy in the hindlimb muscles of rats

A new method for strength-training of rat hindlimb muscles, comparable to human weight lifting, is compared with sprint training by a treadmill. The new training apparatus that can induce rats to perform human squats was designed. Squat training was composed of isotonic high-intensity, short-duration, and graded overload exercises. After 60 min of one bout of all-out squat and sprint training, serum creatine kinase activities were markedly increased in the squat group (P less than 0.001), but no significant changes were observed in the sprint group. These responses were reflected in the histological sections of the muscles. Some splitting and small fibers were observed only in the squat group, suggesting that different stimulations were applied to the muscles of both the squat and sprint groups. At the end of 12 wk of both types of training, performed 4-5 d.wk-1, the number of fibers in the plantaris muscles of the squat group was greater by 14% than that in the control and sprint groups (P less than 0.001), suggesting hyperplasia following hypertrophy. These results indicated that the muscle strength-training model presented here may provide a new insight into the muscle hypertrophy associated with hyperplasia induced by heavy resistance training.