Adaptations to endurance training at three intensities of exercise

This study was undertaken to investigate the influence of exercise intensity (running speed) on a number of alterations that are known to occur with exercise training. Rats were trained on three treadmill running schedules: 20 m/min, 27 m/min, and 35 m/min for 1 h/day. After 6 wk, lean body mass and body fat content were decreased to the same extent in all three trained groups. Thus, exercise appears to lower body fat by some mechanism that is not related to the amount of energy expended during exercise. Heart and adrenal gland weight-to-lean body mass ratios were increased by training. Heart weight-to-lean body mass ratio increased with increasing intensity of exercise but the adrenal weight-to-lean body mass ratio was independent of exercise intensity. Training increased muscle succinate dehydrogenase activity to the same extent in all three trained groups which suggests that the adaptation in respiratory capacity is not altered greatly by the intensity of training.