EFFECT OF RESISTANCE EXERCISE TRAINING ON CORTICAL AND CANCELLOUS BONE IN MATURE MALE RATS

The effect of resistance training on tibial cancellous and cortical bo ne was evaluated in rats by using static histomorphometry and Northern analysis. Five-month-old male Sprague-Dawley rats were randomly assig ned to exercise (Ex; n = 8) or control (Con; n = 4) groups. Animals we re operantly conditioned to press two levers, facilitating full extens ion and flexion of the hindlimbs (''squats''), while wearing an unweig hted vest. After an 8-wk familiarization period, Ex animals performed 3 sessions/wk for 17-19 sessions with progressively increased amounts of weight applied to the vest. Con rats completed the same exercise pr otocol without applied resistance. No difference in cross-sectional, m edullary, or cortical bone area was observed between Ex and Con rats i n the tibial diaphysis. In contrast, the cancellous bone area in the p roximal tibial metaphysis was significantly larger in trained rats. Tr abecular number, trabecular thickness, and the percentage of cancellou s bone covered by osteoid were significantly greater in the Ex animals compared with Con animals. In addition, steady state mRNA levels for osteocalcin for the Ex group were 456% those expressed in the Con grou p. The data demonstrate that resistance training increases cancellous bone area in sexually mature male rats and suggest that it does so, in part, by stimulating bone formation.