DETRAINING EFFECTS ON BONE MASS IN YOUNG MALE RATS

The effects of exercise training and detraining on bone mass were asse ssed in young male Wistar rats. The rats were divided randomly into se dentary control (C) and exercise training (T) groups. The T rats were trained for 10 weeks followed by a 10-week detraining period. Training consisted of running exercise on a rodent treadmill at 35 m/min, + 5- degree inclination, 60 min/day, 5 days/week. Training induced signific ant gain in fat-free dry weight and length of bones (femur, tibia, hum erus and coxa) and bone mineral content (femur, tibia and humerus). Hi stological analysis at the tibial mid-shaft revealed a significant inc rease in total and cortical areas without a significant change in marr ow area in the T group. Bone mass acquired through running exercise wa s retained for 10 weeks after cessation of training. These results ind icate that running exercise leads to increased cortical bone associate d with enhanced periosteal bone formation which is also maintained eve n after stopping exercise training, and suggest that training effects on the skeleton in bone mass level do not diminish immediately after c essation of training.