EFFECTS OF PHYSICAL-TRAINING ON BONE ADAPTATION IN 3 ZONES OF THE RATTIBIA

This study has been conducted to examine the effects of physical exerc ise on the bone trabecular network and the cellular adaptations in thr ee different areas of a single bone, the tibia, Male Wistar rats (9 we eks old) were treadmill-trained for 0, 3, 4, or 5 weeks at 60% of thei r measured maximal O-2 consumption (VO2max). Histomorphometric analysi s of the proximal tibia of running and age-matched control groups was performed in the epiphyseal trabecular bone, in the primary spongiosa and in the secondary spongiosa, Dynamic and static bone cell activitie s and serum calcium and phosphorus levels were measured, VO2max increa sed significantly by 18.4% after 5 weeks of training, In the epiphysis , a 9% increase in bone volume, associated with more numerous trabecul ae (8%) was detected the third week of training, In primary spongiosa a significant increase (6.7%) in newly formed trabeculae was found, In secondary spongiosa bone volume increased significantly by 26.2% the fifth week of exercise and was associated with thicker trabeculae. The number of osteoclast profiles,vas significantly depressed, Osteoid su rfaces and bone formation rate increased significantly in weeks 3 to 5 , Serum calcium level were found to be significantly decreased in week s 3 and 4. There was no change in osteoid thickness or mineral apposit ion rate, These results suggest 1) a rapid increase in osteoblastic re cruitment without change of the cell activity in response to moderate exercise; 2) a decreased bone resorption associated with a marked incr ease in bone formation from the third week of training; 3) adaptation of the trabecular network to exercise that seems to be bone-site depen dent, suggesting a cell sensitivity to training-engendered strain dist ribution within the bone or to strain-related local factors.