EFFECTS OF ENDURANCE EXERCISE ON BONE HISTOMORPHOMETRIC PARAMETERS ININTACT AND OVARIECTOMIZED RATS

Physical activity is important for maintenance of bone mass. The effec ts of exercise on bone histomorphometry were studied in 9-month-old in tact (INT) and ovariectomized (OVX) rats. The rats were either kept se dentary (SED) or were exercised (EX) on a treadmill at 21 m/min for 1 h/day 5 days/week for 3 months. Bone resorption as well as formation p arameters were significantly higher in OVX-SED than in INT-SED rats, i ndicating increased bone turnover in OVX rats. In OVX rats, lower oste oclast perimeter and number, lower labeled perimeter but higher minera l apposition rate (MAR) and bone formation rate (BFR) were associated with higher trabecular bone in OVX-EX compared with OVX-SED rats. In i ntact rats, trabecular bone mass and osteoclast number and perimeter w ere not affected by exercise. Labeled perimeter was slightly lower whi le MAR was higher and BFR was insignificantly higher in INT-EX than in INT-SED rats. Thus, exercise resulted in fewer resorption-formation s ites, as indicated by lower labeled perimeter, but higher activity of individual osteoblasts, as indicated by higher MAR, both in estrogen-d epleted and estrogen-replete states.