Journal of Osteoporosis and Physical Activity
Open Access

Abstract

Effects of Continuation of Modest Physical Activity after Vigorous Activity on Tibial Bone Mass in Adulthood in Wheel-Running Rats

Fumihiko Kariya, Jun Kitagawa and Keizoh Kobayashi

Objectives: We investigated whether different durations of voluntary exercise in rats during transition from the growing period to adulthood would have any positive effects on bone structure of tibiae in adult rats.

Methods: Male Sprague-Dawley rats (5 weeks old) were divided into six groups: (1) 10SC (n=6), sedentary controls housed in normal plastic cages until age 15 weeks; (2) 10VE (n=7), housed in a voluntary-exercise (running-wheel) device equipped with housing space until age 15 weeks; (3) 30SC (n=7), sedentary controls housed in normal plastic cages until age 35 weeks; (4) 30VE (n=7), housed in the voluntary-exercise device until 35 weeks; (5) 10C20E (n=7), housed in normal plastic cages until age 15 weeks, then in the voluntary-exercise device from age 16 weeks to 35 weeks; (6) 10E20C (n=10), housed in the voluntary-exercise device until age 15 weeks, then in normal plastic cages from 16 weeks to 35 weeks. At the end of the experimental period, the right tibia from each rat was taken for peripheral quantitative computed tomographic (pQCT) analysis.

Results: The results indicate 1) cortical area and bone mineral content (BMC) in the diaphyses were significantly greater in 30VE than in 30SC; 2) trabecular bone mineral density (BMD) in the proximal metaphyses was significantly greater in 30VE than in 30SC; 3) these positive alterations in tibial bone mass parameters in 30VE were not seen in 10VE, 10C20E, or 10E20C.

Conclusions: These results suggest that prolonging voluntary exercise after the growing period could be an important way of improving tibial bone mass in adult rats.