Abstract
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.
Highlights
Prevention of osteoporosis, which is a risk factor for bone fractures, is an important component of sustained lifelong health
We previously found that the distance ran by rats that started Voluntary Wheel-Running (VWR) at five weeks of age peaked five weeks later and progressively declined until the end of the training period at 30 weeks later [14]
Values obtained for total and average distances ran by group 30VE are given for the 5-35, 5-15, and 16-35-week groups
Summary
Prevention of osteoporosis, which is a risk factor for bone fractures, is an important component of sustained lifelong health. Some forms of physical training during puberty can increase the mass of specific bones, which might help to prevent osteoporosis [12,13]. We previously found that the distance ran by rats that started Voluntary Wheel-Running (VWR) at five weeks of age peaked five weeks later and progressively declined until the end of the training period at 30 weeks later [14]. This phenomenon resembles the profiles of physical activity that are most commonly associated with the human transition from childhood to adulthood in modern society. Engstrom reported that the amount of time individuals spent on physical activity during leisure time at the age of 15 years was halved by the age of 20 years [15]
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