Effect of treadmill exercise on tibial cortical bone in aged female rats: a histomorphometry and dual energy x-ray...

The aim of this study was to increase our understanding of the effect of exercise on cortical bone mass and turnover in aged female rats. Female Sprague-Dawley rats, 14 months of age, were divided into four groups: 8 controls and 10 exercised for the 9-week study, and 8 controls and 9 exercised for the 16-week study. Exercise consisted of treadmill running at 17 m/min for one h/day and 5 days/week for 9 and 16 weeks. All animals received double fluorochrome labeling of bone prior to sacrifice. Histomorphometric analysis was performed on 30-microns-thick Villanueva-stained, undecalcified cross-sections of the tibial shaft. Tibial diaphyseal mineral density of each rat in the 16-week study was measured by dual energy x-ray absorptiometry in vivo at 0, 9, and 16 weeks. The diaphyseal mineral density of the exercised group was significantly greater than that of the control group (p < 0.05 by two-way ANOVA) and the individual slopes of the density vs. time was found to be higher in the exercised than in the control animals (mean +/- SE of exercised 0.56 +/- 0.13 vs. control 0.19 +/- 0.07 mg/cm2/week, p < 0.05) by the end of the experiment. The results of the histomorphometric analysis after 9 weeks of exercise showed that the periosteal labeled surface, mineral apposition rate, and bone formation rate were profoundly increased by 192% (p < 0.001), 35%, and 206% (p < 0.01), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)