We observed the effects of sodium bicarbonate supplement on bone mass in rats on strenuous treadmill training. Sixty female Wistar rats (93-days-old; mean initial weight 261 +/- 16 g) were studied. One group of 15 rats was killed at the beginning of the experiments (basal control group), while another group of 15 rats was not manipulated (Exer-NaB-). Another group of 15 rats was exercised but did not receive sodium bicarbonate (Exer+NaB-), while the final group of 15 rats exercised and received sodium bicarbonate (Exer+NaB+) at a dose of 0.05 mg/kg/day, administered by esophageal catheter on exercise days. These rats were killed at the end of 11 weeks. Femoral and vertebral length, weight, and bone mineral content (BMC) and density (BMD) were measured. According to ANOVA with the Tukey-Kramer test, femur length and weight, vertebral weight, femur BMC and BMD, vertebral BMC and BMD and the ratio between femur and vertebral BMC and final body weight, and plasma bicarbonate were lower in the basal control and Exer+NaB- groups than in the two other groups (P < 0.005-0.0001). Overall, there was a positive correlation between femur and vertebral BMC and femur BMC and length (P < 0.0001 for all). Only in the Exer+NaB- group was there a positive association between plasma bicarbonate levels and femur length (r = 0.78; P < 0.0005). Our study demonstrates the adverse effects of strenuous exercise on bone, and the usefulness of sodium bicarbonate supplements in preventing and minimized these effects.