EFFECTS OF EXERCISE ON BONE-MINERAL DENSITY IN MATURE OSTEOPENIC RATS

Dual-energy X-ray absorptiometry (DXA) nas used to examine the effects of quantitative application of treadmill running exercise on bone min eral density (BMD) of the tibia and the fourth and fifth lumbar (L4 L5) vertebrae in mature osteopenic rats. Twenty 37-week-old rats with bone loss, resulting from feeding a relatively low calcium diet for 14 weeks after ovariectomy at the age of 23 weeks, were divided into fou r groups of five rats each according to the intensity and duration of the exercise: 12 m/minute, 1 h/day in group EX1; 18 m/minute, 1 h/day in group EX2; 12 m/minute, 2 h/day in group EX3; and sedentary control in group CON. With a standard calcium diet, the exercise was performe d 5 days a week for 12 weeks, and the BMD of both the right tibia and the L4 + L5 vertebrae was measured using DXA at weeks 0, 4, 8, and 12. At the end of 12 weeks of exercise, the right femur and the L5 verteb ra were dissected and the mechanical strength was measured using a thr ee-point bending test and a compression test, respectively. After 12 w eeks of exercise, a significant increase in the tibial BMD was observe d in only group EX1 compared with that in group CON (p = 0.0039, by tw o-way analysis of variance). However, any significant increase in the L4 + L5 vertebral BRID,vas not observed in any exercise groups compare d with that in the control group. While a maximum breaking force of th e femoral shaft in group EX1 was significantly greater than that in gr oup CON (p < 0.05, by Mann-Whitney's U-test), that in groups EX2 and E X3 did not significantly differ from that in group CON. However, there was no significant difference in a maximum breaking farce of the L5 v ertebral body among all the exercise and control groups. These results indicated that the beneficial effects of treadmill running exercise u nder a standard calcium diet were recognized only in the weight-bearin g bones of the mature osteopenic rats resulting from estrogen deficien cy and inadequate calcium intake only when an optimal level of exercis e was applied.