THE EFFECT OF LONG-TERM EXERCISE ON VERTEBRAL AND FEMORAL BONE MASS, DIMENSIONS, AND STRENGTH - ASSESSED IN A RAT MODEL

The rat model has previously been used to test the effect of ovariectomy and of PTH administration on vertebral bone mass, size, and biomechanical competence. In this study, we used the same ''biomechanical rat model'' to assess the effect of long-term exercise on vertebral bone mass and quality and also on femoral bone mass, dimensions, and strength. Sixty female Fischer rats were randomized into four groups. Two groups were exercised for 5 days a week on a treadmill with a running distance of 2 km per day. The exercise program was initiated at the age of 2 months. The two exercise groups were investigated after 4 and 10 months. Two sedentary groups (observed for 4 and 10 months) served as controls. At death, three lumbar vertebral bodies (L4-L6) and the left femur were obtained from each rat, and changes in bone mass (ash density, trabecular bone volume [BV/TV]), bone size, and biomechanical competence were assessed. The results revealed an age-related (4-10 months) increase in vertebral bone mass and strength. The additional effect of exercise on the vertebral bodies was an increase in cross-sectional area and bone biomechanical competence. In the femoral bone specimens, an age-related increase in bone mass, size, and strength was also disclosed, and while exercise by itself had no significant influence on biomechanical parameters it did reduce cortical-endosteal bone resorption. The study has demonstrated an anabolic effect of a light exercise regimen on both femoral cortical bone and vertebral bodies (mainly trabecular bone). This anabolic effect was disclosed primarily during attainment of peak bone mass (6 months), but was also maintained during the consolidation phase (12 months).