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 ovariecto my and of PTH administration on vertebral bone mass, size, and biomech anical 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 streng th. Sixty female Fischer rats were randomized into four groups. Two gr oups were exercised for 5 days a week on a treadmill with a running di stance 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 dens ity, trabecular bone volume [BV/TV]), bone size, and biomechanical com petence were assessed. The results revealed an age-related (4-10 month s) increase in vertebral bone mass and strength. The additional effect of exercise on the vertebral bodies was an increase in cross-sectiona l area and bone biomechanical competence. In the femoral bone specimen s, an age-related increase in bone mass, size, and strength was also d isclosed, and while exercise by itself had no significant influence on biomechanical parameters it did reduce cortical-endosteal bone resorp tion. The study has demonstrated an anabolic effect of a light exercis e regimen on both femoral cortical bone and vertebral bodies (mainly t rabecular bone). This anabolic effect was disclosed primarily during a ttainment of peak bone mass (6 months), but was also maintained during the consolidation phase (12 months).