Histomorphometry of long bone growth plate in swimming rats.

In exercises involving running, muscle power and gravitational forces act together to affect bone mass in accordance with Wolff's law. However, the direct effect of muscle activity on bones in non-weight-bearing activities, such as swimming, has not been explored. Previous data indicate that swimming exerts a positive effect on bone growth and development in young rats. We performed a histomorphometric study on the effect of swimming on the growth plate and subepiphyseal area of young adult rats. The experiments were carried out on 28 12-week-old albino Sabra rats. One group of 14 rats was trained to swim 1 hour/day, 5 days a week, for 12 weeks. Another group of 14 rats served as controls. The proximal femur and humerus of each animal were examined histomorphometrically. There was an increase in the subepiphyseal cancellous bone trabecullae of the femur. In the growth plate there was an increase in the number of column cells and proliferative cells. These changes were more pronounced in the femur than the humerus. We conclude that swimming induces an increase in subepiphyseal cancellous bone in young adult rats by enhancing growth plate activity.