Effects of function on rat femora

We evaluated the mechanical effects of different degrees of function and weight bearing on intact rat femora. Thirty rats were allocated to either an exercising, a nonweight-bearing, or a control group. The exercising rats were trained on a treadmill with a 6 weeks' running program of progressive intensity and duration. In the nonweight-bearing group, the left achilles tendon was severed at its insertion. The control rats were allowed normal activity. After 6 weeks, the animals were killed. The maximum bending moment and bending rigidity were increased in the exercised rats, whereas no differences were found between the control and nonweight-bearing rats. Bone weight and bone dimensions did not differ in the three groups. In the nonweight-bearing group, the maximum bending moment and bending rigidity were higher in the nonoperated on limb, as well as the outer and inner bone dimensions and the area moment of inertia. Our results indicate that exercise improves the mechanical characteristics of bone.