TRAINING INCREASES THE IN-VIVO FRACTURE STRENGTH IN OSTEOPOROTIC BONE- PROTECTION BY MUSCLE-CONTRACTION EXAMINED IN RAT TIBIAE

The effect of high-intensity training on the in vivo lower leg fractur e strength during muscle contraction was investigated in osteoporotic rats. 20 Wistar rats were ovariectomized and given a low calcium (0.01 %) diet. 7 weeks after ovariectomy they were randomized into training (T) and sedentary (S). The S group was kept cage-confined without any intervention. The T group ran on a treadmill with 10 degrees inclinati on 5/7 days for 8 weeks. A maximum intensity of 27 m/min was reached a fter 4 weeks. After 8 weeks, the right lower legs of the anesthetized animals were loaded in three-point ventral bending until fracture occu rred during electrically-induced muscle contraction. The left tibiae w ere excised and fractured at the same level as the right tibiae. Weigh t gain was equal in the two groups. Energy absorption and deflection a t fracture were significantly higher in the T group than in the S grou p in vivo during muscle contraction. In vitro, there were no significa nt differences in mechanical results. The mediolateral outer diameter was larger in the T group, and the maximal stress that the tibia could withstand was lower than in the S group. We conclude that 8 weeks of high-intensity training of osteoporotic rats increased the structural lower leg strength during muscle contraction. The reduced maximal stre ss in the training animals indicates a reduction in bone material qual ity. The increase of in vivo structural strength must reflect an incre ased protective effect of muscle contraction due to training.