Weight-B~earing Exercise and Ground Reaction Forces: A 12-Molllth Randomized Controlled Trial of Effects on Bone Mineral Iʹensity in Healthy Postmenopausal Women

The effects of brier daily exercise on bone mineral density (BMD) were assessl~d in a randomized controlled trial in 44 healthy postmenop:ilusal women using weight-bearing exercise in a regimen adapted from osteogenic protocols reported in animal studies. UMD was assessed masked using dual energy X-ray absorptiometry at 0, 6, and 12 months. The sites assessed were the ]()roximal femur (neck, Wardʹs triangle, and trochanter) and the lateral spine (L2-3) to assess the etTects of the exercise, and the radius (ultradistal and 33% distal) as a marker for systemic etTects. The test group was required to perform 50 "heel drops" daily at home (raising the body weight onto the toes and then letting it drop to the Door keeping the lI.nees and hips extended) and to attend a weekly class of mixed exercises, which included some highimpact activity. The control group also attended a weekly exercise class run by the same teacher, which included only low-impact activity, and did Dexibility exercises at home daily. The ground lreaction forces (as a ratio of body weight) during heel drops were 2.5 to 3.0 NIN, with a rate of rise of 5~100 kN/sec. A )Iatient with an instrumented femoral implant allowed COmlJarison of compressive axial forces in the shaft of the proximal femur with the ground reaction forces, and these appeared to be transmitted undamped to the shaft of the femur. Initial analysis of BMD in the women showed no significant increases after 12 months of exercise at any site in either group, and the groups did not ditTer significantly from each other in this respect. Proximity to menopause was not associated with rapid bone loss, and in those who were more than 6 years postmenopausal, there was evidence for a maintenance etTect of the exercise in the test group. Compliance (83%) and increases in leg extensor power (15%) were similar in both groups, and when they were combined, BMD was maintained at the trochanter but feU significantly at the radius