EFFECTS OF EXERCISE INVOLVING PREDOMINANTLY EITHER JOINT-REACTION OR GROUND-REACTION FORCES ON BONE-MINERAL DENSITY IN OLDER WOMEN

This study compared the effects of two exercise training programs, 11 months in duration, on bone mineral density (BMD) in older, sedentary women, Thirty-nine women, aged 60-74 years, were assigned to the follo wing groups: (a) a group that performed exercises that introduced stre ss to the skeleton through ground-reaction forces (GRF) (i.e., walking , jogging, stairs); (b) a group that performed exercises that introduc ed stress to the skeleton through joint-reaction forces (JRF) (i.e., w eight lifting, rowing); or (c) a no-exercise control group, BMD of the whole body, lumbar spine, proximal femur, and distal forearm was asse ssed five times at similar to 3-month intervals, The GRF and JRF exerc ise programs resulted in significant and similar increases in BMD of t he whole body (2.0 +/- 0.8% and 1.6 +/- 0.4%, respectively), lumbar sp ine (1.8 +/- 0.7% and 1.5 +/- 0.5%, respectively), and Ward's triangle region of the proximal femur (6.1 +/- 1.5% and 5.1 +/- 2.1%, respecti vely), There was a significant increase in BMD of the femoral neck onl y in response to the GRF exercise program (GRF, 3.5 +/- 0.8%; JRF, -0. 2 +/- 0.7%). There were no significant changes in BMD in control subje cts, Among all exercisers, there was a significant inverse (r = -0.52, p < 0.01) relationship between increases in whole body BMD and reduct ions in fat mass, suggesting a dose response effect of exercise on bon e mass, Although femoral neck BMD was responsive only to the GRF exerc ise program, some adaptations (i.e., increase in lean body mass and st rength) that were specific to the JRF exercise program may be importan t in preventing osteoporotic fractures by reducing the risk for falls. It remains to be determined whether all of these benefits can be gain ed through a training program that combines the different types of exe rcises employed in this study.