Exercise as an osteogenic stimulus

Abstract

The objective of the present study was to search for an effective exercise mode for strengthening the bones of young and pre- and perimenopausal healthy women in terms of bone mineral density (BMD), bone mineral content (BMC) and selected mechanical characteristics. Altogether 444 healthy women were involved in six experiments comprising two cross-sectional studies, two controlled trials and two randomized controlled trials. The subjects were female athletes and sedentary or physically active premenopausal young and perimenopausal middle-aged women. Information on living habits and health status was obtained with detailed questionnaires. BMD and BMC and bone dimensions were measured by dual energy X-ray absorptiometry. Maximum isometric strength, muscular and cardiorespiratory performance, and dynamic balance were assessed with standard methods. The training programs lasted 12-18 months and consisted of strength training, calisthenics, endurance training, and high-impact training. In the cross-sectional studies the squash players and weightlifters had significantly higher (7-19%) weight-adjusted BMD values than sedentary referents at all the measured sites except the femoral neck of the weight lifters. Unilateral training showed nonsignificant BMD and BMC changes. For the BMD of the femoral neck, the linear trend in the endurance group was significantly different (p=0.043) from that of the control group, the trend indicating a maintenace of the prestudy BMD level. The 18-month high-impact training resulted in significant increases in BMD at the loaded sites. These increases amounted to 1.4 - 3.7% in the training group in contrast to changes of 0-1.8% in the control group. The present results indicate that the important components of osteogenic exercise stimulus in premenopausal women are high strain rates and high peak forces in versatile movements. Furthermore, when the repetitive loading magnitude is low, the number of loading cycles is likely to increase in significance for improved bone characteristics.