The Influence of Physical Activity on Bone Mineral Content in Women Over Eighteen Years of Age
The influence of physical activity on bone mineral content was investigated in 299 normally healthy, Caucasian women, aged 19 to 91 years. It was hypothesized that the more active women have a greater bone mineral content than their less active peers, and that body composition, skeletal size and calcium intake are important determinants of bone mass. Subjects were assigned to low, moderate or high activity level groups by five exercise scientists on the basis of a written questionnaire covering activities associated with the home, occupation, and recreational pursuits. Bone mineral content was measured by single photon absorptiometry at the midshaft and distal sites of the forearms. Anthropometric measurements, including skinfolds, circumferences and skeletal widths, were taken on each person. Densitometry was optional, chosen by 60% of the subjects. Dietary intake records were kept by a subgroup (n = 135) of the women. Significant differences in bone mineral content were found among all three physical activity groups, with the most active women having the highest, and the least active the lowest values. This was seen in areas of predominantly cortical and predominantly trabecular bone, as represented by the midshaft and distal forearm sites, respectively. The differences among activity levels remained significant when the factors of age and menstrual status were removed by the analyses of covariance. When the subjects were categorized by age (decades), differences among activity levels were found in all groups but the women in their forties. When subjects were divided into pre- and postmenopausal groups, only in the premenopausal women were differences due to activity level detected. No relationship between dietary calcium and bone mineral content was found. Activity level was associated with a leaner body, as the most active women had significantly smaller skinfold thicknesses and a lower percent fat than the moderately active women, who in turn were leaner than persons in the low activity group. These results show that a higher level of physical activity is associated with more bone mass and a leaner body for women of all ages, and that differences are apparent with moderate as well as high levels of activity.
Biology, Animal Physiology, Health Sciences, Public Health
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign