Physical activity and bone density.

Habitual physical activity was assessed by questionnaire and interview as a part of the Tecumseh Health Study. There were 346 men, age 45-54, and 226 men, age 55-64 for whom such data were available. The 25 most active and 25 least active men in each group were selected as well as 25 farmers in each of the two age groups. Standard handwrist radiograms were available on the 50 farmers, 41 of the most active group and 40 of the least active group. From the x-rays, micrometrie measurements including length, medullary diameter and total diameter were made of the second metacarpal bone. Cortical area and percent cortical area were computed. Adjusting for age and height by analysis of co variance, the three groups were compared in the various bone measurements. There were no significant differences among the physical activity groups. As expected, bone density (percent cortical area) decreased with age. When the dominant hand was compared to the non-dominant hand, there was no significant difference in percent cortical area. Arm strength, grip strength and heart rate response to standard exercise were available on 36 of the men. When age, stature and weight were partialled out, there was no correlation between strength and percent cortical area. There was a slight tendency (significant at the 5% level) for the percent cortical area to be greater in more fit men (i.e. with lower heart rate during a standard exercise). Cortical bone decreases after about age 40 in men and women. The decrease is greater in women. The likelihood of bone fracture is linearly realted to the amount of mineral or bone lost (Hattner and McMillan, 1968). It is not surprising therefore that the incidence of hip fractures may increase as much as fifty fold from age 40 to age 70 (Chalmers, 1970). The evidence is convincing that extreme muscular inactivity results in demineralization of bone. However, the effects of less drastic changes in Supported in part by grants HE-14712 to University of Tennessee and HE 09814 to University of Michigan, both from the National Institutes of Health, U.S. Public Health