Physical Activity and Bone Mass
Summary

Hamilton CJ, Thomas SG, Jamal SA. Associations between leisure physical activity participation and cortical bone mass and geometry at the radius and tibia in a Canadian cohort of postmenopausal women. Bone 2009 Nov 5. [Epub ahead of print]. Level of evidence: II-2.

The purpose of this study of a Canadian cohort of healthy postmenopausal women (n = 234; mean age, 62) was to determine associations between leisure physical activity participation and bone mass, and geometry at the radius and tibia using peripheral quantitative computed tomography (pQCT). Leisure physical activity participation was assessed using the Minnesota Leisure Time Physical Activity Questionnaire to generate a total activity score (mean, 105; range, 0-840). Researchers used pQCT to measure bone mass and geometry at the distal and midshaft sites of the nondominant radius and tibia.

Total activity score was positively and significantly associated with total content, total area, cortical content, and cortical area at the midshaft sites of the radius and tibia, as well as bone bending and torsional strength parameters at the midshaft radius and tibia (P < 0.05 for all associations). No associations were observed between total activity score and trabecular bone parameters. Leisure physical activity participation was positively associated with bending and torsional strength at weight-bearing and non-weight-bearing bone sites, as well as cortical bone mass and geometry. In postmenopausal women, leisure physical activity may have the potential to modify bone strength and influence bone fragility.

Commentary by David L. Kendler, MD

This interesting study reports bone peripheral pQCT data at the radius and tibia of active Canadian women. As it is observational, the reported associations between bone structural parameters and calculated strength indices are not necessarily reflective of the effects of exercise. These data will, however, be useful in designing appropriate randomized controlled clinical trials on the effects of activity on cortical and trabecular bone. In addition, the small changes noted and the large coefficient of variation make such measurements of no utility in individual patients.

The authors have found small but statistically significant associations between physical activity and bone strength, with the effects being on cortical bone. In interpreting the results of this trial to our patients, we should certainly encourage exercise and can suspect that this will improve cortical bone strength. The amount of exercise optimal for this effect and the effects of this improvement on fracture prevention remain the topics of future clinical trials.

From the NAMS First to Know e-newsletter released January 26, 2010

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