Quantifying Leisure Physical Activity and Its Relation to Bone Density and Strength


Medicine & Science in Sports & Exercise: December 2007 - Volume 39 - Issue 12 - pp 2189-2198
doi: 10.1249/mss.0b013e318155a7fe
BASIC SCIENCES: Original Investigations

Purpose: Compare three published methods of quantifying physical activity (total activity, peak strain, and bone-loading exposure (BLE) scores) and identify their associations with areal bone mineral density (aBMD), volumetric BMD (vBMD), and bone strength.

Methods: Postmenopausal women (N = 239; mean age: 53.8 yr) from Iowa (ISU) and California (UCD) completed the Paffenbarger Physical Activity Questionnaire, which was scored with each method. Dual energy x-ray absorptiometry assessed aBMD at the spine, hip, and femoral neck, and peripheral quantitative computed tomography (pQCT) measured vBMD and bone strength properties at the distal tibia and midshaft femur.

Results: UCD women had higher total activity scores and hours per week of leisure activity. All scoring methods were correlated with each other. No method was associated with aBMD. Peak strain score was negatively associated with polar moment of inertia and strength-strain index at the tibia, and total activity score was positively associated with cortical area and thickness at the femur. Separating by geographic site, the peak strain and hip BLE scores were negatively associated with pQCT measures at the tibia and femur among ISU subjects. Among UCD women, no method was significantly associated with any tibia measure, but total activity score was positively associated with measures at the femur (P < 0.05 for all associations).

Conclusion: Given the significantly greater hours per week of leisure activity done by UCD subjects, duration may be an important determinant of the effect physical activity has on bone. The positive association between leisure physical activity (assessed by the total activity score) and cortical bone measures in postmenopausal women may indicate a lifestyle factor that can help offset age-related bone loss.

1Nutrition Department, University of California, Davis, Davis, CA; 2Department of Food Science and Human Nutrition, Human Metabolic Unit, Iowa State University, Ames, IA; 3Bone Diagnostics, Inc., Fort Atkinson, WI; and 4U.S. Department of Agriculture, Agricultural Research Service, Western Human Nutrition Research Center, Davis, CA

Address for correspondence: Marta D. Van Loan, Ph.D., FACSM, 430 West Health Sciences Drive, University of California, Davis, Davis, CA 95616; E-mail: mvanloan@whnrc.usda.gov.

Submitted for publication November 2006.

Accepted for publication July 2007.

©2007The American College of Sports Medicine