Quantifying leisure physical activity and its relation to bone density and strength.
OBJECTIVE
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).


CONCLUSIONS
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.
Shedd
Kristine M
KM
Nutrition Department, University of California, Davis, CA 95616, USA.
Hanson
Kathy B
KB
Alekel
D Lee
DL
Schiferl
Daniel J
DJ
Hanson
Laura N
LN
Van Loan
Marta D
MD
D015519:Bone Density / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007899:Leisure Activities; D008875:Middle Aged; D008954:Models, Biological; D010024:Osteoporosis / Q000453:epidemiology*; D005082:Physical Exertion / Q000502:physiology*; D017698:Postmenopause / Q000502:physiology; D011795:Surveys and Questionnaires