Purpose: To examine whether components of body composition (size, fat mass, and fat-free mass) were related to physical activity.
Methods: A random sample of 60 eligible sixth grade girls at each of 36 schools (six schools per region and six regions in total sample); complete measurements on 1553 girls. Physical activity was assessed over 6 d in each girl using an accelerometer, and body composition was assessed using a multiple regression equation using body mass index and triceps skinfold. Minutes of moderate-to-vigorous and vigorous physical activity were estimated from accelerometer counts per 30 s above threshold values determined from a previous study.
Results: Significant inverse relationships were found for all measures of body size and composition and all physical activity indices. The combination of fat and fat-free mass expressed as a weight and as an index (divided by height squared) along with race, SES, site, and school were most highly associated with physical activity in multiple regression analysis, accounting for 14-15% of the variance in physical activity. Fat mass was more closely related to moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA) than fat-free mass with higher standardized regression coefficients.
Conclusion: We conclude that both fat mass or fat mass index as well as fat-free mass or fat-free mass index make independent contributions in association with physical activity levels. These indices are recommended for future studies.
1Department of Physiology and Department of Nutritional Sciences, The University of Arizona, Tucson, AZ; 2Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC; 3Division of Epidemiology, University of Minnesota, Minneapolis, MN; 4Center for Human Nutrition, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD; 5Department of Human Performance and Health Promotion, University of New Orleans, New Orleans, LA; 6National Heart, Lung, and Blood Institute, Bethesda, MD; and 7Louisiana State University Health Sciences Center, New Orleans, LA
Address for correspondence: T. G. Lohman, Ph.D., Department of Physiology, The University of Arizona, 1713 E. University Blvd. #93, Tucson, Arizona 85721; E-mail: email@example.com.
Submitted for publication May 2005.
Accepted for publication December 2005.