ARS | Publication request: Lower physical activity is associated with fat infiltration within skeletal muscle in young girls

Submitted to: Medicine and Science in Sports and Exercise
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 2011
Publication Date: June 20, 2012
Citation: Farr, J.N., Van Loan, M.D., Lohman, T.G., Going, S.B. 2012. Lower physical activity is associated with fat infiltration within skeletal muscle in young girls. Medicine and Science in Sports and Exercise. 44:7, 1375-1381.

Technical Abstract: Fat infiltration within skeletal muscle is strongly associated with obesity, type 2 diabetes mellitus, and metabolic syndrome. Lower physical activity may be a risk factor for greater fat infiltration within skeletal muscle, although whether lower physical activity is associated with fat infiltration in otherwise healthy youth is unclear. PURPOSE: We examined the relationship between physical activity and fat infiltration within skeletal muscle of the calf and thigh in girls. METHODS: This study was a cross-sectional analysis of the relationship between physical activity and fat infiltration within skeletal muscle in 464 healthy girls aged 8–13 years. Calf and thigh muscle density (mg/cm3), a measure of fat infiltration, was assessed at the 66% tibia and 20% femur sites relative to the respective distal growth plates of the non-dominant limb using peripheral quantitative computed tomography. Physical activity level was classified by past year physical activity questionnaire (PYPAQ) score. Correlations and multiple linear regression were used to assess relationships between physical activity and fat infiltration within skeletal muscle. RESULTS: Muscle densities of the calf and thigh were inversely correlated with percent total body fat (r = –0.37 to –0.48, all P values < 0.001) and total body fat mass (r = –0.33 to –0.40, all P values < 0.001). Multiple linear regression with physical activity, ethnicity, maturity offset, and muscle size as independent variables showed that physical activity was independently associated with muscle densities of the calf (P = 0.01) and thigh (P < 0.001). Thus, lower physical activity was associated with higher fat infiltration within skeletal muscle. CONCLUSION: A lower level of physical activity is associated with fat infiltration within skeletal muscle in healthy young girls. Longitudinal studies are needed to confirm these findings.