Self-reported physical activity during leisure time was favourably associated with body composition in Norwegian adolescents.

Aim: We studied the cross-sectional association between self-reported physical activity and body composition in adolescents.

Methods: The Norwegian Fit Futures Cohort Study was conducted in the Tromsø and Balsfjord municipalities during 2010-2011. All 1,117 students in their first year of upper secondary high school were invited to attend an examination at the Clinical Research Unit at the University Hospital of Northern Norway and 93% agreed. After exclusions, we analysed 945 participants (51% boys) with a mean age of 16.1 years (range 15.5-17.5 years) with valid measurements. The associations between self-reported weekly hours of physical activity during leisure time and four measures of body composition were explored using linear regression.

Results: Self-reported physical activity was significantly associated with the fat mass index (p < 0.03) and lean mass index (p < 0.001) in both genders. The lean mass index increased with higher levels of activity and the fat mass index decreased. Physical activity was not associated with body mass index for either gender, but there was an inverse association with waist circumference in girls (p = 0.04).

Conclusion: Physical activity was favourably associated with body composition in Norwegian adolescents and showed contrasting associations with the fat mass and lean mass indexes.