• Adolescence;
  • body fat;
  • fluctuation;
  • physical activity



The objective of the study was to test the hypothesis that greater fluctuations in physical activity lead to greater increases in body fat during adolescence.


Seven hundred fifty-six adolescents in Montreal, Canada, aged 12–13 years at baseline, completed a 7-d physical activity recall questionnaire every 3 months over 5 years. Body mass index (BMI), waist circumference, and triceps and subscapular skinfold thickness were measured at baseline and at the end of follow-up. Subject-specific linear regressions, expressing physical activity as a function of time, were fitted and physical activity fluctuation scores were obtained by averaging the absolute values of regression residuals. The association between body fat after 5 years and the physical activity fluctuation score was assessed in linear regressions adjusting for baseline body fat, average number of physical activity sessions per week, diet and sociodemographic variables.


Among boys, there were statistically significant positive associations between physical activity fluctuation and BMI (β, 95% confidence interval: 0.12, 0.02–0.21) and triceps skinfold (0.40, 0.17–0.63). The associations with waist circumference or subscapular skinfold were not statistically significant (0.22, −0.04–0.49; 0.13, −0.05–0.32, respectively). In girls, there were statistically significant negative associations between physical activity fluctuation and BMI (−0.12, −0.20 to −0.03), waist circumference (−0.54, −0.91 to −0.17), subscapular skinfold (−0.41, −0.56 to −0.26) and triceps skinfold (−0.22, −0.38 to −0.05).


Physical activity fluctuations appear to affect body fat during adolescence. Sex-specific interventions may be needed given that greater physical activity fluctuations seem unfavourable for boys and beneficial for girls.