Abstract / Summary
Abstract Physical activity declines during adolescence, but sex-specific patterns across pubertal stages remain incompletely understood. We analysed 21-day Fitbit data from 4,794 adolescents (47.8% female; median age, 12 years) in the Adolescent Brain Cognitive Development Study. Daily moderate-to-vigorous physical activity (MVPA), sedentary time and step count were examined across Pubertal Development Scale stages using sex-stratified multivariable linear regression. Females accumulated fewer steps (mean, 8,754 versus 10,431 steps/day) and less MVPA (22.4 versus 48.6 min/day) than males (both p < 0.001), whereas sedentary time did not differ by sex. With advancing puberty, sedentary time increased and step counts declined in both sexes. After covariate adjustment, sedentary time was higher from early puberty onward in males and from mid-puberty onward in females, whereas significant step-count reductions emerged at mid-puberty in males and at late puberty in females. MVPA was not associated with pubertal stage after adjustment. Mean MVPA remained below 60 min/day in every sex-stage group. These findings identify mid-to-late puberty as a potential window for sex-sensitive strategies to reduce sedentary time and preserve daily movement.