Objective assessment of sedentary time and physical activity throughout the week in adolescents with Down syndrome. The UP&DOWN study

• We described sedentariness and physical activity in adolescents with Down syndrome.
• There were no differences in time spent in both behaviours throughout the week.
• Males are more active than females during weekend days.
• Sedentary time increases and PA decreases with advancing age.
• It is important to decrease sedentariness and increase PA in this population.

This study aimed to examine the patterns of sedentary time and physical activity (PA) throughout the week in adolescents with Down syndrome (DS). The study comprised 109 adolescents with DS (68 males and 41 females) aged 11–20 years, participating in the UP&DOWN study, but only a total of 100 adolescents provided valid data. Sedentary time and total, light, moderate, vigorous, and moderate-to-vigorous PA (MVPA) were measured by accelerometers. There were no significant differences in the time spent in sedentary time and PA levels between weekdays vs. weekend days, as well as between school time vs. after school-time periods (all p > 0.05). Adolescent males engaged in more total PA, moderate PA, vigorous PA and MVPA than females on weekend days (all p < 0.05). Differences between age groups showed that sedentary time increases and PA decreases with advancing age in all analyses, so that the oldest groups were more sedentary and less active (all p < 0.05). Only 43% of adolescents with DS met the PA recommendations of ≥60 min/day of MVPA. Our findings show valuable information to be considered in future interventions aiming to decrease sedentary time and increase PA levels in adolescents with DS.