Accelerometer-based 24-h movement behaviours in children and adolescents with Down syndrome

Children and adolescents with Down syndrome (DS) may show altered 24-h movement behaviours. This study compared physical activity, sedentary behaviour, sleep and rest-activity rhythms in paediatric DS with those of peers with normal weight and obesity. This cross-sectional study included 51 participants aged 8-18 years: 17 with DS, 17 with normal weight and 17 with obesity. Seven-day accelerometry assessed activity, sedentary behaviour, sleep and rest-activity rhythms. Group differences were analysed using adjusted ANCOVA, PERMANOVA and principal component analysis. Compared with normal-weight peers, participants with DS had significantly greater sedentary time and lower light, moderate and moderate-to-vigorous physical activity (all p < 0.001). They also exhibited longer sedentary bouts (p < 0.001), shorter physical-activity bouts (p = 0.037), a lower probability of transitioning from sedentary time to physical activity (p < 0.001) and a higher probability of transitioning back to sedentary time (p = 0.027). Rest-activity rhythms were less stable, with lower interdaily stability (p = 0.030), greater intradaily variability (p = 0.008), lower M5 activity (p < 0.001) and later M5 timing (p = 0.015) and cosinor acrotime (p < 0.001). Most activity and rhythmicity outcomes were similar in the DS and obesity groups. Participants with DS slept longer but had poorer sleep continuity. Overall 24-h behavioural profiles differed significantly among groups (p < 0.001).

Children and adolescents with DS display a sedentary, low-movement and less stable 24-h behavioural profile resembling that observed in obesity. Integrated assessment of activity, sedentary accumulation, sleep continuity and rhythmicity may support early identification of modifiable risk and guide individualized, family-centred interventions.

• Youth with Down syndrome are generally less active and more sedentary than typically developing peers and frequently experience disrupted sleep. • Objective studies integrating activity, sedentary accumulation, sleep and rest-activity rhythms across 24 h remain limited.

• Youth with Down syndrome showed a sedentary, low-movement, fragmented and less stable 24-h profile resembling that of peers with obesity. • Longer sleep did not indicate better sleep, as nocturnal wakefulness remained high and sleep efficiency was low.