Reference Values for Physical Functional Performance Across Childhood, Adolescence, and Early Adulthood in Individuals with Intellectual Disabilities

Individuals with Intellectual Disabilities (ID) often exhibit reduced physical fitness, leading to early declines in the ability to perform daily activities. This study aimed to characterize and establish reference values for physical functional performance by sex and age group in school-aged children with ID. A total of 321 participants (ages 5–26 years) from special education schools were assessed. Physical functional performance was measured using the 4 × 10 m shuttle run (4 × 10 m), Timed Up and Go (TUG), Five-Repetition Sit-to-Stand Test (5R-STS), and Countermovement Jump (CMJ). Two-way ANOVA, Kruskal–Wallis tests, and percentile values (5th–95th) were calculated by sex and age group. Males consistently demonstrated higher performance than females. Cross-sectional comparisons showed higher 4 × 10 m, TUG, and 5R-STS performance during adolescence in both sexes, while CMJ performance was higher in males during early adulthood. Adolescents outperformed children in 4 × 10 m, TUG, and CMJ tests (p < 0.05). Females exhibited lower 4 × 10 m and CMJ performance in early adulthood compared with adolescence (p < 0.05), whereas males showed no significant differences across these stages. Physical functional performance in individuals with ID varied according to sex and age, with males generally demonstrating better performance. Adolescence is associated with higher performance, while females experience reductions in lower-limb power in early adulthood. These findings highlight sex- and age-related differences and support the need for targeted monitoring and intervention strategies in this population.