Background: Low levels of physical fitness are associated with low physical and mental health. The aims of this study were to assess the health-related physical fitness of children with intellectual disability (ID), and study the association of physical activity and motor development with physical fitness. Methods: One hundred and twenty-eight children with moderate to severe ID (83 boys; age 2–18 years) visiting specialised day programme centres engaged in field-based physical fitness tests (body composition, muscular strength, muscular endurance, and cardiorespiratory fitness). Scores were compared to reference values, and with linear regression analysis the association between the fitness outcomes and physical activity and motor development was studied. Results: High rates of overweight (23–25%) and obesity (10–15%) were found. A majority of the participants (71–91%) scored below reference values for muscular strength, endurance, and cardiorespiratory fitness tests. Physical activity and motor development were positively associated with scores on several fitness test (β = 0.27–0.44; p < 0.05). Conclusions: Children with moderate to severe ID visiting specialised day programme centres have strikingly low physical fitness levels. Policies and interventions to increase the physical fitness for this specific group of children are urgently needed, in which increasing physical activity and motor skills are expected to be effective components.

Background: Regular participation of children and adolescents with intellectual disabilites in physical activity is important to maintain good health and to acquire motor skills. The aim of this study was to investigate the habitual physical activity in these children.Methods: Sixty‐eight children and adolescents (2–18 years) with a moderate‐to‐severe intellectual disability were included in the analyses. They wore an accelerometer on eight consecutive days. Data was analysed by use of descriptive statistics and multiple linear regression analyses.Results: The participants took on average 6,677 ± 2,600 steps per day, with intensity of 1,040 ± 431 counts per minute. In total, 47% of the participants were meeting physical activity recommendations. Low motor development was associated with low physical activity.Conclusions: As more than half of the participants were not meeting the recommendations, family and caregivers of these children should focus on supporting and motivating them to explore and expand their physical activities.