Evidence for measurement properties of the 6MWT varies largely among chronic pediatric conditions. Further research is needed in all patient groups to explore the ability of the 6MWT to measure significant and clinically important changes. Until then, changes measured with the 6MWT should be interpreted with caution. Future studies or consensus regarding modified test procedures in the pediatric population is recommended.

. The studies were identified by two independent researchers following predetermined inclusion and exclusion criteria. The methodological quality was determined using the McMaster University critical review forms for qualitative or quantitative research and was numerically rated according to the criteria developed by Imms. RESULTSThe initial electronic search yielded 10 161 articles, of which six were qualitative and 12 were quantitative studies. These studies showed that a diverse range of positive and negative factors were associated with participation in physical activity, such as self-efficacy, physical fitness, increasing age, and the availability of equipment and local facilities.INTERPRETATION Future intervention studies could use these results, within the context of an individual child and his or her environment, as the basis for increasing physical activity levels, starting in early childhood and continuing throughout adolescence and into adulthood. An increased awareness of and focus on providing appropriate equipment and adapted sports in the child's own environment by policy makers might increase physical activity levels.A recent Lancet series 1 reported on the importance of being physically active in reducing the development and mortality of non-communicable diseases such as cancer, type II diabetes, and cardiovascular disease.2 For children in particular, the benefits of physical activity have been consistently documented and it is recognized that encouraging a physically active lifestyle from an early age is important. 3Physical activity can increase the physical, emotional, and social well-being of children with physical disabilities, as well as increasing their functional independence, integration, and quality of life and positively impacting their future health.4-6 Therefore, it is alarming to see a decline in the physical activity of young people. 7 Children with physical disabilities are even less physically active than their peers with typical development.8-11 A systematic review recently showed that young people with cerebral palsy (CP) participated in habitual physical activity at a rate that was 13% to 53% lower than in those with typical development and 30% lower than the recommended guidelines.12 A group of 85 Dutch children with several physical disabilities had significantly lower physical activity, with a prevalence of overweight and obesity three and six times higher respectively, than children with typical development. 13 Moreover, a large group of children with disabilities participating in a Fitkids exercise therapy programme showed both reduced aerobic fitness and a high prevalence of overweight and obesity before the programme. 14 Another systematic review identified a range of personal, social, environmental, and policy-and programme-related factors that influence physical activity in children and adolescents with disabilities. 15 The available literature includes several types of disabilities, including both intellectual and behavioural disabilities, which makes it difficult ...