Measurement of physical activity in children and adolescents with cerebral palsy: the way forward

Participation in regular physical activity is recognized as a necessary contributor to health and well-being for children and adolescents with cerebral palsy (CP). Over recent years the number of papers on this topic has increased, attesting to the importance being afforded this issue. Despite this interest, research investigating the psychometric properties of measures of physical activity in individuals with CP has been relatively limited. This is of concern, as the underpinning of a good study design lies in the selection of measures which are known to be valid, reliable, and responsive to change in the population studied. Research in typically developing children supports the use of pedometers and accelerometers to accurately record physical activity. However, differences in gait biomechanics and energy expenditure means that specific validation is required for children and adolescents with CP. Systematic reviews on measurement of physical activity in individuals with CP have drawn limited conclusions other than to plead for additional high quality research. When the Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) criteria have been applied, studies investigating the validity of measures of physical activity ranged from Fair to Poor in quality, with little evidence to support the reliability of these measures in children with CP. Maher et al. answer this call, providing a robust evaluation of the NL-1000 pedometer (New Lifestyles Inc., Lee’s Summit, MO, USA). The authors have carefully considered their study design and reporting, enabling readers to interpret these results with confidence. Application of the COSMIN criteria to this paper rates the overall study quality as Excellent, with the exception of the description of missing data handling (which was Good). Rigorous statistical testing has been applied, sample size justified, and their findings carefully interpreted to highlight that the results apply to independently ambulant children, classified at Gross Motor Functional Classification System (GMFCS) levels I or II, and under controlled settings only. The accuracy of the NL-1000 in an individual classified at GMFCS level III, who walks with an external support and typically in a more crouched position, may be quite different and should be investigated separately. Future research that considers the measurement of physical activity in individuals across all GMFCS levels is required, but when doing so it is important to consider if step counts provide a relevant measure of physical activity for all. For an individual using primarily wheeled mobility, a step counting device is of limited use, given that the majority of physical activity performed would be missed by a pedometer. Accelerometers have an advantage in that they can be either wrist or waist mounted, meaning they are appropriate for children across all GMFCS levels, and most importantly provide data on activity intensity, which has been validated against energy expenditure in ambulant children and adolescents with CP. In addition, preliminary work in typically developing children suggests that pat-