Much focus in public health recommendations has been on achieving a sufficient amount of physical activity (of at least moderate intensity) for good health. For example, it is recommended that adolescents up to age 17 years should accumulate at least 60 min of moderate to vigorous activity daily, and that when possible adolescents with disabilities should meet these guidelines. However, it is now emerging in large population studies that the amount of sedentary behaviour, and not just the total amount of physical activity, is an important predictor of cardiovascular and metabolic risk. Sedentary behaviour can be defined as sitting and lying postures characterized by low energy expenditure. Increased sedentary time, especially the time spent in sedentary behaviour without a break, can have a negative effect on the metabolic and cardiovascular systems, independent of the amount of time spent exercising at moderate to vigorous intensity. Therefore, it is possible for a person who is sufficiently physically active according to guidelines, to be to be at risk of developing heart disease and diabetes if they spend prolonged periods sitting and lying.
It is also well recognized that people with cerebral palsy (CP) are a group that is particularly vulnerable to the negative health consequences of low levels of physical activity and increased amounts of sedentary behaviour. The physical impairments that characterize CP can result in a cycle of decreased physical activity, increased sedentary behaviour, and deteriorating muscle morphology leading to greater cardiovascular and metabolic risk and early mortality.
The study of Shkedy Rabani et al. confirms previous reports that physical activity levels of young people with CP are low compared with their typically developing peers. However, in addition to reporting physical activity levels, Shkedy Rabani et al. also report new and more detailed information about the sedentary behaviour of this population. Adolescents and young adults with CP are sedentary for between 82% and 96% of the day. These results are similar to sedentary behaviour reported for other populations with mobility disability, and indicate that young people with CP demonstrate substantially greater amounts of sedentary behaviour than people without health conditions. Of particular interest, Shkedy Rabani et al. reported other markers of sedentary behaviour such as the number of daily transitions from sit to stand, and the median duration of bouts of sedentary behaviour. As well as being sedentary for the majority of each day, these data suggests that adolescents and young adults with CP are sedentary for prolonged periods with few transitions or periods of light activity. Therefore, young people with CP may be at long-term risk of developing health problems not only because they are not physically active enough, but also because they spend too long in sedentary postures.
The issue is what to do about this problem. Attempts to increase levels of moderate to vigorous levels of physical activity in young people with CP have proven difficult to achieve and maintain, with only modest benefits found in a small number of trials. Another approach that is now being proposed for people with motor disabilities, and which may be applicable to people with CP, is to trial interventions that reduce sedentary behaviour. What is appealing about this approach is that these interventions are less intensive and so may be more achievable than interventions designed to increase moderate intensity physical activity. For example, designing and integrating standing work stations in classrooms, allocating time for students to walk or self-propel their wheelchairs between classes, and having limits on sustained screen time are practical strategies that could be trialled in future research. If strategies to reduce sedentary behaviour are going to be trialled, sedentary behaviour first needs to be measured. The study of Shkedy Rabani et al. is important because it is one of the first to measure and report detailed baseline information about sedentary behaviour in young people with CP.