Abstract
Physical activity is important for young people's health. The emphasis over the last 2 decades has been on moderate to vigorous exercise when designing activity and exercise programs for children and adolescents with cerebral palsy (CP). Emerging evidence suggests that sedentary behavior is distinctly different from a lack of moderate to vigorous physical activity and has independent and different physiological mechanisms. The concept of concurrently increasing moderate to vigorous physical activity and replacing sedentary behavior with light physical activity may be beneficial for children and adolescents with CP. This article is a summary of the evidence for what works and what does not work for improving the physical activity of children and adolescents with CP. It also discusses what is known about sedentary behavior of children and adolescents with CP and what research directions are needed to build foundational knowledge in this area with this population.
Cardiorespiratory fitness and muscle strength are considered the major components of health-related fitness.1,2 In the general population, a low cardiorespiratory fitness level is associated with shorter life expectancy and a higher risk of developing type II diabetes, cardiovascular disease, and some types of cancer.3,4 Strategies to increase physical activity levels in children and adolescents with cerebral palsy (CP) are considered important for long-term health.5 Exercise programs for children with various disabilities, therefore, have become a contemporary focus of intervention, especially for school-aged children and adolescents.6–13 Frequently used physical activity guidelines for children and adolescents recommend daily physical activity for 3 or more sessions per week that last at least 30 minutes and promote moderate to vigorous levels of exertion.14,15
Recent research suggests that there are specific metabolic health consequences arising from “nonexercise” time or sedentary behavior, even in individuals who meet the minimal public health recommendation of 30 minutes of vigorous activity per day.16 Interest in decreasing sedentary behavior in the general population has exploded in the last decade,17–19 receiving widespread media attention. Different health benefits and physiological mechanisms are associated with exercise programs designed to increase moderate to vigorous physical activity for short periods (fitness programs) compared with health strategies designed to decrease long periods of sedentary behavior by introducing light-intensity activities.20–22 The health risks of being an “active couch potato” (highly active for relative short periods and sedentary the rest of the day) are becoming better understood and are associated with an increased risk of type II diabetes and cardiovascular disease, which lead to premature mortality.19
Cerebral palsy is the most common childhood neurodevelopmental disorder associated with lifelong motor impairment.23 The early years of rehabilitation focus on optimizing physical potential until gross motor ceiling capacity is reached at around 5 years of age.24 The aim of rehabilitation shifts during the childhood and adolescent years to place a greater emphasis on necessary compensations and environmental accommodations to optimize independence, participation in daily life, and prevention of secondary impairments.25 Throughout the life span of individuals with CP, movement restrictions alter energy demands, metabolic rate, perceived exertion, walking speed, stride length, and stepping frequency (in children who are ambulatory)26–28—all of which contribute to poor fitness.29–31
For children and youth with CP, physical activity interventions have focused on increasing participation in moderate to vigorous levels of intensity of physical activity. Intervention recommendations must now be broadened to include addressing the deleterious effects of sedentary behavior, regardless of whether the person with CP meets the minimal daily exercise guidelines. The new behavior strategy of decreasing sedentary behavior represents an innovative approach to exercise and health for children with CP. It is an appealing concept because it does not involve short bursts of intense exercise at activity levels that may be challenging for children with CP to achieve. Considering the burgeoning interest in the science of sedentary behavior, it is timely to revisit the evidence related to physical activity and sedentary behavior and its application to the health of children and adolescents with CP. This perspective article aims to: (1) review the assumptions regarding the importance of fitness for children with CP, (2) appraise the evidence for what works and what does not work for improving the fitness of children and adolescents with CP, (3) discuss what we know about sedentary behavior of children and adolescents with CP, and (4) identify gaps in the current research base and propose solutions to addressing these gaps.
Fitness and Children With CP
Cardiorespiratory fitness and muscle strength are considered the major components of health-related fitness because of their strong relationship with improved health.1 Children with CP usually have poor physical fitness.32–34 Cardiorespiratory fitness and muscle strength are usually both affected29–31 due to both primary impairments (eg, muscle biology and strength) and the resulting secondary impairments (eg, contractures and movement limitations). In the general population, low health-related fitness levels are associated with a decreased life expectancy and a higher likelihood of developing type II diabetes, obesity, and some forms of cancer.3,4 These long-term effects of poor cardiorespiratory fitness and decreased muscle strength have not been studied in adults with CP, but we can assume, from our knowledge of the general population, that lack of physical activity sets up a pattern of disuse that leads to further impairment and deconditioning. Deconditioning triggers a spiraling down into further inactivity that increases the potential for increased levels of disability and may contribute to further mobility restrictions. These factors underpin the rationale for increasing the fitness levels of children and adolescents with CP.35–37
What Works and What Does Not for Improving the Fitness of Children and Adolescents With CP?
What do we know about the effectiveness of moderate to vigorous training programs (cardiorespiratory training and muscle strengthening) in relation to physiological measures and functional abilities for children and adolescents with CP?
Cardiorespiratory Training
Two systematic reviews investigated the effect of cardiorespiratory training for children with CP38,39 and concluded that training may improve the physiological parameters associated with aerobic fitness. As a result of early studies, training programs to increase the aerobic fitness of children and adolescents with CP became popular.6–10 However, 2 reviews34,35 included studies that were not randomized trials, and thus the level of evidence from which these recommendations were made was low and the effects were likely overestimated. In the most recent systematic review based solely upon randomized controlled trial (RCT) data, the authors concluded that there was limited evidence to support the assumption that children and adolescents who participated in a cardiorespiratory training program demonstrated short-term improvements in aerobic fitness.40 This review provided no information about long-term effects. The results of 2 published RCTs that aimed to improve cardiorespiratory fitness and included a follow-up measurement after the intervention suggest that the increased aerobic capacity obtained directly after the intervention was short-lived and not maintained at 3- and 4-month follow-ups.6,7
The activities the children performed in the RCTs included in this review varied from uphill walking8 and functionally based walking and running exercises7 to cycling, running, wheelchair driving, training on a balance board, swimming, and mat exercises.6 The training intensities varied from 60% to 80% of the maximum heart rate. This range of heart rates corresponds to the suggested training intensity of 64% to 95% of the maximum heart rate the American College of Sports Medicine has labeled as moderate to vigorous training.41
Muscle Strengthening
Muscle strengthening has become a very popular rehabilitation intervention for children and youth with CP, especially as no adverse effects are evident.42,43 Recently, conflicting views regarding the interpretation of the efficacy of the strength training evidence have been published.35,37,44 The current evidence from RCTs focusing on resistance training of the lower extremities in children and adolescents with CP appears insufficient to either support or refute the efficacy of increasing muscle strength in children with CP.35,37 In the RCTs that included follow-up measurements, the results suggest that gains from muscle strengthening are not maintained after training is discontinued.45,46
In conclusion, there is some evidence that cardiorespiratory or muscle strengthening fitness regimens for children and adolescents with CP result in very short-term improvements,35,37,38,40 but there is no evidence to support the assumption that the benefits will continue over the long-term without regular exercise opportunities. The literature suggests that if the general health of children with CP is to be improved by aerobic fitness and muscle strengthening intervention programs, it is essential that training continues on a regular basis to ensure that the fitness benefits are maintained. Just as in the general population, children and youth with CP face the “use it or lose it” dilemma of conditioning.
What does this dilemma mean for clinicians? Exercise training aimed toward increasing the aerobic fitness, muscle strength, and general health of children with CP should continue on a regular basis and be integrated into the child's lifestyle so that any benefits can be maintained. Children and adolescents with CP need opportunities to “work out” and maintain the levels of physical functioning achieved during physical therapy and exercise activity interventions. This appears to be an easy recommendation but is extremely difficult to accomplish in everyday life. Fun, enjoyment, and opportunities for social interactions were considered facilitators of engaging in physical activity for children and adolescents with CP.47 The benefits of physical activity also were identified as facilitators.47
However, several personal and environmental barriers to fitness and physical activity have been identified by children and their parents.47 First, maintenance of moderate to vigorous levels of intensity of physical activity is challenging for children and adolescents with CP. Second, it is challenging for children with CP to lead an active lifestyle. It might be unrealistic to expect a family with a child with CP to meet the guidelines of moderate to vigorous physical activity of 30 minutes of activity 5 days per week. Not only does the child's physical disability impose restrictions, but parents themselves may experience high stress, time constraints, and financial and psychological burdens that may impede their ability to commit to such an intense fitness regimen.48 Barriers making the use of community fitness programs challenging for families include a lack of trained staff, inaccessible physical environments, and significant challenges with finding information about the programs.49
In summary, although early results were promising, the field has not been very successful in increasing the long-term cardiorespiratory fitness and muscle strength of children and adolescents with CP. We cannot assume that the short-term improvements in cardiorespiratory fitness and muscle strength observed after intervention translate into improved functional abilities or influence health over the long-term. For children and adolescents with CP and their families, there are many factors that make it difficult to incorporate moderate and vigorous levels of physical activity into their daily lives.
The recent interest in reducing sedentary time,41 while encouraging a whole-day approach to physical activity,21,50 introduces a new framework for designing exercise interventions for children with CP. The concept of concurrently increasing physical activity and decreasing sedentary activity may be beneficial for children and adolescents with CP, and the reduction of sedentary behavior may be a more feasible intervention for children and adolescents with more significant movement limitations.
What Do We Know About Sedentary Behavior in Children and Adolescents With CP?
The literature discussing the importance of studying sedentary behavior emphasizes the importance of evaluating the continuum of light- to vigorous-intensity movement behavior during a daily 24-hour cycle of movement activity. This approach is different from exclusively focusing on moderate to vigorous physical activity intervention programs, which occurs for only 5% of the day. Emerging evidence suggests that increased sedentary behavior time is distinctly different from a lack of moderate to vigorous physical activity and has independent and qualitatively different effects on human metabolism, physical function, and health outcomes.16,51–55
A common categorization of physical activity uses the terms “sedentary,” “light,” “moderate,” and “vigorous” to describe specific intensity zones in a continuum from rest to high-intensity activity. The Table provides operational definitions of these terms and includes common examples of each physical activity intensity category.56 The metabolic equivalent of task (MET) used in this table is a physiological measure expressing the energy cost of physical activities and is defined as the ratio of metabolic rate during a specific physical activity to a reference metabolic rate (1 MET), set by convention at 3.5 mL O2·kg−1·min−1.
Operational Definitions of the Activity Continuum
The definition of sedentary behavior has evolved over time (Box 1). Previously, being sedentary meant a lack of moderate to vigorous physical activity. For example, if individuals were not classified as meeting the physical activity guidelines for moderate or vigorous activity, they were described as being sedentary, and this term included light activity.57,58 According to the Sedentary Behaviour Research Network, sedentary behavior needs to be distinguished from light physical activity.59
Box 1. Evolution of Definitions of Sedentary Behavior
2010. Sedentary behavior should be defined as the muscular inactivity rather than the absence of exercise.63
2011. The origins of the word “sedentary” hint at a simpler, more workable definition. The word “sedentary” derives from the Latin verb sedere (to sit). When sitting or lying, the majority of the body's largest muscle groups are under relaxation; in contrast, when standing, even if still, a large proportion of the body's musculature is under tension. Therefore, any nonexercise activity that involves sitting or lying can be considered sedentary.64
2012. Sedentary behavior is any waking behavior characterized by an energy expenditure of ≤1.5 METs while in a sitting or reclining posture.59
A recently published standardized definition of sedentary behavior is any waking behavior characterized by an energy expenditure of ≤1.5 METs while in a sitting or reclining posture.59 This definition of sedentary behavior includes 2 components: posture (sitting or reclining) and energy expenditure (expressed in METs). Static standing is not considered sedentary behavior because a large proportion of the body's muscles are active during standing.60–62
Sedentary time also has been described as muscular inactivity (such as in sitting and lying down) rather than the absence of exercise.63,64 For adults with typical development, there are few exceptions in which an individual can be sitting or lying down but still have a high enough level of energy expenditure (eg, riding a bike) to be considered nonsedentary. For the general population, the definition of sedentary behavior is based on the fact that during sitting and lying down, there is no muscular activity in the large muscles and individuals require very low energy demands. Therefore, posture, energy expenditure, and muscular inactivity are the 3 important factors represented in the definition of sedentary behavior (Box 2).
Box 2. Three Important Factors Represented in the Definitions of Sedentary Behavior
Posture (sitting or reclining)
Energy expenditure (≤1.5 METs)
Muscular inactivity
Are the Current Definitions of Sedentary Behavior Applicable to Children and Youth With CP?
Definitions of sedentary behavior developed for the general population may not extrapolate directly to children and adolescents with CP. Neuromuscular deficits noted in CP include atypical muscle tone, impaired coordination, challenges with muscle co-contraction, balance impairments, and coordination and sensory deficits.65,66 In addition, the sequencing of multiple muscle action is impaired, and there is a high level of coactivation of agonist and antagonist muscles at a joint,65,66 leading to impaired postural control in some individuals with CP.60,61 The degree of movement severity is extremely variable among people with CP, and it is likely that there is heterogeneity in their energy expenditure and muscular activity in different postures, dependent on their degree of motor impairment and type of muscle tonus.
To date, only 2 studies evaluating children with CP have looked at sedentary behavior according to the postural aspect of the definition of sedentary behavior.59 Maher et al33 reported that sedentary activities, such as television and computer use while sitting, were very similar in children and adolescents with and without CP. Pirpiris and Graham67 reported that children with CP spend more time sitting and, by definition, are more sedentary compared with their peers without disabilities. An inverse relationship was observed between severity of disability and time spent in an upright position (standing or walking). The average upright time was 5.6 hours for children without disabilities versus 5.1, 2.5, and 0.5 hours for children with spastic hemiplegia, spastic diplegia, and spastic quadriplegia, respectively. This very limited evidence related to the postural component of sedentary physiology suggests that children with CP are sedentary using the postural (sitting) component of the definition. But are they really sedentary in sitting in terms of energy expenditure and muscular inactivity components of the definition?
The motor impairments that characterize CP create challenges for effective and efficient movement, coordination, and balance. Therefore, some children with CP use increased intentional muscular activity to maintain sitting—it is hard work! In addition, the atypical muscle tone (eg, spasticity) present in most children with CP likely increases energy expenditure during sitting. Given the range of impairments and types of CP (spastic, ataxic, or dystonic), the patterns of energy expenditure and muscular activity differ across different levels of motor involvement and need to be systematically investigated. Because children and adolescents with CP have intentional and nonintentional muscular activity, we cannot assume that children with CP are “sedentary” while sitting. Perhaps the energy and muscular demands required for some individuals to maintain their balance in sitting are high enough to define sitting as nonsedentary. Likewise, the caloric demands of children with dyskinetic cerebral palsy suggest that even though their self-initiated mobility is limited, their constant involuntary posturing is nonsedentary. This shift in thinking creates measurement challenges because sedentary behavior in children with CP has been traditionally measured via self-report of television viewing33 or time recorded in sitting.67 These might not be valid proxy indicators of sedentary behavior because, first, these children may engage in other activities while watching television and, second, sitting might not be a sedentary activity for some individuals with CP.
What about standing—is standing nonsedentary using the present definition? Children with CP who walk without an assistive device can maintain their standing position using large muscles. Nashner et al65 demonstrated that the large muscles in children with CP are active during standing. Therefore, standing cannot be seen as sedentary behavior. However, for children who use standing devices or walkers, we do not know how many muscle groups are active while standing. Some children might use their upper extremities and device to maintain their position, resulting in less muscular activity of large muscles in the legs. What about standing frames? For a child who stands in a supported standing frame, the muscles might be less active, resulting in a lower energy demand. Some children may have muscular activity in their legs and trunk while standing in a standing frame, and other children may be fully supported by the straps and the frame, resulting in muscular inactivity. There is currently no evidence regarding which children with different types of CP are using their muscles during standing (with and without support) and the extent of their muscular activity. If the muscles are active while standing in a standing frame, it could be a useful strategy for decreasing sedentary behavior for children with more severe disabilities, who otherwise may have limited opportunities to spend time in an upright position.
It is important to try to “disentangle” the 3 important factors represented in the definition of sedentary behavior (posture, energy expenditure, and muscular inactivity) for CP. For the general population, the relationships among the 3 variables are easier to hypothesize than with people with CP. It is essential that foundational knowledge regarding the relationships be obtained by studying each of the parameters in people with CP. For example, published MET thresholds and values for children and adolescents with CP are not available, and an evaluation of energy consumption during different movement activities among children representing different levels of motor impairment would provide invaluable information about the actual energy expenditure in different postures. Electromyographic (EMG) recordings could be used to assess muscular activity in different positions and using different supportive devices. Combining the energy expenditure and EMG information with descriptive information about supports and assists used would provide an understanding of the interaction among posture, energy expenditure, and muscular activity in children with CP with different levels of severity.
Research Priorities and Future Directions
For clinicians who are interested in the whole picture of physical activity, it is important to distinguish sedentary behavior as more than the absence of moderate to vigorous physical activity and to include consideration of the parameter of light physical activity. Sedentary behavior in children has been measured in a number of ways, both objectively and subjectively. Subjectively, sedentary behavior has most frequently been measured by self-report or proxy using activity questionnaires. Objectively, accelerometers have become the standard method of measurement to collect information regarding the intensity of movement. Many accelerometers indicate whether someone is sitting or standing—an important distinction when measuring sedentary activity. However, as recently discussed by Innes and Darrah,68 these measures have limitations and have not yet been validated for use with children with CP. More research is needed for clinicians to feel confident that these tools provide a valid measurement of sedentary behavior with this population.
To date, efforts to improve the long-term health of children with CP have focused primarily on moderate to vigorous physical activity and have paid little attention to the mounting evidence to support redressing sedentary behavior as a distinct behavior related to health. Both ends of the activity continuum need to be considered and evaluated. With large amounts of sedentary time, and often low capacity to be active at moderate to vigorous activities, children and adolescents with CP may benefit from physical activity recommendations that focus on decreasing sedentary time and encouraging light-intensity activities. In clinical practice, this could mean both increasing fitness levels and finding ways to limit the total time spent in sedentary pursuits, ensuring that prolonged periods of sedentary time are broken up with bursts of movement and light activity. Two distinct behaviors and their effects have to be considered: (1) the benefits of regular moderate- to vigorous-intensity physical exercise and (2) the risks of too much sedentary time. Just as in the general population,22 interventions to decrease sedentary behavior and increase physical activity are equally important. Focusing on the nonexercise part of the activity continuum involves interventions to increase breaks in sedentary time and replace sedentary activities with light-intensity activities. This focus results in a whole-day approach to activity promotion (Figure). When addressing nonexercise and light physical activity, simple, succinct messages regarding physical activity may be easiest for the therapist. Examples of short, straightforward messages are “sit less, move more” and “cut down on screen time.”
Example of a whole-day approach. Activities that constitute sedentary behavior have not yet been verified for children with cerebral palsy. HRmax=maximum heart rate.
Optimal patterns of activity and sedentary behavior in children and youth with CP require evaluation. Understanding the balance between encouraging moderate- to vigorous-intensity exercise activities and decreasing sedentary behavior by introducing light-intensity activities seem fundamental to positively influence metabolic and health consequences. The current paradigm of physical activity and exercise used for children and youth with CP needs to be reframed, and the benefits of instituting strategies to reduce sedentary behavior need to be evaluated.
Prior to conducting research on the effects of decreasing sedentary behavior, we need to gather foundational knowledge regarding the “face” of sedentary behavior in children with CP. The physiological mechanisms, postures, activities, and energy expenditure levels that represent sedentary behavior in children and youth with CP may be very different from those described for the general population; they also may be different for children with different functional mobility levels and predominant types and distribution of muscle tone. The concept of decreasing sedentary behavior opens the possibility of innovative intervention options to optimize the functional abilities of children and youth with CP, but a clear understanding of how to define sedentary behavior with this population is necessary before appropriate interventions can be designed and implemented.
Conclusion
For decades, exercise professionals have been emphasizing the need for structured moderate to vigorous exercise as the guiding tenet of physical activity and exercise program design for children and adolescents with CP. Intervention recommendations for this population must now be broadened to include reducing sedentary time and encouraging light-intensity activities. To maintain effective levels of physical activity, exercise programs need to be made accessible and feasible for children and their families. To fully appreciate the importance of decreasing sedentary behavior, we need to build foundational knowledge about definitions and classifications specific to individuals with CP. Let us stop being idle and get active!
Footnotes
Dr Verschuren had the idea for the article. Dr Darrah, Dr Novak, Dr Ketelaar, and Dr Wiart helped Dr Verschuren during a consensus round with the outline of the manuscript. Dr Verschuren and Dr Darrah wrote the first draft of the manuscript. Dr Verschuren revised drafts of the manuscript and had final say on its submission. Dr Novak, Dr Ketelaar, and Dr Wiart also assisted in revision of the manuscript.
- Received May 31, 2013.
- Accepted September 25, 2013.
- © 2014 American Physical Therapy Association
References
Issue highlights
- Article
- Abstract
- Fitness and Children With CP
- What Works and What Does Not for Improving the Fitness of Children and Adolescents With CP?
- What Do We Know About Sedentary Behavior in Children and Adolescents With CP?
- Are the Current Definitions of Sedentary Behavior Applicable to Children and Youth With CP?
- Research Priorities and Future Directions
- Conclusion
- Footnotes
- References
- Figures & Data
- Info & Metrics