Abstract
Background Despite the health benefits of regular physical activity, children with cerebral palsy (CP) are thought to participate in reduced levels of physical activity.
Objective The study objective was to assess physical activity and determine the proportion adhering to the recommended 60 minutes of moderate-to-vigorous physical activity (MVPA) daily in independently ambulant children and adolescents with unilateral CP.
Design This was a cross-sectional study.
Method Children (N=102; 52 boys, 50 girls; mean age=11 years 3 months, SD=2 years 4 months) with spastic hemiplegia classified at Gross Motor Function Classification System (GMFCS) levels I (n=44) and II (n=58) recorded physical activity over 4 days using an accelerometer. Activity counts were converted to daily and hourly time spent inactive and in light physical activity or MVPA using uniaxial cutpoints (inactive: ≤100 vertical counts·min−1, light: 101 to 2,295 vertical counts·min−1, MVPA: ≥2,296 vertical counts·min−1) and recorded step counts. Differences between groups were examined using t tests.
Results Of a potential 396 days, 341 days (86%) were recorded. The average wear time was 11:44 (SD=1:56) hours. On a typical day, participants recorded 438 (SD=234) counts·min−1, took 7,541 (SD=3,894) steps, spent 8:36 (SD=1:09) hours inactive, spent 2:38 (SD=0:51) hours in light activity, and spent 0:44 (SD=0:26) hours in MVPA. Only 25% of participants met the recommended level of MVPA on at least one day. Physical activity was highest in boys (versus girls), in children (versus adolescents), and on weekdays (versus weekends).
Limitations Participants were limited to children with unilateral spasticity who were classified at GMFCS levels I and II.
Conclusions The majority of independently ambulant children with unilateral CP did not perform sufficient physical activity to meet public health recommendations.
Modern lifestyles mean that children and adolescents spend an increasing amount of time in sedentary behaviors (eg, watching TV, using computers, using game consoles, or sitting in automobiles), which will typically displace more active behaviors. Increased sedentary behavior in early childhood is concerning, as regular physical activity is essential for children and adolescents; patterns of physical activity acquired during childhood are more likely to be maintained in adult life.1 As a result, many countries have adopted guidelines that suggest all children and adolescents, including, where possible, those with disabilities, should engage in at least 60 minutes of moderate-to-vigorous physical activity (MVPA) every day and limit sedentary screen time to less than 2 hours.2,3 The adoption of recommendations for both MVPA and sedentary time reflects the independent risks associated with these behaviors. Insufficient physical activity and increased sedentary time are often found in tandem but are different constructs, and the detrimental health consequences associated with prolonged sedentary behaviors are thought to be independent of the protective effect of regular MVPA.4
The term cerebral palsy (CP) describes a group of disorders of the development of movement and posture, causing activity limitations, which are attributed to nonprogressive disturbances that occurred in the developing infant brain.5 As CP is the most common physical disability of childhood,6 encouraging regular participation in physical activity is an important health promotion consideration. Physical activity is described as any body movement using skeletal muscles that results in energy expenditure.7 Participation in regular physical activity is important for physical, mental, and social health in children and adolescents,1 with additional benefits for people with CP, including the maintenance of physical function8 and reduced incidence of chronic pain, fatigue, and osteoporosis.9 Despite the known health benefits of engaging in regular physical activity, children with CP are generally less physically active compared with children who are developing typically10 or children with other physical disabilities.11 Only 7% to 11% of children and adolescents with CP reported meeting the recommended levels of physical activity measured using subjective questionnaires.12–15 There are, however, limitations with using parental or self-report questionnaires. These questionnaires are dependent on accurate observation and recall of physical activity, and although formal structured activities (eg, organized sport or physical education classes) may be accurately captured using this method, incidental or unstructured physical activity can be missed.16 The use of questionnaires to record physical activity in children is particularly important to consider, as they typically engage in short bursts of intensive physical activity interspersed with varying intervals of low-to-moderate activity.16
An alternative method to assess physical activity is using objective activity monitors, which are worn by the user over a number of days, recording movement in real time. Accelerometer-based activity monitors are commonly used because they provide a valid method to measure physical activity in children with CP.17,18 These devices detect accelerations in 1 to 3 orthogonal planes (vertical, mediolateral, and anteroposterior), registering movements and storing them as “activity counts,” which can be converted to interpretable output regarding physical activity amount and intensity using cutpoints. There is a growing body of evidence supporting the idea that children and adolescents with CP are not sufficiently physically active as measured using accelerometers.19–25 The triaxial ActiGraph GT3X+ accelerometer (ActiGraph, Pensacola, Florida) is one of the most widely used activity monitors cited in scientific peer-reviewed publications in children who are developing typically26 and is increasingly being used to record physical activity in children with CP.21,25 The triaxial ActiGraph GT3X+ accelerometer is also one of the few accelerometer-based devices used to record physical activity in children with CP with evidence to support its reliability27 and has been validated against oxygen consumption in ambulant children and adolescents with CP.28 This validity study determined that Evenson29 vertical-axis activity counts are able to accurately classify sedentary time (92%) and MVPA (91%) in children and adolescents with CP who are ambulatory.28
The feasibility of using the accelerometers in children with CP was first established in a group of 23 adolescents classified at Gross Motor Function Classification System (GMFCS) levels I to IV.21 In that study, daily MVPA was 30.7 minutes, corresponding to 4.5% of monitoring time, with independently ambulant adolescents (GMFCS I–II) more physically active than those using a walking aid or wheelchair (GMFCS III–IV). Sedentary time has since been assessed using the same type of accelerometer in 17 children and adolescents with CP who were ambulatory (GMFCS I–III) and presented with a mix of motor types and distributions.25 In that study, children with CP were significantly more sedentary and took fewer breaks from sedentary time than matched typically developing controls.
Although these studies provide important information about physical activity in children with CP, there are some potential limitations due to the heterogeneity of the samples and small sample size, as physical activity levels are thought to be influenced by GMFCS and motor distribution.19 It would be useful to explore physical activity in a more homogeneous group of children and adolescents with CP.
The aims of the current study were: (1) to assess physical activity of independently ambulant (GMFCS I–II) children and adolescents with unilateral CP using the triaxial ActiGraph GT3X+ accelerometer and (2) to determine the proportion adhering to the recommended level of MVPA (60 minutes daily). Additionally, this study aimed to examine physical activity and inactivity in this population by comparing: (1) GMFCS levels I and II, (2) children and adolescents, (3) boys and girls, and (4) weekday and weekend activity.
Method
Participants
This article describes a cross-sectional analysis of baseline assessments from 102 children from the “Move it to improve it” (Mitii) Australia study for which recruitment, methods, outcome measures (including psychometric properties of the outcome measures), and analysis have been described in detail elsewhere.30 In brief, this was a randomized, wait-list controlled trial investigating the effects of the Web-based training program Mitii. Participants were aged 8 to 17 years with unilateral CP and had been classified at GMFCS levels I and II (I=walks independently with aids and can climb stairs without a handrail, II=requires upper extremity assistance to climb stairs, but walks independently without aids).31 All children presented with spastic motor type and unilateral distribution of CP (hemiplegia). Because Mitii is primarily an upper limb intervention, children were excluded or delayed if they had undergone upper limb botulinum toxin type A injections or surgery in the previous 2 or 6 months, respectively, or had unstable epilepsy or medical conditions that would prohibit them completing the Mitii training. Written informed consent was obtained from parents or guardians and all participants older than 12 years of age before entering the trial.
Procedure
Participants received a triaxial ActiGraph GT3X+ accelerometer to record physical activity. Each accelerometer was initialized according to manufacturer specifications to record step counts and accelerations at 100 Hz. Accelerometer units were fitted during assessment on an elastic belt that was worn around the waist by the participant. Children were instructed to wear the belt so that the accelerometer unit was positioned on the midaxillary line at the level of the iliac crest on the side of the body least affected by neurological impairment and to wear the device for all waking hours for 4 consecutive days (including 2 weekdays and 2 weekend days, where possible). During this time, parents registered the wear time of the device on an activity diary provided. After 4 days, the device and activity diary were returned for data extraction and analysis.
Data Reduction
Activity counts from the accelerometer were downloaded to a personal computer and manipulated in ActiLife version 6 software (ActiGraph, Pensacola, Florida). Device wear time was validated by visually inspecting the activity diary and comparing data from the diary with the ActiLife output. All representative and complete data (where at least one day of >8 hours of data was recorded each day) were included in the analysis. Activity count values of zero occurring for >20 minutes, determined using software algorithms, were set as nonwear time and excluded from the analysis. Vertical axis activity counts were converted to activity intensity using Evenson cutpoints29 to classify activity counts as inactive (≤100 counts·min−1), light-intensity 101–2,295 counts·min−1), and MVPA (≥2,296 counts·min−1). To account for differences in wear time among participants, activity was normalized to actual monitoring time to calculate minutes per hour, and daily time spent in each activity state was calculated using a 12-hour standardized wear time. The pattern of physical activity throughout a day was determined by plotting the mean vertical axis counts·min−1 for each hour of the day against time (6 am–9 pm), by age group (child <13 years and adolescent ≥13 years), sex, and day type.
Data Analysis
Data were collated in Microsoft Excel 2010 (Microsoft Corp, Redmond, Washington) and analyzed using IBM SPSS version 22 software (IBM Corp, Armonk, New York). Data were examined for normality by visually inspecting the histograms and by performing the Shapiro-Wilk test; all variables were normally distributed. Descriptive statistics were calculated for all variables. The proportion of participants meeting the recommended level of MVPA (60 minutes) on at least 1 recorded day was calculated. Because data were normally distributed and had equal variances, paired (day type) and independent (GMFCS level, age, and sex) 2-sided t tests were calculated. Data are presented as mean (standard deviation); alpha was set at .05.
Role of the Funding Source
All sources of funding were project grants or stipends for researchers. The funding bodies had no involvement in the study design, analysis, or interpretation of data, in writing of the manuscript, or in the decision to submit the manuscript for publication. No conflict of interest, such as financial gain, exists between the authors of this article and the companies producing the equipment, which is the focus of this research. The study was supported by a Queensland Government Co-Investment Program Grant “EBrain” (R.N.B., J.Z.), a Financial Markets Foundation for Children research grant (R.N.B., J.Z.), an Australian Postgraduate Award (L.E.M.), and a National Health and Medical Research Council Career Development Fellowship (R.N.B.; Level 2, no. 1037220), a Smart State Fellowship (R.N.B.).
Results
Participant Characteristics
Children (N=102; 52 boys, 50 girls; mean age=11 years 3 months, SD=2 years 4 months) with spastic hemiplegia classified at GMFCS levels I (n=44) and II (n=58) recorded physical activity over 4 days using an accelerometer. Of the 102 participants enrolled in the study, 99 completed a baseline assessment. Of those who completed the baseline assessment, 91 (92%) returned valid and complete accelerometer recordings. Data were collected for 341 (86%) out of a possible 396 days. The participants with valid and complete accelerometer recordings were children and adolescents with unilateral CP (48 boys, 43 girls; mean age=11 years 3 months, SD=2 years 4 months) classified at GMFCS levels I (n=44) and II (n=47). Personal characteristics are presented in Table 1.
Characteristics of Participants Included in Study (N=102)a
Physical Activity and Adherence to the Recommended Level of MVPA
Physical activity levels and adherence to the recommended level of MVPA are presented in Table 2. On average, participants wore the monitor for 11:44 hours per day (SD=1:56), recorded 438 counts·min−1 (SD=234), took 7,541 steps, spent 8:36 hours (SD=1:09) (72% of recorded time) inactive (corresponding to 43.1 minutes per hour), spent 2:38 hours (SD=0:51) in light activities (22% of recorded time), and spent 0:44 hours (SD=0:26) (6% of recorded time) in MVPA (corresponding to 3.7 minutes per hour) (Tab. 2). Only 25% of participants met the recommended level of MVPA on at least one day (Tab. 2).
Daily and Hourly Physical Activity in Independently Ambulant Children With Unilateral Cerebral Palsy and by GMFCS Level, Age, Sex, and Day Typea
Physical Activity by GMFCS Level, Age, Sex, and Day Type
Physical activity by GMFCS level, age, sex, and day type are presented in Table 2. There were no significant differences in physical activity between children classified at GMFCS levels I and II. Children were significantly more physically active than adolescents. Boys were significantly more physically active than girls. More steps were recorded on weekdays than on weekend days. The pattern of physical activity over a typical day is presented in the Figure. Boys generally recorded higher activity counts throughout the day than girls, and this pattern remained consistent across day types. The pattern of daily physical activity was similar between age groups; however, children were more active than adolescents throughout most of the day (Figure). When comparing by day type, weekdays were characterized by peaks and troughs of activity, with participants demonstrating higher volumes of MVPA at 8 am, 1 pm, and 3 to 5 pm and the most sedentary behavior at 9 am and 7 to 9 pm, whereas weekend MVPA peaked between 10 am and 2 pm (Figure).
Average daily (6 am–9 pm) physical activity patterns by age group (children [n=61], adolescents [n=29]), sex (girls [n=43], boys [n=48]), and day type (weekend days [n=133], weekdays [n=208]). Plotted values are mean activity levels (counts·min−1).
Discussion
Recommendations for healthy levels of physical activity suggest that 60 minutes of MVPA is required on a daily basis for children and adolescents. The results of the current study suggest that the majority of independently ambulant children and adolescents with unilateral CP are not sufficiently physically active to meet these recommendations; only 25% of this population participated in 60 minutes of MVPA on at least one day of monitoring and on average recording 0:44 hours in MVPA. The proportion of children participating in 60 minutes of MVPA daily, although somewhat alarming, is comparable to a study that also utilized uniaxial accelerometers where 26% of children engaged in more than 60 minutes of MPVA on at least one day of monitoring.21 However, despite using objective accelerometers to record physical activity, few children participated in 60 minutes of MVPA on one day of the sampling period and were assessed for daily adherence; the proportion of participants performing 60 minutes MVPA each day would likely reduce further. Currently, the physical activity guidelines stipulate times for MVPA and sedentary time, but it is unclear what role light physical activity has in the health of children. In the current study, children with CP recorded 2:38 hours of light activity on average per day, which, when combined with 0:44 hours of MVPA, may be sufficient to promote long-term health. Considering the role of light physical activity seems particularly relevant for children with CP, where musculoskeletal impairments and altered biomechanics may mean that achieving 60 minutes of MVPA daily is not an appropriate goal. Further research linking physical activity to long-term health outcomes and considering the individual requirements of children with CP seems necessary to determine: (1) what level of physical activity is truly recommended for this population and (2) if a combination of light and MVPA is sufficient to improve health.
Recently, there has been interest in quantifying sedentary time in children with CP.32 Increasing evidence details the negative effects that prolonged inactivity has on cardiovascular and metabolic systems, which appears to be independent of the amount of exercise a person undertakes.33 Sedentary behavior refers to any waking activity characterized by a low energy expenditure (≤1.5 metabolic equivalents) while in a seated or reclining posture.34 If this definition is considered, despite being validated against energy expenditure in children with CP,28 accelerometers cannot truly determine if a person is sedentary because they do not provide a direct measurement of energy expenditure, nor can they describe the posture of the wearer. Furthermore, it is unclear whether a child with CP is, in fact, sedentary while in a seated position because postural instability and the muscle activation required to maintain the posture may result in an energy expenditure greater than 1.5 metabolic equivalents.32
Although more research is needed to define sedentary behavior in children with CP, the current study provides important insights into physical inactivity in this population. Participants in the current study were inactive for 72% of a typical day, and inactivity was highest in adolescents and girls. Previous studies have shown similar findings of physical inactivity; ambulatory children and adolescents with CP were significantly more inactive, taking fewer breaks from sedentary time than typically developing controls25 and spending almost 80% of their time inactive.23,35 Although the participants in the current study were more physically active, these levels are alarming when combined with the low levels of physical activity, especially in the context of these children representing some of the most physically able children with CP. Consistent with published literature,23,24,36 there were no differences in physical activity between GMFCS levels I and II in the current study. However, physical activity levels have been shown to decrease with increasing GMFCS level19,21,37 and with bilateral distribution of motor impairment,19 which would likely result in a greater reduction in physical activity were these children included in the current study.
Ambulatory activity has previously been assessed in children with CP, recording on average 9,586 steps daily (ranging from 10,680 steps for children classified at GMFCS level I to 5,734 steps for children classified at GMFCS level III19 and 6,342 steps per day for adolescents).38 Although research is necessary to validate the step counting feature of the accelerometer used in the current study, our results and previous evidence19,20,38 suggest that children and adolescents with CP are not performing sufficient ambulatory activity to meet the suggested 12,000 to 15,000 steps per day recommended for children who are developing typically.39
Consistent with previous research in children with CP19,37 and children who are developing typically,40 children were more physically active than adolescents. Physical activity was significantly greater in boys compared with girls, which also is consistent in children who are developing typically.41 Although levels of physical activity were similar between weekdays and weekend days, participants recorded more step counts and were more likely to meet the recommended level of MVPA on a weekday, consistent with previous evidence in children with CP19 and children who are developing typically.42 Similar to evidence in children who are developing typically,40 the daily pattern of physical activity differed by day type. Hourly activity counts illustrated that weekday physical activity was characterized by deep peaks and troughs, most likely representing periods sitting sedentary in a classroom, interspersed with free play opportunities during breaks as well as before or after school. Boys appeared to be more active during these breaks, with higher peaks than girls, returning to similar levels of activity during sedentary periods. Weekend activity fluctuated less throughout a typical day. These findings are likely to represent less structured activity compared with weekdays, although boys did exhibit higher weekend activity levels between 8 am and 11 am, suggestive of organized sports or active tasks being performed at this time.
Limitations
There are some potential limitations to this study that must be acknowledged. Compared with physical activity research in children who are developing typically, which often includes hundreds of participants, our participant numbers were small. Obtaining accelerometer data from a larger population would be costly (with units costing US$250 each), and accessing a larger group of children with CP would require coordination with multiple service providers. The exclusion criteria included children with recent upper limb botulinum toxin type A injections but did not consider lower limb interventions, which had the potential to influence physical activity. Additionally, screen time was not recorded, and measurements of physical activity were collected for a maximum of 4 days, which although reliable to record physical activity in children and adolescents with CP,27 may mean that additional activity may have been missed that could have been captured with additional days. Participants also were restricted to those with a unilateral motor distribution to create a more homogeneous sample, limiting the risk of bias. It should be noted that hemiplegia is the common motor distribution, with spastic hemiplegia representing between 21% and 40% of the population with spasticity and 60% with other motor types.6 Further research to confirm similar patterns and levels of physical activity in children with bilateral CP or those who are not independently ambulant would be useful. It should be noted that there is a risk of potentially inflated type I error rate (higher than .05), as multiple t tests were conducted on the same sample.
Clinical Implications
The results of the current study suggest that the majority of independently ambulant children and adolescents with unilateral CP are not sufficiently physically active to meet the recommended level of MVPA, with physical inactivity most problematic in girls, in adolescents, and on weekends. Interventions targeting an increase in physical activity should ideally target these more vulnerable groups. Research suggests that physical activity interventions should identify the barriers to and facilitators of physical activity specific to each individual and adjust interventions to encourage physical activity participation43 This can be a complex process, as many barriers to participation in physical activity have been identified in children with CP and disability more broadly, including personal characteristics such as self-esteem and perceived competence in sports and physical activity; family characteristics, such as lifestyle, available time, positive role modeling, and financial resources; and community support, such as nearby facilities, convenient transportation, suitable activity programs, equipment, and social support.43,44 Clinicians and policy makers need to consider strategies to overcome the barriers to participation in physical activity to promote lifelong health in children and adolescents with CP.
The Bottom Line
What do we already know about this topic?
Despite the known benefits of engaging in regular physical activity, children and adolescents with cerebral palsy (CP) are generally less physically active and spend more time inactive than their peers with typical development. This study sought to assess physical activity in children and adolescents with CP using an accelerometer.
What new information does this study offer?
This study showed that, on average, only 25% of children and adolescents with unilateral CP who are independently ambulant performed sufficient physical activity to meet the recommended level of 60 minutes moderate to vigorous physical activity on at least one day of monitoring. Children were significantly more physically active than adolescents, boys more than girls, and weekday activity was greater than that recorded on weekends.
If you're a patient or a caregiver, what might these findings mean for you?
Although independently ambulant children and adolescents with unilateral CP are some of the most physically able children with CP, physical inactivity still represents a significant problem in this population. Physical inactivity is most problematic in adolescents and girls and on weekends.
Footnotes
All authors provided concept/idea/research design, writing, and consultation (including review of the manuscript before submission). Dr Mitchell provided data collection and analysis and preparation of the manuscript, which contributed toward her doctoral studies. Dr Boyd and Dr Ziviani provided fund procurement.
Ethical approval for the study was obtained by the Medical Ethics Committee of the University of Queensland (2011000608) and The Royal Children's Hospital Brisbane (HREC/11/QRCH/35).
The article was presented at Australasian Academy of Cerebral Palsy and Developmental Medicine Conference; March 11–14, 2014; Hunter Valley, New South Wales, Australia. A poster was presented at the American Academy for Cerebral Palsy and Developmental Medicine Annual Meeting; September 10–13, 2014; San Diego, California.
All sources of funding were project grants or stipends for researchers. The study was supported by a Queensland Government Co-Investment Program Grant “EBrain” (R.N.B., J.Z.), a Financial Markets Foundation for Children research grant (R.N.B., J.Z.), an Australian Postgraduate Award (L.E.M.), a National Health and Medical Research Council Career Development Fellowship (R.N.B.; Level 2, no. 1037220), and a Smart State Fellowship (R.N.B.).
Trial registration number: ACTRN12611001174976.
- Received January 27, 2014.
- Accepted September 24, 2014.
- © 2015 American Physical Therapy Association
References
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