Physical activity (PA) is defined as “any bodily movement produced by skeletal muscles that results in energy expenditure.”1(p. 126) PA provides numerous health benefits to persons with and without disability.2 Persons with disabilities are known to have lower PA than persons without disabilities.3 Cerebral palsy (CP) is a condition for which PA, and especially exercise, has been strongly promoted, largely to prevent associated secondary conditions.4–8 We now explore what is known about engagement in PA and exercise participation in children and youth with CP.
Children and adolescents with CP are known to have a lower level of activity than peers without disabilities.9,10 They had significantly less up time,9 fewer daily step counts have been reported, and daily walking activity decreased with functional ability level.10 Similarly, young children with CP who were ambulatory were not participating in activities that provided enough intensity to reap the health benefits of PA.11 Also, activities chosen were of slower tempo compared with those chosen by their peers without disabilities.12,13 Others have identified a much larger proportion of sedentary participants with CP (29%) compared with an able-bodied comparison group (10%).14 In addition, on average, PA scores decrease during the adolescent years after a peak between the ages of 10 and 12 years, and adolescents adopt a more sedentary lifestyle during their second decade.14 Studies conducted around the world15–19 have also demonstrated that adolescents with CP are less active than their peers. However, most of these data come from studies in which participants were not analyzed by the level of motor function or were part of a larger disability cohort. Maher et al12 investigated PA patterns of adolescents with CP aged 11 to 17 years. The least physically active response on a self-report measure was consistently reported, and they reported lower average levels of PA compared with age-matched controls.12 They found a strong association between overall PA level and gross motor function, such that more PA is associated with higher levels of motor function. They also demonstrated a significant inverse relationship between PA and age.12 No significant associations were made between PA and sex; however, a trend of more PA participation by males was seen, when compared with females. Among adolescents without disabilities, males have more PA compared with females for all types of activity.20 A limitation to these previous studies is the lack of investigation across all Gross Motor Function Classification System (GMFCS) levels21; the focus has been placed on GMFCS levels I, II, and III,9,10 or on subjects who can ambulate11 in most studies except for one.12
In contrast to PA, there is little information about exercise participation and activity selection of youth with CP. Although Maher et al12 provided ranking of selected activities, there is no published research on the types and rates of exercise participation of adolescents with CP across all GMFCS levels.22 This information is essential to develop a set of PA guidelines allowing physical therapists to tailor PA and exercise programs, that have an added health benefit specific to children based on their GMFCS level and gender to promote adherence to the program. Health promotion initiatives specific to youth with CP are needed to further encourage participation. It is also important to understand the proportion of teens with CP who are and are not meeting the current recommendations set forth by national agencies such as Health Canada.23 The current recommendations are 60 minutes of daily moderate PA and 30 minutes of daily vigorous PA.
The primary purposes of this article are to (1) describe the types of exercise participation of adolescents with CP by sex and GMFCS level; (2) describe the weekly duration of stretching, strengthening, and cardiovascular exercise and to determine effects of gender and GMFCS level; and (3) determine how the adolescents' level of activity compares with national health guidelines. A secondary purpose was to examine activity participation over time.
The data reported here were obtained from the first and final data collection points of a 4-year prospective cohort study called the Adolescent Study of Quality of Life, Mobility, and Exercise (ASQME).
Setting and Participants
Participants in the ASQME were recruited from the Ontario Motor Growth (OMG) study,24 which followed a stratified random sample of 657 children with CP attending 1 of 19 publicly funded children's rehabilitation centers in Ontario, Canada, between 1996 and 2001. The OMG cohort is considered to be population based because each of the centers serves the majority of children with CP in each geographical area. Stratification was based on the GMFCS level21 and age; therefore, this cohort is not necessarily representative with respect to those factors.
All OMG participants who were 11 years of age or older in April 2002 (n = 343) were invited to participate in ASQME. Seventy-one percent (n = 244) of the youth and families agreed to participate, and 230 were enrolled for the first data collection point. Participants completed the Exercise Questionnaire at each of 4 annual data collection points; however, only the first and fourth are used in this article. ASQME participants did not differ from eligible OMG participants who did not take part in ASQME on all background demographic characteristics except for maternal education; ASQME participants had mothers with higher education. Overall, the ASQME sample comprised 104 girls (45.2%) and 126 boys (54.8%) with mean ages of 14.7 and 14.8 years (SD for both = 1.7 years) at the study onset. All participants were between the ages of 11 and 18 years at the beginning of the study. Table 1 contains the distribution of gender and age by GMFCS levels. The ASQME study was approved by the Research Ethics Board at McMaster University. Written informed consent was obtained from caregivers, and written assent was obtained from the adolescent participants before data collection.
Of the many measures used in ASQME, the following 2 are relevant to this article: the GMFCS and the Exercise Questionnaire. The GMFCS21 is a standardized, reliable, and valid system to classify motor function of children with CP aged 2 to 12 years. A version for youth aged 12 to 18 years was validated as part of the ASQME work.25 Using this system, individuals are classified based on their self-initiated movement and need for assistive technology and wheeled mobility. Individuals are classified into levels I to V, from level V in which the person has very limited mobility to level I in which the person is able to walk and run, but is limited in more advanced motor abilities. Trained and reliable therapists classified ASQME participants using the GMFCS; all therapists achieved 80% or greater agreement with a criterion.
As done in other population-based research,26 we used a questionnaire to collect data on PA in the form of exercise. We defined exercise as activities that involve stretching, strengthening, or physical effort. We defined activities that involve effort as being associated with the heart working harder and faster, breathing to be deeper, and with the body perspiring or sweating. Following a design by Sallis et al,27 we developed the Exercise Questionnaire to be completed by either the adolescent alone or the parent and adolescent together. We generated a list of activities from the Previous Day Physical Activity Record,28 an instrument that was developed for youth, but we regarded that to be too complex for the sample that we were studying due to the cognitive load associated with the questionnaire. We also added items that were appropriate for youth with CP through consultation among expert investigators involved in the study; these items were confirmed through pilot testing with youth with CP, which supported the content validity of the questionnaire. As others have done,29 we asked each participant to read through the list of activities and then to (1) check “yes” for any activity that they had performed in the previous week, (2) indicate the number of times that they performed that activity in the previous week, (3) write down the number of minutes, on average, for each occasion, and (4) indicate the intensity of the activity, on average, from a choice of light, medium, or hard, based on definitions provided on the questionnaire (Appendix). Participants either completed the questionnaire alone (23.6%) or with help from family members (48.2%) or the questionnaire was completed by parental proxy (28.2%). The results were not significantly different by the method of administration for light and moderate exercise; however, they were significantly different for vigorous exercise. Questionnaires completed by proxy reported less vigorous exercise compared with questionnaires completed by the participant alone or with help. The majority of questionnaires completed by proxy was for participants at GMFCS level V and so this result is not surprising.
The exercise data were first summarized by describing the most frequent types of exercise participation by gender and GMFCS levels. Weekly duration of exercise participation in stretching and strengthening was determined by multiplying the frequency and duration of these activities. Light, medium, and hard cardiovascular exercise participation was determined by summing the products of frequency and duration across all responses, other than stretching and strengthening. All weekly duration activities (in minutes) were summarized by means, standard deviations, medians, and ranges by gender and GMFCS levels. A 2-way analysis of variance was conducted to determine the effect of gender and GMFCS level on stretching and strengthening and on light, medium, and hard cardiovascular exercise; the Tukey test was used for post hoc testing. To determine how the adolescents' level of activity compares with national health guidelines, the data were collapsed to establish proportions of our sample who participated in none, some, or the recommended amount for moderate (our medium category) or vigorous (our hard category) activity. A χ2 analysis was used to determine the effect of gender and GMFCS level on categorization of participation. A t test was conducted between the total duration of stretching and strengthening, and participation in light, moderate, and vigorous exercise between time 1 and time 4. A χ2 analysis was done to determine whether classification of none, some, and recommended levels of moderate or vigorous exercise participation differed over the 4 years of the study. SPSS version 16 (SPSS Inc, Chicago, Illinois) was used for analysis. An α value of .05 was established for statistical significance.
Table 2 contains the relative frequencies of participation in various activities by gender and GMFCS level. A wide variety of activities were reported by the adolescents in the study, and only the 5 most frequent responses per level and gender are recorded.
Table 3 contains a summary of the weekly duration of participation in stretching and strengthening and in light, moderate, and vigorous cardiovascular exercise. Two-way analyses of variance yielded the following statistically significant effects. For stretching, there was a significant interaction of GMFCS level and gender (F = 2.63, df = 4, P = .04) and a significant main effect of GMFCS level (F = 9.31, df = 4, P < .001). Participants at level V had significantly longer stretching durations than those in all other GMFCS levels (P < .004). Female participants at level V engaged in significantly more stretching than male participants at level V, accounting for the significant interaction. There was a significant main effect of GMFCS level for light intensity exercise (F = 2.45, df = 4, P = .05), with participants at level V having significantly lower levels of light exercise than those at level I. There was a significant main effect of GMFCS level for moderate-intensity exercise (F = 3.26, df = 4, P = .01) with participants at level IV (P = .04) and V (P = .05), having significantly less moderate exercise than those at level III. There were no significant effects for strengthening and vigorous exercise.
Figures 1 and 2 contain the proportion of the sample who participated in none, as characterized by 0 reported minutes; some reported minutes between 1 to 419 for moderate PA and 1 to 209 minutes for vigorous PA or the recommended amount, 420 or more minutes for moderate PA, and 210 or more minutes for vigorous PA. Health Canada's recommendations for moderate activity are being met by approximately 14% of males and 3% of females at level I, 11% of males and 14% of females at level II, 25% of males and 12.5% of females at level III, 3% of males and 0% females at level IV, and 0% of males and 5% of females at level V. Overall 9.5% of males and 6.5% of females met the current recommendations for moderate activity. In terms of vigorous activity 21% of males and 15% of females at level I, 13% of males and 5% of females at level II, and 19% of males and 0% females at level III, 6% of males and 10% of females at level IV, and 0% of males and 5% of females at level V are meeting the recommendations set forth by Health Canada. Overall, 11.7% of males and 7.8% of females are meeting the recommendations for vigorous exercise.
The χ2 analysis of the effect of gender on classification into none, some, or recommended was nonsignificant for both moderate and vigorous exercise. Similar analysis testing the effect of GMFCS level was significant for moderate (χ2 = 27.2, df = 8, P = .001), but not vigorous exercise. Participants at levels IV and V were less likely to engage in moderate activity than those at levels I to III.
The t tests of the total duration of stretching, strengthening, and vigorous exercise were nonsignificantly different between time 1 and time 4. Significant differences were obtained for light and moderate exercise (t = 2.37, df = 393, P = .02; and t = 2.78, df = 353, P = .006) with mean reductions of 31 and 72 minutes per week, respectively. The χ2 test of the difference in classification of none, some, or recommended was significant for both moderate and vigorous exercise (χ2 = 15.3, df = 8, P = .05; and χ2 = 15.7, df = 8, P = .5) with a shift from the higher categories to none over the 4-year period. By time 4, 68% and 84% of participants took part in no moderate or vigorous PA, respectively; this effect was largely independent of GMFCS level.
DISCUSSION AND CONCLUSION
This report provides the first published information on rates of exercise participation among adolescents with CP across all GMFCS levels. In our study, males did not exhibit more exercise participation than females; however, participants with more gross motor function, regardless of gender, did report greater exercise participation than those with less motor function. Consistent with previous research on PA, exercise participation decreased over the 4-year period of the study. Overall, participation rates were low. Of concern, these results may reflect an overestimation of exercise participation due to the use of a self-report measure and social desirability bias or recall bias.
To assist with interpretation of the results with respect to type of exercise participation, we rely on the work of Maher et al.12 In their study, swimming was more highly ranked for adolescents with CP than for those without. In our study, swimming ranked in the top 3 activities in all categories except for females at levels III and V. Maher et al12 reported that activities such as basketball, dancing, and riding a bike were more highly ranked by adolescents without CP. Some participants in each GMFCS level and gender category (except for females at level V) in our study participated in these activities. Walking was the most frequent activity of participants in GMFCS levels I, II, and III, and the second most frequent among those at level IV; it was also the second most highly ranked activity in the study by Maher et al.12 In our study, participants identified the following activities that are not reported by Maher et al12: hockey (usually sledge hockey), baseball/catch, wheeling, bowling, and volleyball. Also, other activities of lower frequency, such as martial arts and soccer, were reported in our study; a full list of the reported activities can be obtained from the corresponding author. Although it is difficult to compare these patterns of exercise participation with other studies, it is possible that at least some adolescents participated at higher intensities than in the study by Maher et al.12 Pediatric physical therapists should use this information in PA and exercise prescription to help determine the types of sports or activities that interest youth with CP. This also may promote adherence to such programs because if the activity is interesting and stimulating the youth may be more inclined to continue their participation over time through adulthood. Of concern in our study is the relatively isolated nature of the activities engaged in by only a small proportion of female participants at level V as can be seen in Table 2. The activities reported by these participants are not of the same intensity as the activities reported for males at the same GMFCS level, and fewer people reported any activity compared with other severity levels. This is of concern due to the secondary impairments associated with this GMFCS level, such as deficits in force production that could be relieved through participation in PA or exercise.
The significant main effect of GMFCS level on stretching may be related to the role that stretching might play in helping to preserve the range of motion and delay or avoid the need for surgical interventions.30 An inverse relationship between stretching and function emerged. Formal stretching programs were reported more by participants with higher levels of impairment; this may be due to the emphasis on stretching in physical therapy sessions to delay surgery; it may also be possible that some activities reported by participants include minimal stretching components within the exercise. Overall, the reported levels of stretching were lower than expected; maintaining range of motion and increasing muscle extensibility could benefit all adolescents with CP regardless of the level of impairment, although this assumption is controversial.30
More than one half of the participants performed no strengthening exercise across all GMFCS levels and both genders. This is especially troubling because individuals with CP have primary and secondary deficits in force production, which can lead to further deconditioning.6 As recommended by Damiano,4 individuals with CP need to be encouraged to participate in PA, including strengthening. Aside from producing increases in strength,31 isotonic strength training has been shown to promote functional gains that can be maintained even without further training,32 and strength training in youth may prevent deterioration of health status.32 Strength training also has the potential to improve gait function.31
Cardiovascular exercise participation rates were low for both moderate and vigorous exercise, particularly at levels IV and V. Children with CP are known to display low levels of cardiorespiratory fitness based on reduced peak Vo2 and higher submaximal energy demand of walking33–34 and displaying excessive energy expenditure for set walking speeds.6,34–37 It is also troubling that there was a decrease in participation in both moderate and vigorous PA over the 4-year period of the study. To our knowledge, no other study has identified a decline in PA participation of adolescents with CP over time. This is particularly problematic because levels of activity exhibited between the ages of 9 and 18 years can significantly predict the level of PA engaged in during the adult years.10 If this low level of activity in the adolescent years persists into adulthood, it could lead to further secondary impairments and chronic health conditions associated with inactivity.
Of note, a large proportion of the adolescents from both genders are doing some activity but not enough to meet Health Canada's guidelines. Perhaps there is the opportunity to increase participation with the right programming initiatives and directed health promotion efforts. Campbell38 demonstrated a need for research on how to interrupt the cycle of increasing disability and deconditioning that is associated with chronic health conditions and promoting PA practices and programs that require children and youth to take responsibility for their own personal health and fitness before the transition out of pediatric care.
In addition to possible inflated estimates of the previous week's exercise participation levels, a second limitation of the study is a lack of definitive information about the reliability of our Exercise Questionnaire. Three attempts were made over 3 years to determine test-retest reliability. First, 300 flyers were distributed to children and youth with disabilities in the Thames Valley District School Board. Four youth agreed to participate; 1 had CP. Second, 189 letters of invitation were distributed to children and youth with disabilities and receiving services through the Thames Valley Children's Centre. Five youth agreed to participate; 2 had CP. Finally, attempts were made to obtain second estimates of exercise participation by asking participants in the ASQME study; 6 responses were received. This total data set from 9 participants yielded a low intraclass correlation coefficient, primarily due to lack of variability in the data (ie, exercise participation was low). Nonetheless, there was no significant difference between test and retest scores. The difficulty obtaining a sample to examine test-retest reliability is interpreted as another indicator that adolescents with CP are not interested in PA and exercise. Nonetheless, evidence from the 7-Day Physical Activity Recall and the Godin-Shephard Questionnaire, as indicated by Pearson correlation coefficients of 0.77 and 0.81, respectively, suggest that children and youth developing typically, who are older than grade 5 age, are able to report on participation in PA for the previous week.39
Our work suggests that future work should focus on determining barriers and facilitators to PA in adolescents with CP and investigating strategies to promote PA and engagement in exercise of sufficient frequency, duration, and intensity to yield health benefits. A particular emphasis needs to be made to ensure that adequate PA levels are continued into adulthood. In conclusion, the lower than acceptable and declining exercise participation in adolescents with CP that were observed in this study clearly indicate that renewed and sustained efforts to promote PA and exercise participation are required.
We thank the ASQME team (Peter Rosenbaum, Robert Palisano, Steven Hanna, Dianne Russell, Stephen Walter, and Barbara Galuppi) for their support and access to the data. We also thank Jan Willem Gorter of CanChild for his review and helpful comments on the final draft of this manuscript.
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The chart discussed later asks about the exercises you did last week. By “exercise,” we mean activities that involve stretching, strengthening, or physical effort. Activities that involve effort or exertion cause the following things: (1) the heart works harder and faster, (2) breathing is deeper, and (3) the body perspires or sweats.
The first column in the chart asks you to think about and circle the number for the exercises you did over the past week. There is some space for you to write in the other “sports,” or “exercises” that you did.
The second column in the chart asks you to write-in the number of different times in the past week you did each of the exercises listed. If you did not do exercise at all, just leave the space blank.
The third column in the chart asks you to write-in the average amount of time (in minutes) you spent doing each of the exercises listed, each time. You will not need to put anything in this column for the exercises you did not do at all last week.
The fourth column in the chart asks you to write-in how hard you worked on average when you did each exercise last week. Again, you will not need to put anything in this column for the exercises you did not do at all last week.
When you are thinking about how hard you worked, please choose light, medium, or hard according to the descriptions below.
Light: normal heart rate and breathing, no sweating
Medium: some increase in heart rate and breathing
Hard: heart working hard, breathing very deep, sweating
Keywords:© 2010 Lippincott Williams & Wilkins, Inc.
adolescent; cerebral palsy; exercise; female; human movement system; longitudinal study; male; physical activity; muscle stretching exercise