Dodd, Karen J. PhD; Taylor, Nicholas F. PhD; Graham, H. Kerr MD, FRCS(Ed), FRACS
An increasing body of evidence confirms that many children with cerebral palsy demonstrate muscular weakness and that they may benefit from programs designed to increase strength and possibly to improve everyday functional activities. 1–6 In addition to physical benefits, there is some evidence that strength training might lead to psychological benefits for children with cerebral palsy. 7
Self-concept is a central factor in evaluating psychological function and is defined as a person’s perception and evaluation of his or her own characteristics. 8 Self-concept is related to factors such as life satisfaction. 9 Characteristics commonly included when evaluating children’s self-concept are perceived adequacies such as appearance and peer relations as well as perceived competencies in areas such as athletic skill and academic achievement. 10–12 Self-esteem is a closely associated concept that refers to a person’s positive feelings about themselves, the degree of self-liking. Self-esteem can, therefore, be viewed as the evaluative component of self-concept. 13
Relatively little information is available about the self-concept of children with cerebral palsy. However, there is some evidence that children with cerebral palsy have lower self-concept than their unimpaired peers. Researchers have found that young people with chronic disabilities including cerebral palsy have significantly lower self-concept particularly in domains such as athletic competence. 14 In addition, researchers have found that girls with cerebral palsy have lowered self-concept. 15 The results of these previous studies suggest that certain groups of children with cerebral palsy might have lowered self-concept and that interventions to improve their self-concept are worth pursuing. A number of authors have shown that participation in exercise programs can contribute to improved self-concept in populations of unimpaired children, 13,16 obese children, 17 and children with disabilities. 18
Although self-concept is an important psychological factor, only one published study was located examining the effect of an exercise program on the self-concept of young people with cerebral palsy. 7 In that study, the effect of a group gymnasium-based physical activity program on the self-concept of 23 young people with cerebral palsy was documented. Improvements in self-concept were found, specifically in the domain of physical appearance. 7 While that study provides important preliminary information about the effect that exercise may have on self-concept in young people with cerebral palsy, the absence of a control group makes it more difficult to attribute changes to the intervention. In addition, because the exercise program included aerobic and flexibility exercises as well as strengthening exercises, it is difficult to determine the effects of any one component of the program.
Given these considerations, the aim of our study was to use a randomized, controlled trial to test the prediction that participation in a home-based progressive resistance strength-training program would increase the self-concept of children with cerebral palsy.
The study design was a single-blind, randomized, controlled trial. As shown in Figure 1, participants were randomly allocated to either an experimental six-week strength-training group or a nonintervention control group. The dependent variable was self-concept as measured by the Self-Perception Profile for Children. 10 Self-concept was measured at baseline, immediately after completion of the program (week six), and at a follow-up session held 18 weeks after the initial assessment.
To be included, participants had to be between the ages of eight and 16 years, have spastic diplegic cerebral palsy, be able to walk independently with or without a gait aid, and be cognitively able to follow simple commands. Exclusion criteria were a fixed flexion deformity at the knee or hip greater than 25 degrees or fixed equinus of more than 10 degrees, current participation in other management strategies such as serial casting, botulinum toxin, or recent orthopaedic surgery (within the previous 12 months), and participation in a strength-training program within the previous three months. The Hospital and University Human Ethics Committees approved this trial, and written informed consent was obtained for each participant. The 17 children recruited for this study comprised most of the 21 participants of a randomized, controlled trial examining the effects of strength training for children and adolescents with cerebral palsy on improving muscle strength and physical activity. 19
Baseline characteristics were assessed to measure the success of randomization. Characteristics measured were age, height, weight, gender, and the severity of disability as classified by the Gross Motor Function Classification System. 20 A physical therapist who was blind to group allocation took all outcome measures. Blinding was maintained until after the final assessment had been completed.
Self-concept was measured with the Self-Perception Profile for Children, 10 a scale designed to assess children’s perceptions of themselves across the domains of scholastic competence, social acceptance, athletic competence, physical appearance, and behavioral conduct as well as a global perception of their worth or esteem as a person. The scale is suitable for children from third grade to approximately ninth grade, 10 from about eight to 16 years old. The scale has demonstrated good to high retest reliability ranging from r = 0.66 to 0.86 21,22 and evidence of construct validity in populations of children with physical disabilities. 7,23 Standardized instructions for completing the 36-item questionnaire 10 were given to each participant. The questionnaire uses a structured alternative format in which the participant was presented with one positive and one negative statement. The child was then asked to select which of the two statements was most like him or her and whether the selected statement was “sort of true” or “really true.” Each question on the Self-Perception Profile for Children received a score between one and four, with four indicating that the child agreed that a statement consistent with a positive self-concept was “really true” for him or her. Scores for questions in each domain were added and averaged, so that six separate domain scores for self-concept were obtained.
Potential participants were identified by one of the authors (K.J.D.) from the outpatient records of a gait laboratory of a large metropolitan children’s hospital. Participants were randomly allocated by one of the authors (K.J.D.) to either the strength training or control group using a concealed method. Identical pieces of paper were placed in an opaque container, half with the words experimental group and half with the words control group written on them. In another opaque container, the name of each participant was written on a separate piece of paper. Allocation was achieved by drawing a piece of paper from each container. This process continued until all the children were allocated to a group.
After baseline measurements were taken, the young people allocated to the experimental group completed a home-based program of exercises designed to strengthen the major support muscle groups of the lower limb: the ankle plantar flexor, knee extensor, and hip extensor muscle groups. The exercises were bilateral heel raises off the edge of a portable step (height, 20 cm), bilateral half squats using a large inflatable ball (55 cm diameter) placed between the participant’s lower back and the wall to guide the movement, and step-ups on a small portable step. At the first session, a physical therapist supplied the equipment (large inflatable ball, portable step, backpack, and free weights), taught the exercises, and determined the optimal training load to ensure a strengthening effect. The training load was adjusted by adding free weights to a backpack worn by the participant so that the participant could complete between eight and 10 repetitions of each exercise with good form before fatigue. 24,25 Participants were instructed to complete three sets of each exercise three times per week for the six weeks of the program. Participants and their parents were provided with a logbook to record the details of exercises completed at each session. The physical therapist made follow-up home visits to the participant at the end of the second and fourth weeks of the program to make sure that the exercises were performed correctly, to provide advice, and to progress the training load.
Children in the control group did not participate in a progressive resistance strength-training program. All participants, including those in the control group, were instructed to continue their normal daily activities, including school and sports. Participants were also able to attend their normal physical therapy program, provided that therapy did not include a progressive resistance exercise program. Due to the random allocation procedures, it was expected that the amount of physical therapy and the level of sports and physical activity that the children participated in would not be different between the two groups. At the end of the trial, all children in the control group confirmed that they had not participated in a progressive strength-training program during the trial.
To assess the effects of the six-week strength-training program on self-concept, participants in the experimental and control groups were tested immediately after the sixth week. To determine whether the strength-training program had longer term effects, participants in the experimental and control groups were tested again 18 weeks after starting the program. All baseline, six-week, and 18-week measurement sessions were held in the University Movement Rehabilitation Laboratory.
Baseline characteristics were compared in the two groups using the χ2 test, Student t test, or Mann-Whitney U test as appropriate. Mann-Whitney U tests were used to compare change in the experimental and control groups. The Mann-Whitney U test is a nonparametric equivalent of a group by time interaction and was used because the Self-Perception Profile is an ordinal scale. To help interpret results, the retest reliability of the Self-Perception Profile for Children in the control group was assessed over the first six weeks. Reliability was expressed in the units of measurement for the interpretation of group and individual scores 26 and as correlation coefficients [intraclass correlation coefficient (ICC) 2,1]. 27 Analyses were completed using SPSS version 10.0 (SPSS Inc., Chicago, IL).
Demographic details of the 10 children randomly assigned to the strength-training group and the seven children assigned to the control group can be viewed in Table 1. There were no significant differences between the experimental and control groups for age, height, weight, or gender. There was a trend, however, for children randomly assigned to the experimental group to be more physically disabled, as measured by the Gross Motor Function Classification Scale 20 (Mann-Whitney U, Z = 1.88, p = 0.09). All 17 participants completed baseline and six-week testing. One participant in the control group did not complete the 18-week follow-up test due to recent surgery on her lower limbs.
Analysis of the logbooks, which were completed by the participants or their parents, showed that children in the experimental group were adherent to their prescribed program, completing an average of 16.8 (SD 2.6) of the scheduled 18 training sessions and an average of 147.4 (SD 24.7) of the scheduled 162 exercise sets. The 10 repetition maximum strength, represented by the weight added to the back pack, increased significantly within the training group over the six weeks for heel raises (mean increase 4.7 kg; t9 = 4.1, p = 0.003), step-ups (mean increase 4.5 kg; t9 = 3.8, p = 0.004), and squats (mean increase 4.7 kg; t9 = 4.0, p = 0.003). Compared with controls, there was a trend for increased isometric lower limb strength for participants in the strength-training group at six weeks (mean difference 5.5 kg, F1,15 = 2.78, p = 0.12) and at 18 weeks (mean difference 11.1 kg, F1,14 = 4.14, p = 0.06).
There were no baseline differences between the two groups for five of the six domains of self-concept (Table 2). However, for the domain of self-perceived scholastic competence, participants in the experimental group rated themselves higher than those in the control group (Mann-Whitney U, Z = 2.17, p = 0.03).
The results for self-concept can be viewed in Table 2. There were significant differences between the groups for changes in the domain of scholastic competence between baseline and six weeks (Mann-Whitney U, Z = 2.08, p = 0.04) and baseline and 18 weeks (Mann-Whitney U, Z = 2.41, p = 0.016), with the domain appearing to increase in the control group, while tending to decrease slightly in the experimental group. A similar trend was observed for the social acceptance domain at 18 weeks (Mann-Whitney U, Z = 2.14, p =0.03) and approached significance at six weeks (Mann-Whitney U, Z = 1.7, p = 0.08). The athletic competence domain also appeared to increase from baseline in the control group, while remaining relatively unchanged in the experimental group. This comparison approached significance at six weeks (Mann-Whitney U, Z = 1.2, p = 0.23) and 18 weeks (Mann-Whitney U, Z = 1.85, p = 0.07). None of the other interaction comparisons for self-concept approached significance.
The results of retest reliability of the Self-Perception Profile for Children in the control group over six weeks can be viewed in Table 3. Retest reliability in the units of measurement indicated that mean group changes of less than 0.5 units in most domains could be attributed to real change with 95% confidence. The 95% confidence interval in all six domains of self-concept crossed zero, indicating that there was no systematic change between test and retest for these measures. To be 95% confident that real change in self-concept had occurred for an individual, changes would need to be greater than 1.0 unit in most domains. In terms of ratios (coefficients of reliability), five of the six domains demonstrated good reliability, according to the guidelines of Portney and Watkins 28 with ICCs greater than 0.75, while the other domain of social acceptance demonstrated moderate reliability [ICC(2,1) = 0.56].
The results of our study suggest that a relatively short home-based strength-training program can inhibit self-concept in children with cerebral palsy. This unexpected finding is contrary to our hypothesis. It also contrasts with the finding of Darrah et al, 3 who reported that adolescents with cerebral palsy who participated in a community gymnasium-based physical activity program demonstrated improved self-concept in the domain of physical appearance and that trends were evident toward improvement for younger children with cerebral palsy. The reasons for the apparent discrepancy in findings are unclear. One explanation is that changes may have been due to the social interaction provided by the group nature of the Darrah et al trial in contrast to the individualized, home-based setting of our intervention. The group dynamic aspects of gymnasium-based programs such as those of Darrah et al, while likely to be more expensive and somewhat less convenient than our home-based program, could have positive effects on self-concept in young people with cerebral palsy. Another explanation for the findings of our study compared with that of Darrah et al could be that exercise programs have a different effect on the self-concept of younger children compared with adolescents with cerebral palsy. 23 However, there was a large overlap in the age of the children in both studies with a mean age of 14.2 years (range 11 to 20 years) in the Darrah et al trial compared with a mean age of 12.1 years (range eight to 16 years) in our trial.
It seems unlikely that our findings are due to error associated with the measurement procedure. As the results of retest reliability show, systematic change was not detected in any of the six self-concept domains over time and the estimates of measurement variability for interpreting group change reported in the units of measure were relatively small (most less than 0.5 units).
The results of our study suggest that participation in a strength-training program might inhibit perceived competency in academic and athletic skills as well as social acceptance. Why this occurred is unknown. For academic competence, it is possible that the time spent participating in a strengthening program may have meant that the children spent less time on academic activities such as homework and, therefore, may have believed that their scholastic competence had decreased over six weeks. This issue is supported anecdotally by comments made by some of the children in the experimental group. One 11-year-old girl stated “I found it quite hard to fit it (the exercises sessions) in” because she had “school work, homework” to do as well. One of the parents of a 12-year-old boy stated that “being in year six, with quite a lot of homework, it was hard to find the time and we had to make a deliberate effort to do the exercises.” Similarly for social acceptance, the time spent doing an individual strength-training program, most often with the assistance of a parent at home, may have made the children feel that they had less time to interact with their peers and keep up friendships. Therefore, at the end of the program, these children thought their social acceptance had decreased compared with the children in the control group. With respect to the trend of inhibition of athletic competence, the program was by design physically demanding and participation may have highlighted to these children the difficulties that they had in the domain of physical and athletic ability, in contrast to the control group who continued with their usual activities.
No changes were detected in the domains of physical appearance, behavioral conduct, and global self-worth. Examination of the items in these domains suggested that they were unlikely to be changed by participation in a short strengthening program. For example, the items used to assess physical appearance included specific evaluations of their face, hair, height, and weight. Also, the items used to assess global self-worth concern how happy children are with themselves and whether they like the kind of person they are.
It is commonly assumed by many clinicians that children with chronic, often severe, physical disabilities such as those associated with cerebral palsy are likely to have lower self-concept than their unimpaired peers. 29 However, our results suggest that overall both the experimental and the control groups demonstrated a positive self-concept at baseline, six weeks, and 18 weeks. In addition, the mean scores for these children with cerebral palsy, both before and after the strength-training program, were comparable with those documented for young people who are unimpaired. 10 These findings support some of the previous studies that have been conducted. Bohr 30 found no significant differences in self-concept between a group of children with physical disabilities and a control group of children without disabilities. Similarly, Magill and Hurlbut 15 found no overall differences between the self-concept of a group of adolescents with cerebral palsy and a matched control group of adolescents without physical disabilities. However, these researchers did find that girls with cerebral palsy had significantly lower self-concept. King et al 14 also reported that adolescents with chronic disabilities including cerebral palsy demonstrated no differences on global measures of self-concept and self-esteem, although these researchers did find significantly lower self-concept in the domain of athletic competence.
Our results and those in the previous literature suggest that clinicians should not assume that children with cerebral palsy have lowered self-concept or self-esteem. This also means that the relatively small reductions in the children’s self-concept may not be clinically significant and therefore the findings of this study do not suggest that clinicians and parents should be overly concerned with implementing strength-training programs for children with cerebral palsy. It is even possible that rather than being detrimental to the children, a physical program such as the one implemented in this study may provide children with an opportunity to develop a more realistic self-evaluation of their own skills and abilities, which in turn may provide these children with better preparation for adult life.
It needs to be acknowledged that a relatively small sample of children with diplegic cerebral palsy was selected as a sample of convenience from the gait laboratory of a metropolitan children’s hospital. Therefore, the ability to generalize our findings to the whole cerebral palsy population may be limited. In addition, the time frame over which changes in self-concept were measured was relatively short. Further research using a larger sample over a longer period of time is required to evaluate any longer term effects that progressive resistance strength training might have on the self-concept of children with cerebral palsy.
This study is the first randomized, controlled trial to examine the effect of a strength-training program on the self-concept of children with cerebral palsy. Unexpectedly, we found an inhibitory effect on the self-concept of these children compared with controls. Most importantly, self-concept in the experimental group remained positive after the intervention, suggesting that the observed psychological effects of strength training were not detrimental to this small group of children with cerebral palsy. It is uncertain whether these changes affect the self-concept of children with cerebral palsy in the longer term.
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