Physical activity measurement instruments for children with cerebral palsy: a systematic review

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1 DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY REVIEW Physical activity measurement instruments for children with cerebral palsy: a systematic review CATHERINE M CAPIO 1 CINDY H P SIT 1 BRUCE ABERNETHY 1 ESMERITA R ROTOR 2 1 Institute of Human Performance, The University of Hong Kong, Hong Kong. 2 College of Allied Medical Professions, University of the Philippines, Manila, the Philippines. Correspondence to Catherine M Capio, Institute of Human Performance, The University of Hong Kong, Pokfulam Road, Hong Kong. ccapio08@hku.hk PUBLICATION DATA Accepted for publication 2nd June Published online 14th July LIST OF ABBREVIATIONS ASKp Activities Scale for Kids Performance version CAPE PAC Children's Assessment of Participation and Enjoyment Preferences for Activities of Children PAQ-A Physical Activity Questionnaire Adolescents AIM This paper is a systematic review of physical activity measurement instruments for fieldbased studies involving children with cerebral palsy (CP). METHOD Database searches using PubMed Central, MEDLINE, CINAHL Plus, PsycINFO, EMBASE, Cochrane Library, and PEDro located 12 research papers, identifying seven instruments that met the inclusion criteria of (1) having been developed for children aged 0 to 18 years, (2) having been used to evaluate a physical activity dimension, and (3) having been used in a field-based study involving children with CP. The instruments reviewed were the Activities Scale for Kids Performance version (ASKp), the Canada Fitness Survey, the Children s Assessment of Participation and Enjoyment Preferences for Activities of Children (CAPE PAC), the Compendium of Physical Activities, the Physical Activity Questionnaire Adolescents (PAQ-A), StepWatch, and the Uptimer. Second-round searches yielded 11 more papers, providing reliability and validity evidence for the instruments. RESULTS The instruments measure physical activity frequency, mode, domain, and duration. Although most instruments demonstrated adequate reliability and validity, only the ASKp and CAPE PAC have established reliability and validity for children with physical disabilities; the Uptimer has established concurrent validity. No instrument measuring intensity in free-living has been validated or found reliable for children with CP. INTERPRETATION The findings suggest that further studies are needed to examine the methodological properties of physical activity measurement in children with CP. Combining subjective and objective instruments is recommended to achieve better understanding of physical activity participation. Cerebral palsy (CP) refers to a group of disorders that are caused by a disturbance in the developing brain and which manifest as problems of movement and posture. 1 Children with CP present with a variety of developmental difficulties, but the hallmark finding is a disorder in the development of gross motor function. 2 Interest in the physical activity levels of children with CP has been driven by the recent shift in focus of rehabilitation programmes from minimizing deficits to enhancing activity participation. 3 Although the benefits of participation are well documented in children and adolescents, 4 physical activity levels among children and adolescents with CP appear to be lower than those of their typically developing peers. 5 8 This discrepancy needs to be addressed as it may contribute to the development of secondary conditions such as chronic pain, fatigue, and osteoporosis 9 in the CP population. Physical activity measurement instruments have been developed for purposes of surveillance, intervention, or programme evaluation. 10 Several published reviews provide useful information on the reliability and accuracy of specific instruments among children and adolescents However, the literature on the measurement of physical activity of children with CP is relatively sparse, and review recommendations are mostly aimed at typically developing children. General methodological considerations in children may be inappropriate for studies in children with CP. The associated impairments, such as spasticity and dyskinesia, 1 mayleadtoatypicalphysicalactivity patterns, thus pointing to the need for validated measurement instruments in this specific population. Considering that CP involves a wide range of disabilities, the assessment of physical activity levels in this population would be of principal value in the design and implementation of health, therapy, and physical education programmes. 14,15 Valid and reliable measures of physical activity among children with disabilities such as CP are especially critical to estimate participation, monitor compliance with recommendations, and quantify dose response relationships between interventions and outcomes. 16 There are numerous parameters that may be used to quantify dimensions of physical activity. These dimensions include intensity, frequency, and duration, which together provide a measure of the total volume of physical activity. 17 Other dimensions include the mode and domain of physical activity behaviour. 18 Measurement methods for physical activity may 908 DOI: /j x ª The Authors. Journal compilation ª Mac Keith Press 2010

2 also be broadly classified as subjective or objective. Subjective methods include questionnaires, interviews, and activity diaries or logs. 17 These provide useful information on the context of physical activity behaviours and participants perceptions, 19 and they are often utilized in large population-based studies, focusing on the role of variables such as socioeconomic status, living area, and activity behaviours. 20 However, subjective methods for children have weaknesses that are related to issues of recall errors, misrepresentations, and biases such as social desirability. 12 Correlations between subjective measures of activity and other objective activity measures have been found to be less than satisfactory 21 and, consequently, objective techniques have often been recommended to better match the frequent and short bursts of children s physical activities and to accommodate children s limited ability for recall. 22 Objective methods in physical activity assessment involve the quantification of physiological or biomechanical parameters and the estimation of physical activity outcomes, such as instantaneous and daily physical activity energy expenditure. 17 Direct observation, heart rate monitoring, and accelerometry are some of the objective measures that are currently being used. 18 In contrast to subjective techniques, these approaches have been found to be unlikely to produce biased measures of physical activity intensity and volume. 19 Tools such as heart rate monitors and motion sensors have been used with increasing regularity and have been shown to provide reliable information on patterns of physical activity within a given day or over several days. 23 With the availability of varied measurement instruments, the choice of what instrument to use is a common question among researchers and practitioners in the field of physical activity. 18 The best instrument or combination of instruments to use to measure physical activity among children with CP has not been established comprehensively in previously published literature. Thus, the aims of this review were to (1) identify relevant physical activity measurement instruments for children with CP in field-based studies and (2) summarize and evaluate the methodological properties of the included instruments. In addition, this review also discusses the implementation of these instruments in the measurement of physical activity in children and adolescents with CP, as reported from relevant studies. This synthesis represents an important step towards establishing evidence-based recommendations for intervention programmes and studies that examine the physical activity levels of this particular group of children. METHOD Search strategy and inclusion criteria An electronic search of the following databases was carried out within the maximum time periods available in their archives: PubMed Central ( ), MEDLINE ( ), CI- NAHL Plus ( ), PsycINFO ( ), EMBASE ( ), Cochrane Library ( ), and PEDro ( ). The following terms were used: physical activity, cerebral palsy, children, measurement(s). The keywords were also matched to the Medical Subject Headings (MeSH) index and searched as keywords. We found 12 What this paper adds ASKp and CAPE PAC were found to be valid and reliable for children with physical disabilities. The Uptimer was found to be valid and reliable in children with CP. research papers that used measurement instruments which satisfied the following criteria: (1) the population for which the instrument was used included children aged 0 to 18 years; (2) the instrument evaluated at least one of the dimensions of physical activity (intensity, frequency, duration, mode, and domain); and (3) the instrument was used in a field-based study involving children with CP. Measurement instruments were excluded if they were used primarily to measure function-specific energy expenditure (i.e. walking, running) and gait parameters. Only studies published in English were included. The titles of the measurement instruments were then used individually as keywords for a second round of electronic search using the same databases. In this search, the following terms were also used in combination with the instrument titles: children, cerebral palsy, validity and reliability. Data extraction and quality assessment In the first round of electronic search, the measurement instruments were identified by using a data extraction form for each individual research articles. The data extraction form retrieved the following information: study objectives, study design, participant selection and characteristics, measurement tools description, findings, and conclusions. It was pilot tested by two independent reviewers (CMC and ERR) on three studies to ensure reliable data extraction and to identify any potential source of ambiguities. Data extraction was then independently performed by the two reviewers for each of the articles, and the retrieved information was found to be consistent. Once the data extraction was completed, the physical activity measurement instruments were identified, followed by the second round of electronic search. Research articles that provided evidence for reliability and validity of the identified measurement instruments were found and assessed. The validity and reliability of the identified measurement instruments were examined using criteria that were based on overall systematic review principles, 24,25 guidelines on physical activity assessment in children, 10,18 the Outcome Measures Form, 26 and other systematic reviews on similar topics Substantial progress in evidence-based practice has resulted in systems for evaluating the quality of randomized controlled trials such as CEBM (Centre for Evidence-based Medicine) and PEDro (Physiotherapy Evidence Database). However, in this review, quality assessment was based on overall systematic review criteria, as the standardization of measurement properties to represent quality criteria are still limited. 30 The criteria for assessing the methodological properties (reliability and validity) of the instruments were pilot tested by two raters (CMC and ERR) on three instruments. Interrater agreement wasfoundtoexceed98%. The descriptive information about each measurement instrument was identified and included the methods of use, dimensions of physical activity measurement, and target Review 909

3 population. The methodological properties of the instruments were examined in terms of reliability (interrater, intrarater, test retest, reproducibility), validity (content, construct, and criterion), and accuracy (for the objective instruments). For reliability coefficients, measures of 0.80 and above were considered excellent, 0.60 to 0.79 adequate, and less than 0.60 poor. 26 The validity or accuracy of an instrument was judged to be excellent when more than two well-designed studies supported the instrument, adequate when there were one or two well-designed studies, and poor when validity or accuracy studies were poorly completed or when one or two welldesigned studies did not support the instrument. 26 Two of the authors (CMC and ERR) independently reviewed the instruments, identified the descriptive information, and assessed the methodological properties. Overall, there was 95% agreement between the two reviewers on the reliability, validity, and accuracy of the instruments. Disagreement between the two reviewers was resolved by discussion. RESULTS Search results The initial database search identified a total of 559 papers. Review of their titles and abstracts indicated that 492 did not meet the inclusion criteria. Twelve of the 67 remaining research articles were able to satisfy the inclusion criteria (Fig. S1, published online). Upon completion of the data extraction forms, 12 papers were found to report on 10 fieldbased studies on the physical activity of children with CP. Seven physical activity measurement instruments were identified: Activities Scale for Kids Performance version (ASKp), 31 Canada Fitness Survey, 32 Children s Assessment of Participation and Enjoyment (CAPE) Preferences for Activity of Children (PAC), 33 Physical Activity Questionnaire Adolescents (PAQ-A), 34 a questionnaire based on the Compendium of Physical Activity, 35,36 the Uptimer, 37 and StepWatch. 38 The first five of these are subjective instruments; the last two are objective instruments. The second round of database searching, using the names of the instruments as keywords, identified 564 papers (Fig. S2, published online). Based on a review of the titles, abstracts, and methods, 12 papers were found to provide evidence of reliability and or validity of the selected physical activity measurement instruments, one of which was also found in the results of the first round of database searching. Table SI (published online) provides a summary of the reviewed physical activity instruments and the field-based studies that have used these instruments. Information is presented in terms of dimensions of physical activity measurement, sample size and recruitment, characteristics of participants, and outcomes. ASKp was used in two field-based studies among participants with CP. Bjornson et al. 39 utilized ASKp to compare the physical activity and health of a group of children with CP and an age- and sex-matched group of children without CP through purposive sampling. In this study, measures of function, such as the Childhood Health Questionnaire 40 and Youth Quality of Life, 41 were used concurrently. Their findings showed that activity performance predicted the physical, emotional, and behavioural health of children with CP. Another study that used ASKp was completed by Palisano et al. 42 and involved adolescents with CP. This study used a bigger sample, and the research methodology included a preliminary validation of ASKp among children with musculoskeletal limitations (including children with CP). The overall findings demonstrated that motor abilities of adolescents with CP influenced their physical activity participation. The CAPE 33 was used in four studies (five full-text papers), three of which recruited participants through purposive sampling 3,43 45 and the other through convenience sampling. 46 Generally, these studies demonstrated lower intensity of participation among participants with CP. The use of the CAPE among participants with CP in these studies also illustrates differences in methodological implementation. The study by Engel-Yeger et al. 43 involved adolescents who completed the instrument themselves. A preliminary check of the CAPE was achieved using test retest reliability. In the study by Majnemer et al., 3 the CAPE was administered with the assistance of the participants occupational therapists. Children who were not able to complete the questionnaires independently were also assisted by their parents in another study. 44,45 In yet another study that recruited both children and adolescents through convenience sampling, the CAPE was administered in the form of telephone interviews. 46 The implementation of the CAPE in children and adolescents with CP has been varied and tailored according to the needs of different participant groups. The Canada Fitness Survey 32 was used in a large population-based study by Longmuir and Bar-Or. 47 Before data collection, the survey was modified and checked for test retest reliability. This study was not limited to respondents with CP, but rather involved children and adolescents with any type of permanent disability. Another study used a modified questionnaire, 8 but this time based on the Compendium of Physical Activities. 35,36 There was no indication of any preliminary testing of this questionnaire. Responses were made by the parents of the participants rather than by the participants themselves. Another self-report instrument, namely the PAQ-A, 48 has been used with a sample of adolescents with CP. 6 Participants were recruited through purposive sampling and the data were compared with normative data from the literature. This study conducted preliminary test retest reliability and concurrent validity against pedometry, accelerometry, and logbook records before actual administration in the study. To date, two field-based studies have used objective instruments to measure physical activity in children with CP: Step- Watch was used by Bjornson et al., 5 and the Uptimer was used by Pirpiris and Graham. 15 These studies demonstrated that children with CP had lower physical activity levels than the norms of typically developing children. In the study that used the StepWatch, 5 the instrument was calibrated individually for each participant, and accuracy was checked against walking trial samples. Calibration accuracy of the instruments against manual counts of steps averaged 99.7% across the 910 Developmental Medicine & Child Neurology 2010, 52:

4 study sample. The aim of the study that used the Uptimer was primarily to examine the utility of the instrument in children with CP, and thus compared uptime measurements with the results of other standardized instruments, such as the Childhood Health Questionnaire 40 and the Functional Mobility Scale. 49 Physical activity dimension Physical activity measurement may include one or more of the dimensions of intensity, frequency, duration, mode, and domain. 17,18 The seven instruments that were reviewed each measured different physical activity dimensions (see Table SI); three measured a single dimension. ASKp examines the mode of physical activity (or the type of behaviour). Of the seven locomotion components of ASKp, one item enquires whether the respondent is able to walk (or wheel) in crowded areas, rough surfaces, and up a gentle hill. 31 Of the two play components, one item determines whether the child plays some sports alone or with a few friends. The response choices are on an ordinal scale, representing the length of time a child is able to carry out the play activities independently. The StepWatch and Uptimer are both objective instruments; they measure a single dimension each and provide continuous data. StepWatch measures physical activity intensity as it counts the number of steps over a given time interval, which, in turn, can be used to provide an estimate of energy expenditure. 38 It is worn on the ankle and may be used for long-term step monitoring. The data reflect both minuteby-minute variations in step activity and a cumulative measure of steps over a period of time. The Uptimer measures duration, recording the amount of time spent in an upright position. 37 Attached to the thigh, the Uptimer device responds to changes in position relative to gravity. Uptime is recorded when the user is in an upright position, whereas downtime is recorded when the user is seated or in a reclining position. It does not, however, provide an estimate of energy expenditure. Four instruments measure three physical activity dimensions each. The Canada Fitness Survey evaluated the physical activity and lifestyle characteristics of Canadians between the age of 10 and 69 years in The physical activity component of the questionnaire includes a list of physical activity behaviours (mode), and respondents describe their frequency of engagement in each mode in the last 12 months plus the average duration (in minutes) for each period of activity. CAPE measures five dimensions of participation in physical activity: diversity, intensity, with whom, where, and enjoyment. 33 PAC is a parallel measure of preference for activities. Participation is reported in different activities, one of which is classified as active physical activities, referring to physical activity. This has been used as a measure of physical activity mode, and CAPE scoring also reports the context of activity (domain) and frequency of participation from a period of 1 day to 4 months. PAQ-A measures the frequency, mode, and domain of activity, giving nominal and ordinal data. Twenty-two different physical activity behaviours are listed, and participants report the frequency of engagement in such activities within 1 week (7d) and within 1 day. 48 Questions also cover the frequency of physical activity participation during and after school. Finally, the Compendium of Physical Activity is a coding scheme that classifies physical activity by energy expenditure in kilocalories, thus giving estimates of intensity. 36 The coding scheme includes information on the major purpose of activities (domain), specific activities (mode), and intensity estimates. Questionnaires based on the compendium may then be able to capture these three physical activity domains. Reliability Table I shows the evidence in relation to different aspects of reliability for the subjective instruments. Evidence of internal consistency was found for three out of five subjective tools. ASKp and PAQ-A were found to have excellent internal consistency, with Cronbach s alpha exceeding 0.80, 31,51 54 whereas CAPE PAC for the section on activity types reached the acceptable level ( ). 33 Test retest reliability has been reported for four of the subjective instruments. Excellent reliability was demonstrated by the intraclass correlation coefficients (ICC) of ASKp, CAPE PAC, and PAQ-A, which exceeded ,33,51 However, the ICC reported for the Canada Fitness Survey did not reach the 0.60 standard, 55 indicating poor test retest reliability. Only ASKp and CAPE PAC have evidence of intrarater and interrater reliability. For both instruments, the ICC exceeded the excellent (0.80) level. 31,33 We could find no evidence for the reliability of the Compendium of Physical Activity. Evidence of reliability of the selected objective instruments is summarized in Table II; the Uptimer has been shown to have excellent test retest reliability, 15 with an ICC exceeding The reliability evidence found for StepWatch refers to reproducibility which found low levels of error (SEM 3, SD 1) when comparing measurements taken from the right and left legs of each participant. 56 Validity and accuracy Table III summarizes the evidence regarding the validity of the subjective measurement instruments. The available evidence indicates that ASKp has excellent content validity. 31,53,54 CAPE PAC appears to have adequate content validity based on one study reported in its manual. 33 PAQ-A was a modification of another version for older children. We found no study that directly examined the content validity of PAQ-A; however, evidence from validity studies shows that the version for older children has adequate concurrent validity with other measures of physical activity. 51 Convergent and discriminant validity were found to be adequate in ASKp, 53 PAQ-A, 52 and CAPE PAC. 58 Adequate evidence was reported for the concurrent validity of ASKp 53 and PAQ-A. 52 There is no direct evidence available to assess the different aspects of validity for the Canada Fitness Survey and the Compendium of Physical Activities. Evidence of validity of the objective instruments is summarized in Table IV. StepWatch was shown to have excellent Review 911

5 Interrater reliability Intrarater reliability Test retest reliability Internal consistency (Cronbach s alpha) Child parent: ICC: 0.97 Child: 0.97; parent: 0.94 NA NA NA ICC: 0.53, weighted kappa: ICC: NA Interviewer client: NA NA NA Generalizability coefficient: NA NA 0.88 Generalizability coefficient: NA step-counting accuracy for children. 56,57 Convergent and discriminant validity were also found to be adequate for StepWatch, and defined step activity rates were found to reflect the linear increments in children s activities. Adequate evidence was also reported for the concurrent validity of StepWatch 57 and the Uptimer. 15 The concurrent validity evidence supporting the Uptimer included evidence from studies in children with CP, whereas the evidence for Step- Watch was limited to typically developing children. DISCUSSION This review focused on field-based studies, with the aim of measuring physical activity levels of children with CP in freeliving conditions. This approach is consistent with the World Health Organization International Classification of Functioning, Disability and Health. 59 This model views health, function, and disability as an interaction of biological, individual, and social factors. It has been widely used to guide clinical thinking and service delivery for children and adolescents with CP, 60 and has been found to provide an applicable framework for interventions that seek to enhance the activity and participation of children with physical impairments. 61 As such, the quantification of activity performance among children with CP needs to be reflective of their daily life experiences within the environment in which they live. 5 Furthermore, we deem this important because physical activity in children with disabilities is often promoted through adapted physical education. 14 Table I: Reliability data for selected subjective physical activity measurement instruments Instrument Study Participants Young 31 and Children with activity limitations Young et al. 53,54 associated with musculoskeletal conditions, mean age 11y 7mo (SD 3y 1mo; n=28). Parents of the participating children Activities Scale for Kids Performance version (ASKp) Canada Fitness Survey Weller and Corey 55 Adolescents and adults without disabilities, aged 15 80y (n=127; 64 males, 63 females) King et al. 33,58 Children with physical function limitations, aged 6 12y (n=427; 229 males, 198 females) Children s Assessment of Participation and Enjoyment (CAPE) Crocker et al. 51 and Adolescents without disabilities, aged Janz et al y (n=97) Children without disabilities: mean age Physical Activity Questionnaire for Adolescents (PAQ-A) 11y 4mo (SD 4mo; n=210; 104 males, 106 females) NA, not applicable; ICC, intraclass correlation coefficient. Methodological properties of instruments Currently, the most common methods used for assessment of physical activity in research are self-report instruments and movement sensors. 17 Identifying which instruments to use for specific groups of participants can be rather challenging 18 because established evidence has been mostly derived from studies of typically developing populations. In this systematic review, we found seven instruments that have been used in studies which examined variables that included physical activity among children with CP. Evidence supports adequate to excellent overall reliability and validity of most of the instruments. However, studies that support the methodological properties of these instruments for the particular group of children with CP were found to be limited. The ASKp and CAPE PAC are supported by published studies that examined the reliability and validity of the instruments in samples that included children with physical disabilities. Studies have used these instruments to compare physical activity dimensions among children with CP and those who are developing typically. 39,43 Of the two objective instruments, established evidence for criterion validity among children with CP is available only for the Uptimer. 15 The unique characteristics of the population being measured are important considerations in instrument selection. 62 This systematic review found that few true validated measures of physical activity in children with physical disabilities are available. 61 Those instruments that do have established methodological properties for field-based assessment of physical 912 Developmental Medicine & Child Neurology 2010, 52:

6 Table II: Reliability data for selected objective physical activity measurement instruments Instrument Study Participants Reproducibility Test retest reliability StepWatch Mitre et al. 56 Children without disabilities: mean age 11y (SD 1y; n=27; 13 males, 14 females) Uptimer Pirpiris and Graham 15 Children with CP: mean age 11y (SD 3y 11mo; n=300; 149 males, 151 females) SEM 3, SD 1 (compared measures of left right legs) NA NA ICC: SEM, standard error of the mean; NA, not applicable; ICC, intraclass correlation coefficient. activity among children with disabilities do not seem to be adequate to address purposes of research, surveillance, and monitoring in children with CP. Daily physical activity has been described as complex and multidimensional, 63 resulting in the absence of a single assessment tool that will capture and describe physical activity dimensions. 18 In our review, three instruments have evidence supporting some methodological properties when used among children with CP: ASKp, CAPE PAC, and the Uptimer. Physical activity dimensions that are measured by these three instruments include frequency, mode, domain, and duration. No instrument that measures intensity in free-living conditions has been validated nor found reliable for children with CP. Application in children with CP It has been noted in previous reviews of physical activity measurement in the general population that subjective and objective instruments have clearly different purposes, and thus have different implementation considerations as well. The subjective instruments reviewed in this paper are all self-reports, which implies that their applicability among participants with CP may be influenced by their cognitive abilities. For these five instruments, the implementation methods allow for assistance to be provided by parents and teachers in completing the reports, indicating that these instruments may be used across different levels of cognitive abilities in children with CP. This was, in fact, apparent in some of the field studies that used these instruments in children with CP. The ASKp was completed with the assistance of parents, 39,42 and participants whorespondedtothecape PAQ were assisted by their parents 45,46 or therapists. 3 The questionnaires based on the Compendium of Physical Activities were actually filled out by the parents of the participating adolescents with CP; 8 the PAQ-A was also implemented with the assistance of parents or guardians of adolescents with CP. 6 However, previous reviews of physical activity measurement among typically developing children have pointed out that subjective instruments have limitations associated with bias and recall errors. 12 Furthermore, recommendations indicated that objective measures are better suited to the nature of activities that children engage in. 22 It is indeed desirable that future research on children with CP utilizes objective physical activity measurement instruments. However, in this review, we found only two objective instruments that have been used in field-based studies of children with CP. Although both instruments have been found to have adequate to excellent validity and reliability in typically developing children, only the Uptimer has evidence supporting its methodological properties for useinchildrenwithcpinparticular.asnotedearlier,the Uptimer measures only the duration in the upright position, and does not provide an estimate of energy expenditure. The lack of valid and reliable objective measurement instruments for other physical activity dimensions (such as intensity, mode, and frequency) among children with CP implies that further research needs to be carried out to establish adequate methods of objective physical activity monitoring in this group of children. The instrumentations of the reviewed objective measures are both associated with independent ambulation and mobility. As such, utility in children with CP may be limited by the participants motor abilities. It appears that both the Uptimer and StepWatch may be used only by participants classified in Gross Motor Function Classification System levels I to III, who are able to walk independently with or without assistive devices. Nevertheless, the use of the two objective instruments appears to be feasible among children with CP. The use of StepWatch was reported to elicit high compliance 57 and was well tolerated by typically developing children and adolescents. 56,64 When it was used among children with CP, no adverse effects or reports of discomfort were noted. 5 Similarly, the use of the Uptimer in children with CP did not cause any irritation or disturbance among the participants. 15 Limitations This systematic review was able to identify evidence for the methodological quality of the reviewed physical activity measurement instruments, but these did not encompass all aspects of validity and reliability. Furthermore, validation and reliability studies that particularly examine children with CP are limited. Thus, this review presents measurement instruments that were used in field-based studies of children with CP, but the validation and reliability studies supporting these instruments were mostly carried out among typically developing children. Recommendations for research Valid and reliable physical activity assessment instruments are critical for understanding participation, compliance, and intervention effects. 16 In particular, accurate and reliable physical Review 913

7 Table III: Validity data for selected subjective physical activity measurement instruments Instrument Study Participants Content validity Convergent divergent validity Discriminant validity Concurrent validity Activities Scale for Kids Performance version (ASKp) Children s Assessment of Participation and Enjoyment (CAPE) Physical Activity Questionnaire for Adolescents (PAQ-A) Young 31 and Children with activity Young et al. 53,54 limitations associated with musculoskeletal conditions: mean age 10y 1mo (SD 3y 1mo; n=200; 10 males, 100 females) King et al. 33,58 Children with physical function limitations, aged 6 12y (n=427; 229 males, 198 females) Kowalski et al. 34 and Adolescents without Janz et al. 52 disabilities: mean age 16y 3mo (SD 1y 6mo; n=85; 41 males, 44 females) Children without disabilities: mean age 11y 4mo (SD 4mo) (n=210; 104 males, 106 females) Comprehensive literature review. Structured interviews of children (n=20) and parents. Review by a panel of experts (n=7) in child life, epidemiology, home care nursing, occupational and physical therapy, and orthopaedic surgery. Field testing among children with disabilities (n=28) Comprehensive literature review. Review by a panel of experts. Pilot testing in children with and without disabilities Convergent and divergent validity compared with subscales of the Health Utility Index 66 (convergent R=0.43, divergent R=)0.03) Convergent validity compared with environmental, family, and child variables (R= ) NA Convergent validity compared with other physical activity measures (R= ) Ability to detect gradations of disability compared with Child Health Assessment Questionnaire 40 (R=0.81) Discriminant validity compared with environmental, family, and child variables (R= ) NA NA Comparison of clinicianreported ASKp scores with clinician s global ratings (R=0.92) Comparison with Self- Perception Profile for Children 67 and Self- Perception Profile for Adolescents 68 (R= ) NA NA NA Comparison with data from activity monitors for total physical activity (R=0.56) and MVPA (R=0.63) NA, not applicable. MVPA, moderate-to-vigorous physical activity. 914 Developmental Medicine & Child Neurology 2010, 52:

8 Table IV: Validity data for selected objective physical activity measurement instruments Instrument Study Participants Accuracy Convergent divergent validity Concurrent validity StepWatch McDonald et al. 57 Children and Activity Monitor adolescents aged 6 20y (n=83; 41 males, 42 females) Uptimer Mitre et al. 56 Pirpiris and Graham 15 Children: mean age 11y (SD 1y; n=27; 13 males, 14 females) Children with CP: mean age 11y SD 3y 11mo (n=300; 149 males, 151 females) SEM, standard error of the mean; NA, not applicable. Step counting accuracy in continuous step activity in children (99.87%) Step counting accuracy in treadmill and freewalking in children (SEM 5, SD 0.6) Divergent validity of Comparison with heart rate defined step activity rate monitoring (R=0.49) showing linear increments in children (p<0.05) NA Comparison of steps counted with walking energy expenditure measures (R 2 =0.86) NA NA Comparison with functional measures in children with CP 68 (R= ). Comparison with direct observations in children with CP (R=0.98) activity assessment is necessary for any further investigations where physical activity is either an outcome or an intervention. 22 There is a need for further research to establish evidence for the use of both subjective and objective instruments in field-based studies of physical activity in children with CP. The instruments we reviewed have also been used in other groups of children with physical impairments, 65 which highlights the need for further studies on the reliability and validity of physical activity measurement instruments in population groups of children with disabilities. Ultimately, there is no one assessment instrument that can quantify all the dimensions of physical activity. A researcher s choice of instruments should be closely aligned with rigorously defined intents of a study. 18 For purposes of investigating the physical activity levels of children with CP in free-living conditions, a combination of subjective and objective instruments is recommended to gain a better understanding of physical activity participation. This review suggests that the instruments may need to be combined for such studies and will require further verifications of validity and reliability for this particular group of children. ONLINE MATERIAL Additional material and supporting information may be found in the online version of this article. REFERENCES 1. Rosenbaum P, Paneth N, Leviton A, et al. A report: the definition and classification of cerebral palsy, April Dev Med Child Neurol 2007; 49(Suppl. 109): Rosenbaum PL, Walter SD, Hanna SE, et al. Prognosis for gross motor function in cerebral palsy: creation of motor development curves. 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