Developmental Neurorehabilitation, October 2008; 11(4): 276–282

Association between motor and mental functioning in toddlers with

cerebral palsy

LOTTE ENKELAAR1,2, MARJOLIJN KETELAAR1,2,3, & JAN WILLEM GORTER2,4

1Rehabilitation Centre De Hoogstraat, Centre of Excellence for Rehabilitation Medicine, Utrecht, The Netherlands,2Partner of NetChild, Network for Childhood Disability Research in the Netherlands, Utrecht, The Netherlands,3Department of Rehabilitation and Sports Medicine, Rudolf Magnus Institute of Neuroscience, University Medical

Center, Utrecht, The Netherlands, and 4CanChild Centre for Childhood Disability Research, McMaster University,

Hamilton, ON, Canada

(Received 18 August 2008; revised 21 October 2008; accepted 27 October 2008)

AbstractPurpose: This study aimed to examine the association between motor and mental functioning in toddlers with cerebralpalsy (CP).Methods: The Mental and Motor Scales of the Bayley Scales of Infant Development–Second Edition (BSID-II) wereadministered.Subjects: Seventy-eight toddlers with CP (mean age 2 years 7 months, SD 1 month; 43 boys, Gross Motor FunctionClassification System (GMFCS) levels I–V).Results: Spearman correlation coefficient between mental and motor functioning was 0.67 (p < 0.01). Sixty-five percent (51/78) of the children performed at the same level in mental and motor functioning, of whom 36 performed significantlydelayed and 15 within normal limits. Thirty-five percent of the children were more delayed in motor functioning than inmental functioning.Conclusion: In toddlers with CP, an association was found between mental and motor functioning. When motor and mentalfunctioning did not develop synchronously, it was always in favour of mental functioning. This study emphasizes theimportance of examining both mental functioning and motor functioning separately of pre-school children with CP.

Keywords: Cerebral palsy, children, motor, mental, functioning

Introduction

Cerebral Palsy (CP) is a complex neurodevelop-mental condition. According to a recently publisheddefinition, CP describes a group of permanentdisorders of the development of movement andposture, causing activity limitations, which areattributed to non-progressive disturbances thatoccurred in the developing foetal or infant brain[1]. The motor disorders of CP are often accom-panied by disturbances of sensation, perception,cognition, communication and behaviour, by epi-lepsy and secondary musculoskeletal problems [1].Moreover, there is a wide spectrum in the severity ofimpairments and activity limitations.

Literature on children with CP still emphasizes themotor impairment. Recent studies, however,demonstrated that apart from the movement dis-order, there are other important factors influencingevery day functioning of children with CP

significantly. These are: anatomical distribution,epilepsy and learning disabilities [2–5]. Learningdisabilities are rather common in children with CP.According to the findings of the Surveillance ofCerebral Palsy in Europe (SCPE) study group 31%of the children with CP have an IQ less than 50 [6].Beckung and Hagberg found that 40% of childrenwith CP had learning disabilities, of which 14% hadmild (IQ 50–70) and 26% had severe (IQ < 50)cognitive impairments [2].

In the Netherlands, young children with develop-mental disabilities often go to specialized toddlergroups (2–4 years of age) in rehabilitation centres, inwhich the groups are often formed according to thedevelopmental needs of the children. At the age of4 years most of the children go to a primary school:mainstream schools or schools for special education.In both phases, the developmental level of thechildren is regarded to be very important to inform

Correspondence: M. Ketelaar, Rehabilitation Centre De Hoogstraat, Centre of Excellence for Rehabilitation Medicine, Rembrandtkade 10, 3583 TM Utrecht,The Netherlands. Tel: 3130-2561211. Fax: 3130-2511344. E-mail: M.Ketelaar@dehoogstraat.nl

ISSN 1751–8423 print/ISSN 1751–8431 online/08/040276–7 � 2008 Informa UK Ltd.DOI: 10.1080/17518420802581164

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parents and for the placement of the individual childin the most appropriate group or school. There areno uniform guidelines how to assess the develop-mental level of children with CP at this age.Sometimes the decisions are based on the motorfunctioning of the child and sometimes standardizedassessments such as the Bayley Scales of InfantDevelopment-Second Edition (BSID-II) are used.When relying solely on the level of motor functioningit should be clear what the association betweenmotor and mental functioning is. Although learningdisabilities are frequently occurring impairments,with a significant influence on everyday functioning,there is little information on the direct associationbetween the development in motor functioning andmental functioning. Vohr et al. [7] found that thepercentage of low scores on the Mental Scale of theBSID-II increased linearly with the severity of motorproblems (as measured by the number of limbsinvolved), with the exception of the children withhemiplegia, who tended to have higher scores thanthe children with monoplegia [7]. Russman et al. [8]also reported that there is in general some, but noabsolute, relation between the number of limbsinvolved and severity of mental impairments.However, limb involvement might not be the mostreliable and best indicator of motor functioning ofthe child with CP [9].

The SCPE published guidelines for the systematicclassification of children with CP. According to theguidelines children with CP can be classifiedaccording to their predominant motor disorder,i.e. the spastic, dyskinetic and ataxic subtypes. Thespastic [10] subtype is further divided into aunilateral and a bilateral involvement. Severity ofgross motor problems can be classified reliably bymeans of the Gross Motor Function ClassificationSystem (GMFCS) [11,12].

The purpose of the present article is to examinethe relation between the mental and motordevelopment index of the BSID-II, in toddlers withCP; and to explore if the type of CP, anatomicaldistribution (unilateral and bilateral involvement)and GMFCS-level are related to the mental andmotor development index.

Methods

The present study is part of the PERRIN CP 0–5study which, in turn, is part of a longitudinalresearch program entitled Paediatric RehabilitationResearch in the Netherlands (PERRIN). In thePERRIN program, the course and determinants offunctional status of children and adolescents withCP are studied. The International Classification ofFunctioning, Disability and Health [13] has been

used as a conceptual framework for PERRIN, witha primary focus on Activities and Participation(www.perrin.nl). The focus in PERRIN CP 0–5 ison the development of young children with CPstarting at the age of 18 months.

Participants

For the purpose of the present study, we cross-sectionally examined toddlers, i.e. children at the ageof 30 months. At 30 months the diagnosis of CPusually has been established and children are oftenreferred to a paediatric rehabilitation centre fortreatment.

Children who were assessed with both the Mentaland Motor Scale of the BSID-II, as part of thePERRIN CP 0–5 study, were included in the presentstudy. Because 22 children in the PERRIN CP 0–5study had no complete BSID-II, the data of 78children, aged 2.5 years and all diagnosed with CP,fulfilled the criteria for the present study. Thechildren with complete BSID-II data did not differfrom the children with incomplete data with respectto severity, measured by the GMFCS level (�2

¼ 2.7,p¼ 0.62). The data were collected during one or twomorning sessions by trained research assistants andresearchers.

Parents were asked by their treating paediatrician,child neurologist or rehabilitation physician whetherthey were willing to participate in the PERRIN CP0–5 study. Cases in which the child was diagnosedwith other diseases affecting motor functioning or inwhich the parents faced problems with the Dutchlanguage were excluded. Informed consent wasgiven by the parents of 100 children. Ethicalapproval for the study was given by the Committeefor Medical Ethics of the University Medical CentreUtrecht. The children were measured in participat-ing rehabilitation centres and university hospitalsthroughout the Netherlands (Acknowledgements).

Measures

To measure mental and motor functioning, theDutch translation of the BSID-II Mental andMotor Scales [14,15] were administered by trainedresearchers. The BSID-II is an individually adminis-tered examination, which assesses the current devel-opmental functioning of infants and children aged1–42 months. The BSID-II consists of three scales:The Mental Scale, the Motor Scale and BehaviourRating Scale [14], of which the latter was not used inthe present study. The Mental Scale assesses thechild’s current level of cognitive, language andpersonal-social development. This includes itemsthat assess memory, habituation, problem solving,early number concepts, generalization, classification,vocalizations, language and social skills. The Motor

Association between motor and mental functioning 277

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Scale measures fine and gross motor development.This includes the movements associated with rolling,crawling and creeping, sitting, standing, walking,running and jumping as well as the fine motormanipulations involved in writing and imitation ofhand movements. The scores on the Mental andMotor scales can be converted into a normalizedstandard score, namely, the Mental DevelopmentIndex (MDI) and the Psychomotor DevelopmentIndex (PDI). MDI and PDI scores of 100 (SD¼15)represent the mean. The children’s MDI and PDIscores can be categorized into ‘significantly delayed’(<69); ‘mildly delayed’ (70–84); ‘within normallimits’ (85–114) and ‘accelerated performance’(>115), based on reference data provided in theAmerican manual [14]. The American BSID-II hasshown to be reliable and valid for children withoutdisabilities [14]. Usage of the first edition of theBSID for children with CP was studied by Harriset al. [16]. It was found that the children with CP hadsignificantly lower scores on the Mental Scalecompared to peers. Furthermore, they discoveredthat the BSID Motor Scale was extremely sensitive inpicking up motor deficits in children with CP [16].

The subtypes of CP, by type of motor disorder(spastic, ataxia or dyskinetic) and topographicaldistribution for spastic CP (unilateral or bilateral),were classified according to the SCPE guidelines[1,6,10]. To classify the severity in functional motorabilities, the Dutch translation of the GMFCS[11,17] was used.

The GMFCS is a five-level, ordinal, gradingwhich was developed to provide an objectiveclassification for children with CP based on abilitiesand limitations in gross motor function [11,17].Distinction between the different levels, rangingfrom level I (least limitations) to level V, are basedon functional abilities and the need for assistivetechnology, including mobility devices and wheeledmobility rather than quality of movement. Since theclassification of motor function depends on age, forthis study we used the descriptions provided forchildren 2–4 years, which is included in theAppendix [11]. The GMFCS has shown goodvalidity and reliability for children 2 years andabove [18,19].

Statistical analysis

Statistical analyses were performed with SPSS soft-ware (version 14.0). Because the data for the PDIand MDI were not normally distributed, non-parametric statistics were used. To examine theassociation between the motor and mental function-ing, Spearman correlations between the normalizedstandard scores MDI and PDI were computed.Correlations were considered significant for p-values

<0.05. To examine the relation between anatomicaldistribution and MDI and PDI, the Mann–WhitneyU-test was performed, and for the relation betweenGMFCS and MDI and PDI, Spearman correlationswere calculated. To determine differences in sub-types of CP between the different association groupsof motor and mental functioning �2-tests were usedfor the typology and the distribution of the CP andthe Mann–Whitney U-test was used for GMFCS.

Results

The characteristics of all children (N¼ 78, mean age2 years and 7 months, SD 1 month) are presentedin Table I. Seventy-five children were classified ashaving a spastic type of CP, of whom 34 hadunilateral and 41 bilateral involvement. Threechildren had a dyskinetic type and no children inthis study group had an ataxic type of CP. GMFCSlevels ranged from I to V.

For the Mental Scale of the BSID-II, 36 childrenwere significantly delayed, 7 were delayed and 35children were functioning within normal limits.On the Motor Scale 58 children were significantlydelayed, 5 delayed and 15 were within normal limits.No children demonstrated accelerated performanceon either the Mental or Motor Scale.

The association between the MDI and PDI scoresin toddlers with CP was 0.67 (Spearman’s rho, withp < 0.01). When examining the relation between typeof CP and the mental and motor development index,it was clear that because of the limited number ofchildren in the dyskinetic group, no significant

Table I. Characteristics of the participants.

Characteristic N (%)Mean (SD)

(range)

GenderMale 43 (55)Female 35 (45)

Age (in months) 31 (1) (28–34)

Typology of CPSpastic 75 (96)

Anatomic distribution Unilateral 34 (55)Bilateral 41 (45)

Ataxic 0 (0)Dyskinetic 3 (4)

GMFCSI 24 (31)II 9 (11)III 20 (26)IV 17 (22)V 8 (10)

Total 78 (100)

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conclusions could be drawn at the level of type ofCP. However, within the spastic group, the influenceof the anatomical distribution of the spastic childrenon the MDI score was significant (Mann–WhitneyU, Z¼�4.05, p < 0.05). Unilateral children hadhigher scores on the MDI than bilaterally affectedchildren and also more unilaterally than bilaterally-affected children performed within normal limits.The Spearman correlation between GMFCS andMDI was –0.73 (p < 0.01). Children with GMFCSlevel I had higher scores on the MDI than childrenwith GMFCS level V. For the Motor Scales thesame pattern of relations were found; a significantdifference between children with unilateralspastic CP and children with bilateral involvement(Mann–Whitney U, Z¼�4.58, p < 0,05), in favourof the unilateral affected children. The Spearmancorrelation between GMFCS and PDI was �0.71(p < 0.01), with the level I having higher scores thanlevel V.

For ease of interpretation, the cross tab in Table IIdemonstrates the association between the classifica-tion categories of the MDI and PDI scores. Two-thirds of the children (51 of 78) performed at thesame level in mental and motor functioning(Group I), of whom 15 performed within normallimits in both mental and motor functioning (GroupIa) and 36 were significantly delayed in mental andmotor functioning (Group Ib). Twenty-seven chil-dren (35%) were more delayed in motor functioningthan in mental functioning (Group II). Of these27 children, 15 performed within normal limits inmental functioning and significantly delayed inmotor functioning. No children performed betterin motor than in mental functioning.

The subtypes of CP, i.e. type of motor disorder,anatomical distribution and severity, which might beimportant in the association between mental andmotor functioning, are displayed for the two groups(I and II) in Table III.

Overall, little difference is seen between themental-equals-motor group (Group I) and thegroup in which children performed better on

mental functioning than motor functioning (GroupII). No statistically significant differences betweenthe two main groups were found for anatomicaldistribution (�2

¼ 0.35, p > 0.05) and GMFCS(Mann–Whitney U, Z¼�1.48, p > 0.05).

Discussion

In young children with CP, a moderate associationwas found between mental and motor functioning,as measured by the BSID-II. In almost two-thirds ofthe toddlers, motor and mental functioning seemedto be developing synchronously. In those cases inwhich motor and mental functioning did not developsimilarly, it was always in favour of mental function-ing. The finding that scores on the Mental Scale ofthe BSID-II were higher than on the Motor Scale ofthe BSID-II in children with CP was also noticed,but not further investigated by Vohr et al. [7]. When

Table II. Cross tabulation of classification by mental functioning (MDI) versus motor functioning (PDI).

Classification PDI

ClassificationMDI

Significantly delayedperformance

Mildly delayedperformance

Within normallimits Total

Significantly delayed performance 36Ib 0 0 36Mildly delayed performance 7II 0 0 7Within normal limits 15II 5II 15Ia 35

Total 58 5 15 78

Note: Group I: Mental functioning¼Motor functioning. Group Ia: Both within normal limits. Group Ib: Both significantlydelayed. Group II: Mental functioning > Motor functioning.

Table III. Association between mental and motor functioningclassified by typology, anatomical distribution and GMFCS (innumber N and percentage of columns).

Characteristic

Group I: Mentalfunctioning¼Motor

functioning N

(% of columns)

Group II: Mentalfunctioning >

Motor functioningN (% of columns)

Typology of CPSpastic 49 (96.1) 26 (96.3)Dyskinetic 2 (3.9) 1 (3.7)Total 51 (100) 27 (100)

Anatomical distribution of children with spastic CPUnilateral 21 (42.9) 13 (50)Bilateral 28 (57.1) 13 (50)Total 49 (100) 26 (100)

GMFCSI 17 (33.3) 7 (25.9)II 2 (3.9) 7 (25.9)III 11 (21.6) 9 (33.3)IV 13 (25.5) 4 (14.8)V 8 (15.7) 0 (0)

Total 51 (100) 27 (100)

Association between motor and mental functioning 279

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comparing the characteristics (anatomical distribu-tion and GMFCS) of the children in the group inwhich motor and mental functioning was developingin the same way (Group I) with the children in thegroup in which this was not the case (Group II), nosignificant differences were found.

When looking at the influence of differentcharacteristics of CP on the performance on theMental and Motor Scale separately, our results showthat anatomical distribution (unilateral vs. bilateralinvolvement) and severity of gross motor problemsby GMFCS levels were related to the Mental andMotor Index of the BSID-II. The children withbilateral CP had significantly lower scores on theMental and Motor Scales, than the children who hadunilateral CP. The fact that significantly moreunilaterally- than bilaterally-impaired children per-formed within normal limits on both Motor andMental Scales of the BSID-II, is in agreement withfindings by Vohr et al. [7]. They also found that thenumber of children with low scores on the Motorand Mental Scale of the BSID-II increased with thenumbers of limbs involved except for the childrenwith hemiplegia [7]. In our study we limitedourselves to the major categories of unilateral andbilateral involvement in children with a spasticsubtype, a classification of which we can trust it tobe reliable. Taking the study by Vohr et al. [7] andour study together, we can conclude that anatomicaldistribution in two main categories is a reliable andvalid variable that is related to both the level ofmental and motor functioning.

Our results further showed a significant negativeassociation between GMFCS level and mental andmotor functioning. Children with GMFCS level Ihad higher scores on the Mental and Motor Scales ofthe BSID-II than children with GMFCS level VGorter et al. [9] found significant, but low associa-tions between type of CP, limb distribution andmotor ability described by using the GMFCS. Ourresults show–in a different way–relationshipsbetween limb distribution and motor ability on onehand and motor and mental functioning as measuredby the BSID-II on the other hand. In previousstudies [3,5], the GMFCS was a good predictor ofeveryday functioning with age and learning problemsas significantly contributing factors. To fully under-stand the relationships between type of CP, limbdistribution, motor ability and motor and mentalfunctioning, and how these relations evolve overtime, longitudinal research is required.

Although anatomical distribution and GMFCSlevel were related to the scores on the Mental andMotor Scale of the BSID-II, they were not thedifferentiating factors for the synchronically andnon-synchronically developing group in mental andmotor functioning. Because the GMFCS was

developed a classification system for gross motorfunction, it does not tell to what extent the manualabilities might play a role in the assessment of motorand mental functioning by means of the BSID-II.Therefore, it would be interesting to determine therelationship between the fine motor function andBSID-II Mental and Motor Scale scores. This isespecially interesting because a common criticism onthe BSID-II Mental Scale is that children need tohave good fine motor function to perform on theitems of the BSID-II [16]. In other words, whena child with severe limitations in fine motorfunctioning is assessed with the BSID-II on mentalor motor functioning, this could lead to an under-estimation of development. Beckung and Hagberg[2] found that, in addition to gross motor function,IQ and bimanual fine motor function were impor-tant predictors of participation restrictions, makingfurther research into the relationships between finemotor function and mental and motor functioningeven more important. Moreover, other internal andexternal factors, such as epilepsy, communicationproblems or family related factors, also might haveinfluenced the relationship between mental andmotor functioning, and need to be furtherinvestigated.

Taken the limitations into account, our resultsmake clear that even with significantly delayed motorfunctioning, a child can have a mental functioningwithin normal limits. This is an important findingbecause of the importance of knowledge of thedevelopmental level of young children to informparents and for the placement of the individual childin the most appropriate group or school. It meansthat an indication of mental functioning cannot bebased solely on motor functioning.

With regard to the generalizability of our results itneeds to be said that this was a clinical-based study,and therefore not representative for the total ofchildren with CP in the Dutch population. Becausethe characteristics of the participants are rathersimilar to other hospital-based studies [20,21], ourresults are more likely to represent the children withCP known in rehabilitation centres and hospitals.

In the present study, only 3 of 78 children hada dyskinetic type of CP (3.7%), a bit less than the6.5% found by the SCPE [6]. But, in accordancewith the SCPE [6], the majority of the children hadthe spastic subtype of CP. Because of the smallnumber of children with the dyskinetic type and theabsence of the ataxic type of motor disorder in thisstudy, it was impossible to study the relationshipbetween type of motor disorder of CP and mentaland motor functioning. Of the three children withthe dyskinetic type of motor disorder, two weresignificantly delayed and one was within normallimits for mental functioning, and all were

280 L. Enkelaar et al.

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significantly delayed in motor functioning. So evenin this small group, there was diversity within thisparticular subtype. Further research concentrated onthis particular type of motor disorder is necessary toreveal more clarity.

Assessment of young children can be challengingand separation between different aspects of devel-opment is not easy. But our results show that eventhough the mental and motor functioning of childrenwith CP are closely related, there are also children inwhom motor and mental functioning did notdevelop in the same way. In these cases, it wasalways in favour of mental functioning. The impactof this finding could be substantial. First, profes-sionals need to take into account that if a child issignificantly delayed in motor functioning, he or sheis not automatically mentally impaired and canperform mentally in an age appropriate way.Second, it is not clear how the association betweenmental and motor functioning evolves over timeand what factors influence this association. Earlierfindings of Cole and Harris indicated that thecognitive-motor relationship in young childrenenrolled in a special education program changedsubstantially between yearly assessments [22].Third, the findings of the present study also meanthat developmental programs or education forchildren with CP must be able to differentiatelevels of mental and motor development.Furthermore, if our results can be replicated andreaffirmed that when motor and mental develop-ment differ, this is always in favour of mentaldevelopment, this could lead to interesting hypoth-eses. If motor development in most cases of non-synchronous motor and mental development lagsbehind mental development, perhaps mental devel-opment is a limiting factor for motor development. Ifso, it might be that stimulating mental developmentwould have a greater impact on motor progress thanstimulating motor functions alone. To gain moreinsight into these processes, it would be necessary toexamine if these relationships, between mental andmotor functioning, remain the same as the childgrows older. Longitudinal studies, in which childrenare followed for a number of years, could providemore insight into these questions.

Although overall a moderate association wasfound between mental and motor functioning intoddlers with CP, in one out of three children motorand mental functioning did not develop in the sameway. Children with severe CP and bilateral involve-ment are at risk for both delayed motor and mentalfunctioning. However, a significant delayed in motorfunctioning does not automatically imply animpaired mental development. Professionals alwaysneed to take this into consideration and testing of

both motor and cognitive functioning isrecommended.

Acknowledgements

This research has been performed as part of thePERRIN (Pediatric Rehabilitation Research in theNetherlands) research program, which has beensupported by the Netherlands Organisation forHealth Research and Development (grant number1435.0011). We would like to thank all children andtheir parents who participated in the PERRIN CP0–5 study. We also would like to express ourgratitude to the professionals who administered theBSID-II and to the rehabilitation centres anduniversity hospitals throughout the Netherlandsthat participated in the study: Rehabilitation CentreDe Hoogstraat, Utrecht; VU, University MedicalCentre, Amsterdam; Academic Medical Centre,Amsterdam; Erasmus Medical Centre, Rotterdam;Rijndam Rehabilitation Centre, Rotterdam; LeidenUniversity Medical Centre, Leiden; RijnlandsRehabilitation Centre, Leiden; SophiaRehabilitation Centre, Delft; Rehabilitation CentreDe Trappenberg, Huizen; Rehabilitation Centre HetRoessingh, Enschede.

Declaration of interest: The authors report noconflicts of interest. The authors alone are respon-sible for the content and writing of the paper.

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Appendix

The Gross Motor Function Classification System (GMFCS) levels for the children between their second and fourth birthday

Level I Children sit on floor with both hands free to manipulate objects. Movements in and out of floor sitting and standing areperformed without adult assistance. Children walk as the preferred method of mobility without the need for anyassistive mobility device.

Level II Children sit on floor but may have difficulty with balance when both hands are free to manipulate objects. Movements inand out of sitting are performed without adult assistance. Children pull to stand on a stable surface. Children crawl onhands and knees with a reciprocal pattern, cruise holding onto furniture and walk using an assistive mobility device aspreferred methods of mobility.

Level III Children maintain floor sitting often by ‘W-sitting’ (sitting between flexed and internally rotated hips and knees) and mayrequire adult assistance to assume sitting. Children creep on their stomach or crawl on hands and knees (often withoutreciprocal leg movements) as their primary methods of self-mobility. Children may pull to stand on a stable surface andcruise short distances. Children may walk short distances indoors using a hand-held mobility device (walker) and adultassistance for steering and turning.

Level IV Children sit on floor when placed, but are unable to maintain alignment and balance without use of their hands forsupport. Children frequently require adaptive equipment for sitting and standing. Self-mobility for short distances(within a room) is achieved through rolling, creeping on stomach, or crawling on hands and knees without reciprocalleg movement.

Level V Physical impairments restrict voluntary control of movement and the ability to maintain antigravity head and trunkpostures. All areas of motor function are limited. Functional limitations in sitting and standing are not fullycompensated for through the use of adaptive equipment and assistive technology. At level V, children have no means ofindependent movement and are transported. Some children achieve self-mobility using a powered wheelchair withextensive adaptations.

282 L. Enkelaar et al.

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