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ORIGINAL ARTICLE

Postural Adjustment of Children With SpasticDiplegic Cerebral Palsy During Seated Hand Reaching inDifferent Directions

Yun-Huei Ju, MS, PT, Ing-Shiou Hwang, PhD, PT, Rong-Ju Cherng, PhD, PT

ABSTRACT. Ju Y-H, Hwang I-S, Cherng R-J. Posturaladjustment of children with spastic diplegic cerebral palsyduring seated hand reaching in different directions. Arch PhysMed Rehabil 2012;93:471-9.

Objectives: To examine the effect of reaching in differentdirections on postural adjustment in children with diplegiccerebral palsy (CP), and to examine the relationship betweenhand reach performance and postural adjustment, and betweenpostural control ability and postural adjustment.

Design: Cross-sectional study.Setting: A movement science laboratory at a medical

university.Participants: Children with CP (n12) and typically devel-

oping (TD) children (n16).Interventions: Not applicable.Main Outcome Measures: Two force platforms were used to

measure the ground reaction force (GRF) and center of pres-sure (COP) data. Absolute peak COP velocity, COP sway ratio(SR), and mean GRF in the anterior posterior direction duringthe acceleration and deceleration segments of a reaching taskwere the main outcome measures.

Results: Children with CP showed a greater absolute peakCOP velocity in the medial lateral direction, a smaller SR(wider COP pattern), and greater amplitude of force modula-tion (exaggerated postural adjustments) than TD children inlateral or medial reaches. There was a moderate correlation

between SR and total Pediatric Reach Test score. The chair SRwas also negatively correlated with the hand movement units.Conclusions: Children with CP showed wider, more crooked,

and less efficient COP patterns than TD children, especially onmedial or lateral reaches. Reaching medially or laterally in-volves trunk rotation, which produces more postural challengesthan reaching anteriorly to children with CP. The patterns ofpostural adjustments in children with CP were correlated withtheir postural control ability and hand-reach smoothness.

Key Words: Cerebral palsy; Rehabilitation. 2012 by the American Congress of Rehabilitation

Medicine

CEREBRAL PALSY (CP) is defined as a group of disordersof the development of movement and posture causing activ-ity limitation that are attributed to non-progressive disturbancesthat occurred in the developing fetal or infant brain.1(p572) Chil-dren with spastic diplegic CP, which is characterized by increasedmuscle tone, paresis, and involuntary motor control, and by moresevere involvement of the lower extremities than of other parts ofthe body, usually have difficulty in maintaining balance in anupright posture because of the postures unstable condition of ahigh center of mass and a small base of support.2,3 Therefore,many of their functional activities may be done in a seated posi-tion. Reach tasks in a seated position are 1 type of major func-

tional activity (eg, reaching for a book or a cup of water). Tounderstand how children with CP perform a seated reach task andhow they adjust to the task constraints may assist clinicians todevelop treatment strategies for improving the childrens dailyfunctioning.

The interrelationship between hand-reach and postural con-trol in typically developing (TD) children has been explored inseveral studies.4-7 The results showed that postural controlability affected reaching performance and that different de-mands of hand-reach changed postural adjustments.4-7 Infantsas young as newborns may show purposeful reaching move-ments once their heads are stabilized.4 Young children tendedto freeze their head position in a certain orientation relative tothe trunk as they reached forward, and their hand-reach per-formance was less efficient than an adults.5 Several studies

showed that children with CP would recruit additional trunkmotion as they reached forward. They may use additional trunkforward, trunk side-bending, or trunk rotation to compensatefor their impaired hand in order to fulfill the task goal. 8-12

From the Institute of Allied Health Sciences (Ju, Hwang, Cherng) and the Depart-ment of Physical Therapy (Hwang, Cherng), National Cheng Kung University,Tainan; and the Department of Physical Therapy, Kaohsiung Medical University, andthe Department of Rehabilitation, Kaohsiung Medical University Hospital, Kaohsiung(Ju), Taiwan.

Supported by the National Science Council, Taiwan (grant no. NSC 95-2314-B-037-069).

No commercial party having a direct financial interest in the results of the researchsupporting this article has or will confer a benefit on the authors or on any organi-zation with which the authors are associated.

Reprint requests to Rong-Ju Cherng, PhD, PT, Dept of Physical Therapy and Institute ofAllied Health Sciences, College of Medicine, National Cheng Kung University, 1 UniversityRd, Tainan City 701, Taiwan, e-mail: [email protected].

0003-9993/12/9303-00547$36.00/0doi:10.1016/j.apmr.2011.10.004

List of Abbreviations

AP anterior-posterior

BW body weight

COP center of pressure

COP-AP center of pressure in the anterior and

posterior direction

COP-ML center of pressure in the medial and lateral

direction

CP cerebral palsy

GMFCS Gross Motor Function Classification System

GMFM Gross Motor Function Measurement

GRF ground reaction force

GRF-AP ground reaction force in the anterior and

posterior direction

hand_MUs hand-reach movement units

ML medial-lateral

PPV point of peak velocity

PRT Pediatric Reach Test

SR sway ratio

TD typically developing

471

Arch Phys Med Rehabil Vol 93, March 2012
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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However, all the previous studies were done in children witheither hemiplegic CP or tetraplegic CP. The postural adjust-ment of children with diplegic CP during seated hand reachtasks is not clear. Moreover, few studies examine the posturaladjustment in terms of center of pressure (COP) performance,which is extracted by force plates. The relationship betweenpostural adjustment and hand performance at seated reach tasksin children with diplegic CP is also less examined.

Children with diplegic CP are characterized with impairmentof motor control more severe in lower extremity than in upperextremity. They present limited postural adjustment of thelower extremities in certain external perturbation conditions.13

Further, children with less motor ability had a more curvedhand path.14-16 The external environment, for example, seatsurface inclination, also affected reaching performance.15,17 Inaddition, hand reach performance and postural control ability issignificantly positively correlated in children; that is, the bettera childs postural control ability is, the more coordinated andefficient the childs hand reach performance will be.16

It has been proposed18 that the emergence of motor behavioris derived from the interplay between task, individual, andenvironmental constraints. The characteristics of individuals

interacting with task demands and the environmental contextconstraints affect the output of motor performance. Individualswith different characteristics may use different control strate-gies while performing the same task under the same environ-mental constraints. We previously16 showed that children withCP had a longer (curvier) hand traveling path as they reachedlaterally and medially than did TD children. Further, the effi-ciency of the hand traveling path was correlated with thechildrens postural control ability. Reaching laterally and me-dially were more challenging for postural control. Therefore, itis necessary to analyze postural adjustments to different tasksin order to understand how different postural abilities affectthese adjustments under different task constraints. In this arti-cle, we further analyze the COP data to examine the postural

adjustment. The COP data were simultaneously collected withhand performance, which was reported in another article.16

The purposes of this study were to test the following hy-potheses: (1) children with diplegic CP would demonstratedifferent patterns of postural adjustment from TD childrenbecause children with diplegic CP had insufficient posturalcontrol ability, (2) the patterns of postural adjustment would beaffected by the task constraints (reach directions) due to dif-ferent postural demands of the different task constraints onchildren, and (3) the patterns of postural adjustment would becorrelated to the childrens postural control ability.

METHODS

ParticipantsTwelve children with spastic diplegic CP and 17 TD children

participated in this study. The children with CP needed to be ofthe type of diplegia, capable of following instructions, andwithout visual difficulty (after correction). They also could nothave received any orthopedic/botulinum toxin treatment duringthe preceding 6 months before the onset of the study. Childrenwith TD should be free of any health conditions and develop-mental delay. The protocol of the study was approved by theInstitutional Review Board of Kaohsiung Medical UniversityChung-Ho Memorial Hospital with ethical considerations. Allthe parents or guardians of the participants signed the informedconsent, and the participants gave their oral assent.

Equipment

A six-camera motion capture system (Qqus 100 camera)a

with a 150-Hz sampling rate recorded the movement of reflec-tive markers that were attached to the third metacarpal head ofthe dominant (preferred) hand, and the container of the targetstuffed puppy. The target stuffed puppy was fixed in a con-tainer and hung from 1 of 3 spots on the ceiling. The height anddistance of the target were adjusted to each childs seat height

and arm length. The cameras were set up around the targetstuffed puppy and the participant, who sat on a 4-legged,height-adjustable, without back or arm support stool. Twoforce platforms,b 1 placed underneath the stool, the otherunderneath the participants feet, were used to measure theground reaction force (GRF) and COP of the participant with asampling rate of 150Hz. An infrared light beam device, whichsent a light beam across the reach path of the child just in frontof the target (a stuffed puppy), was used to determine if thechilds hand reached (a 5V signal on) or left the target (a 5Vsignal off). All the above equipments were synchronized dur-ing data collection.

Procedures

The detailed procedure of the clinical measurement and thestudy administration are described elsewhere.16 In brief, all theparticipants underwent anthropometric measurement, were askedto throw a ball to identify their preferred hands, and wereassessed with the Pediatric Reach Test (PRT) to quantify theirpostural control ability.19 The PRT was developed and modi-fied from the Functional Reach Test, which was originallydeveloped for measuring standing functional reach in adults.Because many children with CP are able to maintain only theupright position when sitting, the PRT is developed to measurethe functional reach distance of children with CP in both sittingand standing positions. During the test, each child was asked toraise his/her arm to shoulder height and reach forward as far asas possible without losing balance. The difference between theinitial to the final (farthest) hand position was recorded

as the functional reach distance. The functional reach distancesin the 3 reach directions (anterior, right, and left) in both thesitting and standing positions were summed together to becomethe total score of the PRT. Children with CP were also classi-fied using the Gross Motor Function Classification System(GMFCS) and assessed with Gross Motor Function Measure-ment (GMFM) dimensions D and E to quantify their grossmotor function.20,21

For the experimental procedure, children were seated on a4-legged height adjustable stool without a back or arm sup-ports, with their hips and knees at 90 angles, and their feet flaton 1 force platform. The stool was on the other force platform.Both of the positions of the stool and childrens feet wereindicated with tapes on the force platform for standardizationof data collection. Children were instructed to reach for a

stuffed puppy (the target) that was set at a distance of 120% ofeach childs arm-length and level with each childs shoulderheight in 3 directions: (1) anterior to the preferred hand, (2)deviated 40 laterally, and (3) deviated 40 medially from thesagittal plane of the preferred hand. The choice of 40 devia-tions for our study was determined due to the reason that itseems a comfortable range for children to reach with trunkpostural reorientation and without too much feet movement.

The starting position of the preferred hand was on the childslap; a sticker on the lap indicated where the hand was supposedto return to. The other hand was positioned along the trunk andrelaxed. A verbal signal was given to initiate the reach-and-return task. The pace of the task was modulated with a metro-

472 POSTURAL ADJUSTMENT OF CHILDREN WITH CEREBRAL PALSY, Ju



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nome at a frequency of 46 beats per minute to control the reachvelocity to diminish the potential influence of different reachvelocities on COP performance in task and group conditions.22

The children were allowed to practice several times to get usedto the pace. Each task was repeated at least 6 times. Thesequence of reaching direction was randomly assigned.

Data Reduction and Analysis

Qualisys Tracker Manager software (version 2.0.387)

a

wasused to convert the raw data of the position from the camerasinto 3-dimensional coordinates and to calculate force and COPdata from the 2 force platforms. The videos were used to checkthe reach-and-return movements with the Qualisys TrackerManager program while defining the following events: whenthe reach began, when the target was touched, when the targetwas left, and when the return ended. The raw data of handposition, GRF, and COP were filtered using a low-pass filterwith a cutoff frequency of 5Hz.23 The beginning of the reachwas defined as a continuum of changes in hand velocity above5% of peak velocity. The end of the return was defined as acontinuum of changes in hand velocity below 5% of peakvelocity. Touching the target and leaving the target were de-fined by 5-V signals as the hand touched (signal on) and left

(signal off) the target. All the COP and GRF data were rotatedwith a rotation matrix, which derived from task directionsrelative to the sagittal plane of the shoulder of the preferredhand for data comparison in 3 reach directions.24 Through thisprocedure, the rotated anterior-posterior (AP) axis was alignedwith the target direction, and the rotated medial-lateral (ML)axis was perpendicular to the rotated AP axis. Thus, the forceand COP data of the 3 reach tasks (3 directions) could becompared with the same coordinate system: the x axis (APdirection) orienting with reach direction and the y axis (MLdirection) orthogonal to the x axis. The data of the COP derivedfrom chair and feet were further combined to get a mergedCOP based on Winter et als25 equation. The data of the GRFand COP while the child was reaching for the target (from handonset to touching the target) are reported. The variables of

interest include hand-reach movement units (hand_MUs), swayratio (SR), and mean ground reaction force in the anterior andposterior direction (GRF-AP) during the hand acceleration anddeceleration segments of reaching for the target.

The SR was defined as the cumulative AP path lengthdivided by the ML path length.17 The SR represents COP

configuration in terms of the postural sway pattern. If the SR is1, it means that the cumulative AP length is equal to the MLlength. Therefore, the greater the SR, the narrower the COPconfiguration. A hand_MU is defined as 1 acceleration and 1deceleration segment of hand-reach velocity.23 The smaller thenumber of movement units, the smoother the hand reach. MeanGRF-AP during acceleration and deceleration segments wascalculated separately.26 The point of peak velocity (PPV) of thehand was defined. The hand acceleration during reach-out wasdefined from hand onset to hand PPV, and the hand decelera-tion was defined from hand PPV to the end of reach-out (handtouching the target). A positive GRF-AP means braking actionand a negative one means pushing action. If the mean GRF-APis between 0.1% and 0.1% of body weight (BW), it iscategorized as 0 (small magnitude of force); if it is less than0.1% or more than 0.1% of BW, it is categorized as 1 (greatmagnitude of force).

For each of the above-mentioned variables, the values of 5trials were averaged for each participant, and each directionwas used in the statistical analyses. The primary analyses weremultivariate analysis of variance to compare group effect andto compare task effect as the repeated factor for COP variables.Subsequent Fisher least significant difference post hoc multiple

comparisons were done, and the Fisher exact test was used tocompare the differences of distribution on force amplitudebetween groups. Pearson product-moment coefficients of cor-relation were used to examine the relationship between COPperformance and postural control ability (total PRT score) orhand-reach performance (hand_MUs). In addition, the relation-ships between 120% arm length and total PRT score weretested with Pearson product-moment coefficient of correlation.Significance level was set at P.05.

RESULTS

Demographics

One of the TD children was excluded because of an outlierin the data. There were no significant differences in age (CP:

107.8mo vs TD: 110.9mo; P.723), sex distribution (CP: 5girls, 7 boys vs TD: 10 girls, 6 boys; P.274), and BW (CP:26.7kg vs TD: 30.3kg; P.170) between the 2 groups ofchildren. However, children with CP were significantly shorterthan TD children based on the seated height data (92.7cm vs102cm; P.005). Children with CP had significantly shorter

Table 1: Characteristics of Gross Motor Function and Postural Control Ability in Children With CP

ID Sex Age (mo)

Seated Height

(cm)

120% Arm Length

(cm)

Weight

(kg) GMFCS

Total PRT

Score (cm)

GMFM

Score (%)

1 G 119 94.5 67.2 26.5 3 55.3 89.0

2 G 120 96.0 63.6 24.0 4 31.1 80.8

3 B 124 100.0 67.2 38.0 4 25.1 36.3

4 G 129 93.8 64.8 22.4 4 27.5 53.15 B 77 86.0 57.8 18.7 3 42.9 92.8

6 B 128 103.0 72.0 36.0 3 77.5 87.6

7 G 118 101.0 64.8 33.6 2 101.9 88.5

8 B 68 81.0 57.6 17.6 3 26.7 85.1

9 B 82 82.5 55.2 22.1 4 36.9 52.3

10 B 118 101.0 71.8 36.0 3 46.5 85.5

11 G 72 77.0 54.7 18.0 4 18.8 42.3

12 B 138 96.8 66.2 27.1 3 71.1 87.2

Average SD 107.825.2 92.78.9 63.66.0 26.77.5 NA 46.825.3 73.420.8

NOTE. The GMFM score was averaged with the subscores of sitting and standing dimensions. The seated height includes the height of head,trunk, pelvis, and stool.Abbreviations: B, boy; G, girl; ID, patient identification number in the study; NA, not applicable.

473POSTURAL ADJUSTMENT OF CHILDREN WITH CEREBRAL PALSY, Ju



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120% arm length than TD children (63.6cm vs 69.3cm;P.029). The characteristics of children with CP are presentedin table 1. Their gross motor function ranged from mild tosevere: levels II to IV of the GMFCS. The total PRT score wassignificantly, positively correlated with 120% arm length(r.584, P.001), which means the less the postural controlability, the shorter the 120% arm length (shorter reach dis-tance). The difficulty of reach task for each participant could becontrolled with this standardized arm reach distance.

Characteristics of COP During Reach-Out

Figure 1 presents a representative COP pattern of a child

with CP (ID: 9) and a comparison (age- and sex-matched) TDchild (ID: 13). Unsurprisingly, the child with CP has lesspostural control ability (total PRT score: 36.9) than the TDchild (total PRT score: 80.6). Figure 1 shows that the child withCP had a curvier pattern of COP than the TD child. This childwith CP tended to utilize a loop pattern of weight shift on theupper body (chair), while the TD child showed a rather straightpattern of weight shift.

Table 2 presents the group means and SDs of peak COPvelocity and SR. The result of SR was further demonstratedwith figure 2.

Absolute peak COP velocity. Children with CP showedsignificantly greater peak COP velocity in the anterior and

posterior direction (COP-AP) than TD children, especiallywhen they reached medially. In general, children with CPshowed greater ML velocity than TD children in anterior andlateral reach tasks. The merged peak COP velocity in themedial and lateral direction (COP-ML) showed a significantinteraction effect, which means that the 2 groups madedifferent COP-ML adjustments. Children with CP showedsimilar high COP-ML velocity in all 3 reach directions, butTD children showed progressive changes of COP-ML ve-locity, especially at medial reach (see table 2).

COP configuration. Children with CP had a wider chairCOP pattern (less SR) and merged SR than TD children on

anterior and lateral reaches, but not on the medial reach (seetables 2 and 3). Children with CP had less feet SR on anteriorand lateral reaches, but greater feet SR on the medial reach thanTD children. For task effect, children had a greater chair andmerged SR (a narrower COP) when reaching laterally thanwhen reaching medially (P.001), and a smaller SR (a widerCOP) when reaching medially than when reaching anteriorly(P.001). Feet SR especially was significantly different in all3 reach directions. Generally, there were observable interactioneffects between group and task. For chair and merged SR,children with CP had a rather wide postural sway in all taskconditions; TD children apparently had a narrower COP swayon anterior and lateral reaches and a smaller SR when reaching

-6 -4 -2 0 2 4-4

-2

0

2

4

6

Chair

-6 -4 -2 0 2 4-4

-2

0

2

4

6

Feet

-6 -4 -2 0 2 4-4

-2

0

2

4

6

-6 -4 -2 0 2 4-4

-2

0

2

4

6

-6 -4 -2 0 2 4-4

-2

0

2

4

6

-6 -4 -2 0 2 4-4

-2

0

2

4

6

-6 -4 -2 0 2 4-4

-2

0

2

4

6

Chair

-6 -4 -2 0 2 4-4

-2

0

2

4

6

Feet

-6 -4 -2 0 2 4-4

-2

0

2

4

6

-6 -4 -2 0 2 4-4

-2

0

2

4

6

-6 -4 -2 0 2 4-4

-2

0

2

4

6

-6 -4 -2 0 2 4-4

-2

0

2

4

6

CP (ID9) TD (ID13)

Posterior-AnteriorDirection(cm)

Medial-Lateral Direction (cm)

Fig 1. A comparison of a COP ex-cursion in a representative trial of aboy with CP (identification number[ID] 9; age: 82mo; seated height:82.5cm; total PRT score: 36.9) andan age-matched TD boy (ID 13; age:81mo; seated height: 87.5cm; totalPRT score: 80.6) in all 3 reach direc-tions (top: anterior; middle: lateral;and bottom: medial). A square indi-cates the beginning of reaching forthe target, and a star denotestouching the target.




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medially. For feet SR, children with CP had a rather wide COPpattern, but TD children had a different COP sway pattern in all

3 reach directions (see table 2).Mean GRF-AP During Hand Acceleration and

Deceleration Segments

A mirror phenomenon of the GRF between body (chair) andlegs (feet) is depicted in figure 3. If we categorize the meanforce between0.1% and 0.1% of BW as 0 and the mean forcegreater than 0.1% or lower than0.1% of BW as 1, we see thatchildren with CP had a tendency to use counterbalance forcebetween chair and feet. During the acceleration segment, agreater proportion of children with CP (lateral reach: 4/12;medial reach: 5/12) used more chair-pushing or braking forcethan TD children (lateral reach: 0/16; medial reach: 0/16)(Fisher exact: P.024 and .008). The same difference was truefor feet data when reaching laterally (Fisher exact: P.024).

During the deceleration segment, both groups used moreapparent braking or pushing force than the acceleration seg-ment. Interestingly, a greater proportion of children with CPused apparent chair-pushing force (10/12) when reaching me-dially than TD children (6/16) (see fig 2). Most of the childrenwith CP showed apparent feet pushing and braking force (an-terior: 11/12; lateral: 10/12), but few TD children did (anterior:7/16; lateral: 5/16) (Fisher exact: P.011 and .008). In addi-tion, several children with CP used more counterbalance forcebetween chair and feet, such as participants CP3 and CP11,

who presented low total PRT scores in terms of poor posturalcontrol ability (see table 1).

Correlations Between COP Performance and Postural

Control Ability or Smoothness of Hand Traveling Path

The total PRT score showed that children with CP had lowerscores than TD children (46.8 vs 117.2, t7.800, P.001),which means that children with CP have less postural controlability than TD children. The total PRT score and SR werepositively correlated for anterior and lateral reaches (table 4),which means that the better the postural control, the narrowerthe COP displacement. Chair SR was negatively correlatedwith hand_MUs, which means that the narrower the COPdisplacement, the fewer the hand_MUs and the smoother thehand traveling.

DISCUSSIONThe purposes of this study were to test the following hy-

potheses: (1) children with diplegic CP would demonstratedifferent patterns of postural adjustment from TD childrenbecause children with diplegic CP had insufficient posturalcontrol ability, (2) the patterns of postural adjustment would beaffected by the task constraints (reach directions) due to dif-ferent postural demands of the different reach tasks on chil-dren, and (3) the patterns of postural adjustment would becorrelated to the childrens postural control ability.

Table 2: Dependent Variables of COP Performance During Reach-Out Phase in the CP and TD Groups

Group/Variable

Anterior Lateral Medial

Chair Feet Merged* Chair Feet Merged* Chair Feet Merged*

CP group

Peak COP-AP

velocity 19.779.27 23.148.05 13.975.42 20.998.73 26.3010.54 16.726.12 17.196.64 23.6511.78 14.095.88

Peak COP-ML

velocity 14.744.73 24.766.26 13.154.00 16.176.57 24.429.28 15.245.35 18.267.04 25.668.91 16.273.77

SR 1.540.56 1.000.18 1.150.31 1.510.39 1.230.46 1.150.37 1.000.56 1.060.43 0.940.52

TD group

Peak COP-AP

velocity 21.859.16 18.665.00 14.575.07 28.8012.81 28.2212.02 22.059.22 21.447.64 16.833.88 16.275.08

Peak COP-ML

velocity 10.184.12 17.066.83 8.723.27 12.164.49 17.707.05 11.012.92 18.566.74 22.647.84 16.935.60

SR 2.590.98 1.170.23 1.880.59 2.670.86 1.780.38 2.210.78 1.300.46 0.820.15 1.030.42

NOTE. Peak COP velocity was measured in cm/s. Values are mean SD.*The data of the chair and feet were merged.

Reach directions

anterior lateral medial

Swayratio(SR)

0

1

2

3

4

anterior lateral medial0

1

2

3

4

CP

TD

Chair SR Feet SR

Fig 2. The changes of the COP SRat all 3 reach directions in bothgroups. The dash line is plotted atSR 1, which means the COP-APcumulative path is equal to theCOP-ML path.




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Compared with TD children, children with CP had a greaterpeak COP-ML velocity, a wider COP sway on anterior andlateral reaches, and exaggerated force modulation on medialreaches. This suggests that children with CP encounter poten-tial threats of instability and inefficient weight shifting duringreach while seated, which is similar to young children withimmature postural stability.5

When children reached laterally, peak COP-AP velocity wasincreased, but when they reached medially, peak COP-ML

velocity was increased, even though the COP data were ad-justed with the reach direction. COP configuration, in terms ofSR, also showed the widest COP pattern at medial reach. Thisfinding supports the hypothesis that motor output is influencedby task demand.18

One interesting finding of this study is the role of lowerextremities in seated reach tasks. Children with CP showedconsistently wide feet COP patterns in all 3 reach tasks; how-ever, TD children had different feet COP patterns among thesetasks. This finding suggests that TD children adjusted theirposture to meet the different task demands. Children with CP,however, may have difficulty using their legs to assist withpostural adjustments for seated reach tasks. This difficulty in

using legs for postural adjustment has been reported in childrenwith CP while they faced a fast balancing threat in standingposition.13 Our study further showed that children with diplegicCP would encounter such difficulty while they performedseated reach tasks.

For the interplay between upper body and legs, children withdiplegic CP made forceful and exaggerated postural adjust-ments; unlike the TD children, they could not make subtlepostural adjustments during the reach tasks. A great proportion

of children with CP used pushing force on the chair andbraking force on their feet during deceleration of medial reach.A possible explanation is that children with CP perceived thecontralateral reach demands and recognized the need for trunkrotation in order to reorient their body position to successfullytouch the target. Therefore, they might make exaggerated trunkadjustments to meet the task constraint with several small trunkadjustments (eg, loop COP patterns). Such results showedsome similarities with previous studies that children with CP,although with other types of CP, use trunk motion as a com-pensatory strategy to finish reach tasks.8-12

Medial reach involves trunk rotation. People need to antic-ipate this and preplan how to adjust it without changing hand-

Table 3: Summary Table of the Statistical Analyses Results of COP Performance

Variable

Group Task Interaction


F3,25 P F3,25 P F3,25 P F2,26 P F2,26 P F2,26 P F2,26 P F2,26 P F2,26 P

Peak COP-AP

velocity 2.01 .139 3.69 .026 1.50 .241 5.15 .013 8.52 .002 9.30 .001 2.06 .149 2.70 .087 2.17 .136

Peak COP-ML

velocity 4.29 .015 3.71 .025 4.66 .010 16.76 .001 3.90 .034 25.47 .001 2.75 .083 1.93 .166 4.08 .029SR 6.02 .003 5.78 .004 6.48 .002 19.69 .001 13.44 .001 10.22 .001 3.87 .034 8.10 .002 4.59 .020

*The data of the chair and feet were merged.

Segments

a d a d a d

meanAP_

GRFoffeet(%ofBW)

-2.0

-1.0

0.0

1.0

2.0

-2.4

-2.2

-1.8

-1.6

-1.4

-1.2

-0.8

-0.6

-0.4

-0.2

0.2

0.4

0.6

0.8

1.2

1.4

1.6

1.8

2.2

2.4

-2.0

-1.0

0.0

1.0

2.0

a d a d a d

meanAP_

GRFofchair(%ofBW)

-2.0

-1.0

0.0

1.0

2.0

-2.4

-2.2

-1.8-1.6

-1.4

-1.2

-0.8-0.6

-0.4-0.2

0.2

0.40.6

0.8

1.2

1.41.6

1.8

2.2

2.4

-2.0

-1.0

0.0

1.0

2.0

TD

Segments (a: acceleration, d: deceleration)

a d a d a d

meanAP_

GRFoffeet(%ofBW)

-2.4

-2.2

-1.8

-1.6

-1.4

-1.2

-0.8

-0.6

-0.4

-0.2

0.2

0.4

0.6

0.8

1.2

1.4

1.6

1.8

2.2

2.4

-2.0

-1.0

0.0

1.0

2.0

CP Anterior Lateral

a d a d a d

meanAP_

GRFofchair(%ofBW)

Medial

-2.4

-2.2

-1.8-1.6

-1.4

-1.2

-0.8-0.6

-0.4-0.2

0.2

0.40.6

0.8

1.2

1.41.6

1.8

2.2

2.4

-2.0

-1.0

0.0

1.0

2.0 CP11CP8CP8

CP11CP3 CP3

CP3CP9

CP11CP3 CP3

CP8CP8

CP11

A

B

Fig 3. A profile of mean pushingand braking forces for each partic-ipant with CP and TD during handacceleration and deceleration in all3 reach conditions (A, chair data; B,feet data). Positive GRF-AP repre-sents the braking effect, and nega-tive GRF-AP represents the push-ing effect.




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trunk coordination.27,28 Because children with CP have moredifficulty in anticipating control and controlling coordinationbetween body segments than TD children,29-31 they mightchoose different strategies to cope with this specific task.Interestingly, when we further examined the total PRT score ofthese children with CP who showed significant interplay be-tween chair and feet (eg, on lateral and medial reaches [see fig3]), we found low total PRT scores, such as those for patientIDs 3, 8, 9, and 11 (see table 1). Three of these children, IDs

3, 9, and 11, were functioning at GMFCS level IV, whichmeans that they were severely impaired in motor function.Although patient 8 was functioning at GMFCS level II (highfunction level), he was the youngest participant in this study.This observation agrees with the hypothesis that different mo-tor solutions may be used because of different individual con-straints.18,32 We hypothesize that children with poor posturalcontrol may need exaggerated force modulation between theinterplay of the chair (trunk) and feet. Moreover, the motorexperience can also affect the strategy of postural adjustment.Younger children make less efficient postural adjustments thanolder children.13

There were significant interaction effects between group andtask in the SR. This means that children with CP and TDchildren reacted differently when facing different task de-

mands. For the chair SR, children with CP presented a wideCOP sway in all 3 reach conditions (mean, 1.01.5), whilechildren with TD kept a narrow COP (large SR) sway onanterior and lateral reaches (mean, 2.62.7), and then appar-ently reduced the SR at medial reach (mean, 1.3) (see fig 2).This suggests that children with CP may perceive their indi-vidual constraints and choose a wide COP pattern (a possiblealternative pattern) to compensate for their insufficient posturalcontrol ability to achieve the task goal. It is possible thatchildren with CP did not shift weight directly toward thereaching direction. In contrast, they looked for a safer weightshift first and then reoriented the body toward the target direc-tion. As displayed in figure 1, the child with CP did not shiftweight outward directly like the TD child. It has been pointedout that people may manage their postural control for reasons

of safety and efficiency.29

Children with CP might anticipatethe possible internal perturbation for reach out (eg, lateralreach) and decide to keep their body at the safe zone first(safety) based on their postural control constraint. Later, theyreoriented their body to reach direction (efficiency). Therefore,they used a curved COP pattern to manage the reach task(control stability first, and then efficiency). Such results werealso in agreement with the findings of previous studies.33-35

Children with CP perceive their neuromuscular or biomechani-cal constraints and develop their specific motor patterns oralignment to deal with task demands, such as firing musclesfrom proximal to distal, increased coactivation, or fixing flexedtrunk posture as balance is disturbed.33,34

An alternative explanation may be that the children with CPmight be near their limit of stability in reaching, relative to TDchildren. Therefore, children with CP had more balancingchallenges than TD children. Further study should be done tosee whether TD children showed the similar pattern whenplaced in the similar condition.

For the feet SR, children with CP only had small changes ofSR when reaching laterally (mean anterior: 1.0; lateral: 1.2; andmedial: 1.1), whereas TD children made significantly different

SR adjustments when reaching in different directions (meananterior: 1.2; lateral: 1.8; and medial: 0.8) (see fig 2). Thesedifferences between groups were significant for each direction.This result further reflects the problem of insufficient control ofthe lower legs when children with diplegic CP are involved inseated reaching tasks. Such result was in agreement with Burt-ner et als13 finding that children with diplegic CP had troubleusing their leg to manage postural adjustment, especially in themediolateral direction. Children with diplegic CP did encoun-ter problems in managing leg stability.

Correlations between smoothness of the hand traveling path(hand_MUs) or postural control ability (total PRT score) andCOP pattern (SR) are evident. The SR was positively corre-lated with the total PRT score on anterior and lateral reaches,but not on medial reaches. This means that children with less

postural control ability, shown by a lower PRT score, have awide COP pattern of reach. This result is consistent with ourprevious study.17 The better the postural stability, the greaterthe SR. However, this relationship disappeared with medialreach. A possible explanation is the task constraint. Whenchildren reach medially, they intentionally increase lateral-medial sway. The different motor coordination may be con-strained by reaching medially, as reported in other studies.27,36

In such a situation, it is impossible to use this variable todifferentiate between these 2 groups. This finding is also evi-dent with the significant task effect in our study. All partici-pants had a smaller SR on medial reaches than on anterior andlateral reaches.

Study Limitations

One of the limitations of the study was the small sample size.Another limitation was the limited type of CPdiplegic CP.Only children with diplegic CP were included in the study.Therefore, the results may not be generalized to other types ofCP. A third limitation was the possible confounding effect ofthe hand reach velocity. A metronome was used to control thepace of hand reach. However, children with CP generallyshowed slower hand reach velocities than TD children. Futurestudy may examine the effect of reach velocities on posturaladjustment. The last limitation is task difficulty (the reachingdistance relative to the individual limit of stability). It is pos-sible that 120% arm length reaching distance would be close tothe limit of stability in some children but not in the others, and

Table 4: Correlation Coefficient Between COP SR and Postural Control Ability (total PRT score) or Smoothness of the Hand TravelingPath (Hand_MUs)

Variable

Anterior Lateral Medial


r P r P r P r P r P r P r P r P r P

Total PRT score .478 .001 .350 .068 .542 .003 .618 .001 .512 .005 .614 .001 .282 .146 .267 .170 .181 .358

Hand_MUs .449 .017 .260 .181 .430 .022 .445 .018 .156 .427 .361 .059 .474 .011 .155 .431 .316 .102

NOTE. Pearson product correlation coefficient was used.*The data of the chair and feet were merged.




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therefore the task appeared more difficult for some childrenthan for others. However, the significant positive correlationbetween the PRT score and the 120% arm length of our studyrepresents that the less the childs limit of stability, the shorterthe childs 120% arm length. The task difficulty should besomehow controlled with the standardized 120% arm length.Future study may examine if TD children, when facing a reachtask close to their limit of stability, would demonstrate the

similar movement pattern like children with CP did in thisstudy.

CONCLUSIONS

Children with CP showed wider, more crooked, and lessefficient COP patterns than TD children. In addition, suchdifferences were bigger on medial or lateral reaches. Reachingmedially or laterally involves trunk rotation, which producesmore postural challenges than reaching anteriorly. In such taskconditions, children with CP face additional postural controlchallenges. Therefore, they make different postural adjust-ments, such as a curvier COP displacement, wide COP excur-sion, or forceful regulation of the upper body and legs. Thepatterns of postural adjustments in children with CP were

correlated with their postural control ability and hand-reachsmoothness.

Acknowledgment: We thank Yi-Hsin Yang, PhD, of the Statis-tical Analysis Laboratory, Department of Medical Research, Kaohsi-ung Medical University Hospital, Kaohsiung Medical University, forassistance with the statistical analysis and interpretation.

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Suppliersa. Qualisys AB, Packhusgatan 6, S-411 13 Gteborg, Sweden.b. 9286 & 9286AA Force plates; Kistler Instrumente AG Winterthur,

Eulachstrasse 22, CH-8408 Winterthur, Switzerland.



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Ajustes Posturales en Alcance en Sedenteen Diplejia