Fits, Ingrid Barbara Maria van der

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Dissertations of the University of Groningen

   University of GroningenPostural adjustments during reachingFits, Ingrid Barbara Maria van derIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:2009Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Fits, I. B. M. V. D. (2009). Postural adjustments during reaching: normal and abnormal development. s.n.CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 28-12-2022SuuuenyThe aim of the present study is to investigate the neurophysiological mechanismsunderlying normal and abnormal development of postural adjustments duringreaching movements in infancy. Adequate postural control is essential for our dailyfunctioning' The normal development of postural adjustments facilitates thedevelopment of fluent motor performance, of a successful social interaction andcommunication, and of cognitive abilities. Abnormalities in the development ofpostural control are frequently reported in preterm children and children withcerebral palsy, but knowledge on the pathophysiological development of posturalcontrol is only limited. Still, such knowledge is a prerequisite for the understandingof the effects of current therapeutical interventions and for the development ofproper methods to treat postural dysfunctions.Chapter 2 describes the neural structures which are involved in posfural control,and briefly reviews their development. Chapter 3 summarizes the strucfuraldevelopment of the central nervous system (CNS), and the motor development inhealthy full-term infants, preterm infants and infants with cerebral palsy.The chapters 4-8 present results of our sfudies on the organization of posturaladjustments accompanying reaching movements. After the study on posturaladjustments in adult subjects, we longitudinally studied the development of posturaladjustments between the ages of 3 and 18 months in three groups of infants: healthyfull-term infants, relatively healthy preterms, and infants with cerebral palsy.During each session we recorded surface EMGs of arm, neck, trunk, and leg muscleswhile the subjects were placed in various sitting and lying positions. O^ly in theadult subjects EMG activity was also recorded during stance. Simultaneously, werecorded the whole session on video. In addition, simultaneous kinematic recordingswere made in the adult subjects and in an extra sample of healthy full-terms, whowere only studied once, between the ages of 9 and ls months.The results of the adult study are reported in chapter 4. A remarkable finding wasthat the adults consistently used a specific movement strategy to perform the armmovement (i.e. pointing towards a visible target). Despite identical instructions, halfof the subjects started the pointing movement with a flexion of the shoulder whilekeeping the arm extended throughout the movement. These subjects activated thedeltoid (DE) as the first arm muscle. The other subjects initiated the movement witha slight flexion of the elbow after which an elevation and extension of the arm178 Summaryfollowed. These subjects used the biceps brachii (BB) as the prime mover. Thepostural data clearly demonstrated that the organization of the postural adjustmentsduring the unilateral pointing movements depended on the movement strategy.Another important finding concerned the position dependency of the posturaladjustments. During stance the dorsal postural muscles (which were consistentlyactivated before their ventral antagonists; direction specificity) were recruited in acaudal-to-cranial order. This means that the leg muscles were activated before thetrunk and the neck muscles. But in the various sitting and lying positions this orderwas reversed. Furthermore, we demonstrated that the postural adjustmentsdepended on a variety of task-specific constraints, such as the arm movementvelocity, the position of the pelvis and the trunk at movement onset, and the load ofthe task. The task-load effects were studied by the performance of two additionalseries of pointing movements, one consisting of bilateral movements and the other ofunilateral movements with an additional weight (500 gr or *0.7% of body weight).Chapter 5 deals with the organization of postural adjustments during the periodin which successful reaching emerges in healthy infants. The onset of successfulreaching - around 4-5 months - and the development of the accompanying posturaladjustments were related more closely to the postmenstrual age of the infants (whichis denoted by the number of weeks after the first day of the last menstruatial periodof the mother) than to their postnatal calendar age. This suggests that endogenousmaturational mechanisms are particularly involved in the development of successfulreaching and the accompanying postural activity. Already before reaching resultedin successful grasping, the goal-directed arm movements were accompanied by ahigh, but variable amount of postural activity. The postural activity already showedthe adult characteristics of direction specificity and, in a crude way, the positiondependency (lying versus sitting). With increasin1 a1e, the amount of posturalactivity decreased significantly, but the temporal organization of the activity whichremained, was more consistently organized in the top-down order than that atearlier ages.In chapter 6 the normal development of postural adjustments during reaching ininfants between 6 and 18 months is described. After the period of low posturalactivity at 6 months, ample postural activity reappeared at 8 months. From that ageonwards the amount of postural activity continuously increased till L8 months. Theperiod of little postural activity around 6 months probably served as a transitionphase, as after this transition the ability emerged to adapt the postural adjustments; rSummaryto task-sthe pelvoccurredwhich wactivatioable to a(56 gr o:adult stuChaplAt the aother se'high amFurtherr:be adaplto modufrom priIn ch;cerebrala spasticthe 'putrespons(pretermadjustmperformform ofadjustm,precludtIn thrlarge vareachinlvariabiliall the irisk forinfants iadjustmSummaryrover. Theljustmentst strategy.e posturalonsistentlyruited in abefore the; this orderdjustmentsmovementthe load ofadditionallhe other of'weight).the periodi successfulng posturalmts (whichrtial periodndogenousisuccessfulrg resultedmied by uly showedre positionposturalrity whichan that ateaching inr posturaln that agenths. ThetransitionijustmentsSummaryto task-specific constraints, such as the arm movement velocity and the position ofthe pelvis at movement onset. Between 12 and L5 months a second transitionoccurred. From 15 months onwards infants developed anticipatory postural control,which was reflected by the consistent activation of one of the neck muscles before theactivation of the first arm muscle. Moreover, from this age onwards the infants wereable to adjust postural activity to an increased task-load, i.e. a small weighty bracelet(56 gr or x.0.7"/" of body weight, comparable to the additional weight used in theadult study).Chapter 7 concerns the development of postural adjustments in preterm infants.At the age of 18 months five infants showed minor neurological dysfunctions, theother seven were neurologically normal. The preterm infants showed a remarkablehigh amount of postural activity during reaching movements at all ages studied.Furthermore, the postural adjustments were temporally disorganized and could notbe adapted to the task-specific conditions. We proposed that the preterms' disabilityto modulate the postural responses might be related to a reduced capacity to learnfrom prior experience.In chapter 8 the results of the study on the postural development in infants withcerebral palsy are presented. Five of the infants developed a spastic hemiplegia, onea spastic tetraplegia and one a spastic tetraplegia with athetosis. In the infants withthe 'pure' spastic forms of cerebral palsy the basic organization of the posturalresponses was apparently intact. The main problem of these infants - like that of thepreterm infants - consisted in a deficient capacity to modulate the posturaladjustments. This deficit was attributed to a combination of an impaired motorperformance and sensory integration. The child with the mixed (spastic-dyskinetic)form of CP showed distinct abnormalities in the basic organization of the posturaladjustments. It was suggested that such a fundamental deficit in postural controlprecluded the development of independent sitting.In the final chapter (Chapter 9) we reflect on the results our studies. In general, alarge variation was present within the postural response patterns accompanying thereaching movements. This large variability can be regarded as a sign of primaryvariability. The finding that a multitude of posfural response patterns is present inall the infants studied, suggests that the primary variability is retained in infants atrisk for the development of postural dysfunctions. A common finding in the preterminfants and the infants with cerebral palsy was their disability to adapt the posturaladjustments to task-specific constraints, i.e. to develop appropriate adaptive1.79180 Summaryvariability. Likely, deficits in the processing of sensory information are involved inthe abnormal development of postural adjustments in both groups. We argued thatthe underlying mechanisms of this deficit differed. This has consequences fortreatment of the postural abnormalities in these groups of infants. The posturaldevelopment in preterm infants might be enhanced by a combination of relaxationand balance exercises. The postural development of children with cerebral palsymight be improved when the infants are placed in sitting devices with a backwardtilted seat-surface - providing a biomechanical compensation for the forwarddirected body sway induced by the reaching movement. Furthermore, explicitafferent cues should be provided in order to facilitate the processing of sensoryinformation in this particular group of children.

Postural adjustments during reaching:normal and abnormal development.

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Postural adjustments during reaching:normal and abnormal development.

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