From birth children develop the ability to control their posture in increasingly complex and demanding positions as well as during movement. This control has both sensory and motor aspects that change with maturation and result in increasingly efficient postural control. During the four to six year period considerable variability has been reported in children's postural control. The series of studies presented in this thesis aimed to investigate postural control in typically developing children and those with Developmental Coordination Disorder (DCD) at six, seven and eight years of age.
Typically developing children aged six, seven or eight years +/- eight weeks, were recruited from local schools (N=113) with approximately equal numbers of males and females, and were assessed once. Similar aged children referred to the Physiotherapy Motor Clinics at The University of Queensland, who satisfied the functional definition of DCD according to DSM IV and demonstrated sensory/motor problems on Physiotherapy Neurodevelopmental Assessment (PT-NDA) comprised the DCD subjects (N=54). In the DCD group there was a gender imbalance as expected (46 males, 8 females). DCD children were assessed on 3 occasions. All children in the study satisfied inclusion criteria and provided informed signed consent. The small group of children who withdrew were no different from those who continued in the study.
All of the studies used the same measures and reliability of the measures was established. Standard procedures were used and the assessor was blind to the child's group. Biographic variables recorded included age, height, weight, gender and fool length. Force plate measures included mean anteroposterior displacement of the Centre of Pressure (mAPCOP), velocity of sway, total distance of COP (TD), leg load asymmetry and percent of fool length used. These were measured in six normal and six tandem standing conditions. In normal standing children were tested when standing on the floor with eyes open, covered and when wearing the visual conflict dome. Then the measurements were repeated while the child stood on foam to reduce proprioceptive input. In tandem stance they were tested with the preferred and non-preferred leg placed forward, with eyes open, covered and when wearing the visual conflict dome. The balance task included was balance beam walking (heel-toe), recorded as the average number of steps achieved over 2 trials. PT-NDA performance was used to confirm the classification of DCD and to prescribe intervention programs for the DCD group but did not form part of the analyses.
Biographic variables were recorded and fool preference established. Six normal and 6 tandem stance conditions were tested in random order on the force plates, except that within each position the eyes open condition was tested first as a "baseline". Typical children were tested only once except for a small number (N=13) who returned within two weeks for the reliability component of the study. Children with DCD were tested initially, after a six month intervention period and again after a six month non-intervention period.
Study 1 explored the effect of biographic variables, age and altered sensory conditions on typical performance, and the correlation between study measures. Age and weight were the main biographic factors affecting performance. Typical children showed increased difficulty on study measures at 7 years compared to 6 years, but more mature responses at 8 years. Balance beam scores changed with age but did not relate to other measures. Sensory alteration adversely affected performance on study measures at all ages. Typical children used a strategy of "constraint" for control (limiting mAPCOP) while at the same time they increased velocity and total distance of the COP travelled.
Study 2 explored the same issues within the DCD groups, using data from the initial assessment. This group demonstrated similar (but weaker) patterns of response as the typical group, and used a similar "constraint" strategy. The age effect seen in typical children was not present in the DCD children. There was an advantage for DCD girls over DCD boys on some measures, unlike the typical group which showed no gender effect. However the small numbers of DCD girls require caution when interpreting results.
Study 3 evaluated the initial differences between the two groups on the study measures. It was found that while both groups demonstrated similar pattems of response, DCD children performed more variably than typical children. Postural control was not mature in either group by 8 years of age. DCD children used increased constraint for control compared with typical children but at the same time had increased sway velocity and total distance travelled. Children with DCD also had more difficulty than typical children in managing sensory conflict conditions (using conflict dome), and when proprioception was altered (stance on foam).
Study 4 explored the effect of a 6months home based intervention program in DCD children by comparing pre and post intervention measures. The children were re-evaluated after a further 6month non-intervention period. In addition, postural control in the DCD groups with/without intervention that were currently aged 7 or 8 years were compared. The postural control of children with DCD who received intervention was compared with typical children currently aged 7 or 8 years.
Improvements were shown after intervention, and retained unchanged after the non-intervention period. DCD children who received intervention performed similarly on measures of postural control to same-aged typical children. DCD children who received intervention had some advantages over the non-intervention group, showing increased use of a constraint strategy for control and decreased variance.
This study has provided detailed information about postural control in typically developing children at the ages of six, seven and eight years. Children with DCD of the same ages showed similar but more variable patterns of control overall, and were more affected by reduced proprioceptive input and visual conflict. Children with DCD who received six months of a home based intervention program showed improvement in their postural control as well as more convergence of postural control strategies than typical children.