Static balance and developmental coordination disorder.

The development of static balance is a basic characteristic of normal motor development. Most of the developmental motor tests include a measure of static balance. Children with a developmental coordination disorder (DCD) often fail this item. Twenty-four children at risk for DCD with balance problems (DCD-BP) and 24 matched control children in the age range of 6-12 years participated in a detailed study of balance control. Additional groups of children (6-7 years, N=25; 10-11 years, n=16; with M-ABC scores >15th percentile) were selected randomly to study developmental changes in balance control in the age range of interest. Three experiments were conducted to examine developmental and clinical differences in the control of static balance. In the first, we measured the excursion of the centre of pressure (force-plate) in conditions with and without vision while standing still on one or two legs for 20 s. In the second experiment, EMGs were measured while standing on one leg. In the third experiment, in which only a subgroup of the DCD-BP and matched control children participated, a short unexpected force in the back lightly perturbed normal standing and EMG and force-plate responses were measured during balance recovery. In conditions of one-leg stance, children were not always able to maintain balance. Only epochs of stable postural control (7.5-20 s) were analysed. The results showed improvement of static balance with age, but only subtle differences between the DCD and control groups. Centre of pressure measures differed in the more difficult conditions. DCD-BP children had more difficulty standing on one leg with eyes closed. While standing on the non-preferred leg the EMGs of the DCD-BP children showed slightly more co-activation of the muscles of lower and upper leg. Perturbation of standing resulted in longer duration of recovery in the first trial in this group. Apparently DCD children learn to compensate for the perturbation within a few trials as well as control children do. The clear improvement with age shows that our measures of balance control are sensitive to detect changes. The general conclusion that may be drawn from this study is that under normal conditions static balance control is not a problem for children with DCD. Only in difficult or novel situations they seem to suffer from increased postural sway as a result of non-optimal balance control.