Postural adjustments in sitting position : effect of development, training and brain lesions

The aim of the present study was to investigate the development of postural adjustments, and how this development could be affected by daily training and early brain lesions. To this end postural adjustments were assessed by means of multiple surface EMGs of neck, trunk and legmuscles and kinematics in various well documented groups of children. The youngest infants aged 5-6 months showed clear evidence that the basic level of postural control was functionally active prior to the development of independent sitting, because their postural adjustments were direction-specific. The latter means that they primarily activated the ventral muscles during backward body sway and the dorsal muscles during forward body sway. Characteristic of the adjustments of the young infants was the large variation in the combination in which the muscles were activated in concert. The variation decreased with increasing age resulting in selection of the most efficient postural response at 9-10 months of age. At this age also a capacity to modulate the direction-specific responses to taskspecific conditions, such as initial pelvis position developed. Selection and the development of response modulation were accelerated by daily balance training, Children with severe cerebral palsy (CP) displayed a total or partial loss of direction-specificity, in the children with milder forms of CP direction-specificity was intact. In the latter group of children the adjustments were more often stereotyped than in normally developing children. This was especially true for children with lesions in the periventricular white matter. In addition, children with CP and children born preterm with or without brain lesions showed deficits in the capacity to modulate postural activity with respect to body configuration. Some children lacked this capacity entirely, while others could adapt postural activity in the position which they often adopted during daily life. These data suggest that daily training might improve the reduced modulating capacity in the children with mild to moderate forms of CP