Independent sitting development and the emergence of associated motor components.

The purpose of this preliminary study was to examine the relationship between the emergence of independent sitting ability and the presence of underlying motor components (reflexes, automatic postural reactions, and flexion and extension movement patterns). Ten full-term, nonhandicapped infants were tested longitudinally for the presence of underlying motor components as they attained three performance levels of sitting ability between the ages of 4 and 7 months. A total of 26 observations was collected across the 10 infants. The time of each testing session was based on the infants' attainment of each successive sitting performance level. Underlying motor components were assessed at each testing session to determine whether a consistent sequence of component emergence developed and whether those components were associated with a specific performance level of sitting. The results indicated that no consistent sequential pattern of motor component emergence existed. The data showed that the pattern of underlying component emergence was highly variable across the infants at similar levels of sitting ability, although some components were associated highly with specific performance levels. The data suggest that the attainment of independent sitting in nonhandicapped infants is described best as a continuous developmental process, rather than a discontinuous "stage" phenomenon.