Feedfoward postural adjustments associated with unilateral rapid arm motion in children aged 4- and 5-years and 10- and 11-years.

Abstract

Very little is known of the development of the feedforward postural control mechanism. The purpose of this study was to identify differences in this system between two different stages of development. Two groups of ten children, aged 4- and 5-years old and 10- and 11-years-old took part in this study. Electromyographic (EMG) data from the right anterior deltoid, right and left erector spinae, right and left hamstring muscles and vertical ground reaction force data from the left and right foot as well as the total body, were collected during unilateral rapid forward arm movement about the shoulder in the sagittal plane. EMG and force data were examined for activity 100 ms prior to onset and 70 ms post movement onset. Onset latencies, probability of recruitment and recruitment order were determined for all postural muscles. Onset latencies of changes in the vertical ground reaction forces as well as coefficients of variation were determined for the vertical ground reaction forces. In general, the 4- and 5-year old children demonstrated a similar postural muscle recruitment order as the 10- and 11-year old children. However, the 4- and 5-year old children had a larger proportion of the postural muscles being activated before the movement onset than the 10- and 11-year old children did. The probability of the 4- and 5-year old children recruiting the left erector spinae muscle was significantly less than that of the 10- and 11-year old children. The 4- and 5-year old children demonstrated greater intra-subject variability about the vertical ground reaction forces than did the 10- and 11-year old children. These data suggest that with development, the feedforward postural used in preparation for a unilateral rapid arm raise becomes increasingly consistent. A shift in the feedforward postural adjustment goal from safety to efficiency is proposed.