Abstract
Efficient voluntary action requires postural adjustments that compensate for potential balance disturbances before they occur. These anticipatory postural adjustments have been widely investigated in adults, but relatively little is known about their development, especially during infancy. This study examined the early development of anticipatory postural activity in support of pulling action while standing. A total of 34 infants between 10 and 17 months were tested. The task required infants to open a cabinet drawer to retrieve toys while a force resisting the pulling action was applied to the drawer. The experiment included between 9 and 13 pulling trials. The force resisting the pull was doubled after the first 4 initial trials and returned again to its original value after another 4 trials. Electromyographic activity from the gastrocnemius and biceps brachii muscles was recorded. The proportion of pulls involving anticipatory activity in the gastrocnemius muscles progressively increased between 10 and 17 months. In addition, infants with considerable experience in opening drawers learned to recruit greater strength of their anticipatory postural adjustments for heavier pulls. Implications for the role of motoric experience in anticipatory postural activity are discussed.
