Transition From Rocking to Crawling: Postural Constraints on Infant Movement

Fifteen infants were videotaped weekly, beginning at 6 months, until they began to crawl. At each observation, infants were also videotaped as they reached to midline (to assess hand use preference). Of interest were the relative contributions of head orientation, hand use, and kicking for the development of crawling. During early stages, active orienting of the head to one side while prone was associated with particular patterns of both arm position and leg activity. At later stages, hand preference was associated with the transition from the stage of rocking to that of crawling: Infants rocked during a period when they showed ambilaterality during reaching, and they crawled when there was a strong hand preference. Thus, unimanual reaching promoted falling forward onto one hand and extending with the other. The co-occurrence of orienting, reaching, and kicking under particular postural and muscular constraints may account for the stage-like development of crawling.