Multiple patterns of infant rolling in limb coordination and ground contact pressure.

Infants acquire the ability to roll over from the supine to the prone position, which requires body coordination of multiple degrees of freedom under dynamic interactions with the ground. Although previous studies on infant rolling observed kinematic characteristics, little is known about the kinetic characteristics of body segments in contact with the surface. We measured the ground contact pressure under the arms, legs, head, and proximal body segments using a pressure mat and their displacements using a three-dimensional motion capture system. The data obtained from 17 infants aged 9-10 months indicated that most of them showed 2-4 of 6 highly observed movement patterns, including 1 axial rolling, 2 spinal flexion, and 3 shoulder girdle leading patterns. The arms and legs had small contributions to the ground contact pressure in the axial rolling and spinal flexion patterns. The ipsilateral leg in relation to the rolling direction was involved in supporting the body weight in only 1 shoulder girdle leading pattern. The contralateral leg showed large peak pressure to push on the floor before rolling in 3 shoulder girdle leading patterns. The results indicate that infants can produce multiple rolling-over patterns with different strategies to coordinate their body segments and interact with the floor. The results of the analysis of the movement patterns further suggest that few patterns correspond to those reported in adults. This implies that infants generate unique motor patterns by taking into account their own biomechanical constraints.