Early development of coordination for the sit-to-stand task

The task of standing up from sitting requires coordinated movements of multiple body segments. This article presents the results of a longitudinal study of the development of coordination patterns for this task and on the effect of changing an environmental constraint on the manifestation of that coordination. Five female infants who were just beginning to independently stand up from a seat were studied over 18 weeks. The infants used two relatively distinct patterns of movement to complete the task. The dominant pattern differed across weeks of development and between two seat heights. Relative differences in the contributions of the shank and trunk to the momentum of the body's center of mass, and differences in relative timing between the peak momenta of the shank, thigh and trunk, were shown to differentiate between the two movement patterns. Kinematic relative timing variables were also analyzed, but only the relative onset of knee extension with respect to the trunk cycle clearly distinguished between the two movement patterns. Further studies are needed to assess the roles of various factors (e.g., learning, muscle strength, mass distribution changes) in the performance of this task during development. (C) 2000 Elsevier Science B.V. All rights reserved. PsycINFO classification: 23301; 2221.