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

The task of standing up from sitting requires coordinated movements of mult iple body segments. This article presents the results of a longitudinal stu dy of the development of coordination patterns for this task and on the eff ect of changing an environmental constraint on the manifestation of that co ordination. Five female infants who were just beginning to independently st and up from a seat were studied over 18 weeks. The infants used two relativ ely distinct patterns of movement to complete the task. The dominant patter n differed across weeks of development and between two seat heights. Relati ve 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 th e peak momenta of the shank, thigh and trunk, were shown to differentiate b etween the two movement patterns. Kinematic relative timing variables were also analyzed, but only the relative onset of knee extension with respect t o the trunk cycle clearly distinguished between the two movement patterns. Further studies are needed to assess the roles of various factors (e.g., le arning, muscle strength, mass distribution changes) in the performance of t his task during development. (C) 2000 Elsevier Science B.V. All rights rese rved. PsycINFO classification: 23301; 2221.