Inter-segmental co-ordination in sit-to-stand: an age cross-sectional study

Being able to sit-to-stand (STS) effectively is an important functional skill, but there is little information available on the changes that occur with growth and maturity. This study aimed to investigate the inter-segmental co-ordination of STS in three different age groups (12-18 months, 4-5 years and 9-10 years).

The children studied wore reflective markers and were videotaped as they stood up from a height-adjustable seat that straddled a forceplate. Segmental kinematics and vertical ground reaction force were determined from the co-ordinate and forceplate data.

Even at the earliest developmental stage the children had mastered the basic inter-segmental pattern observed in adults. The youngest children, however, were not able to end the movement in quiet standing; rather they raised up on their toes or took a step forward. Performance varied both within and between subjects. Although there was a similarity in the motor pattern used by the younger subjects to that of the older subjects, developmental trends were evident on the videotapes and on examination of the kinematic and kinetic variables. Movement time, amplitude and peak angular velocity of trunk flexion increased with age. Whereas the children in the older age groups displayed a pattern of vertical ground reaction force similar to that reported for adults, the youngest children tended to reach peak force gradually, often with fluctuations. Although there were characteristic trajectories in the phase-plane plots for each group, the overall trend was for the percentage of smooth plots representing a co-ordinated movement, to increase with age.

Differences in inter-segmental co-ordination between the ages studied may relate to the child's ability to control horizontal momentum and to balance.