A kinematic comparison between elderly and young subjects standing up from and sitting down in a chair.

BACKGROUND AND AIMS The transfer from sitting to standing and back to sitting as the two phases of the same task has never been studied in elderly people. The purposes of this study were to analyse and compare kinematic features of the whole task (standing up and sitting down) and to determine whether there are age-related differences upon movement kinematics in healthy elderly persons during the whole sequence (standing up and sitting down). METHODS The movements of various parts of the body were measured with a 100 Hz television image analyser that computed the co-ordinates of small reflective markers glued onto the skin of the subjects. The task was conducted using an armless chair set to 100% of knee height under four conditions: at normal speed in light, at normal speed in the dark, at fast speed in light and at fast speed in the dark. TYPE OF STUDY Laboratory study. RESULTS In young subjects, the task was characterized by similar acromion trajectories and angular displacement of trunk in standing up and sitting down and by a stabilization of the head in space during the two phases. However, the time required to achieve the movement was found to be greater in sitting down than in standing up, and an adjustment of velocity appeared in final part of the movement before reaching the chair. In sitting down, as in carrying out a pointing task of upper limb, an adjustment was required to achieve accuracy. This feature was not found in standing up. Age-related differences appeared to be more important during sitting down than during standing up. Moreover, deterioration of head stability was found in elderly subjects, particularly when the task was achieved rapidly and in darkness. CONCLUSION There is a relationship between changes in the motor control of the task, which appeared during periods of potential postural instability, and the effects of ageing on postural stability.