A KINEMATIC COMPARISON BETWEEN ELDERLY AND YOUNG SUBJECTS STANDING UPFROM 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) a nd to determine whether there are age-related differences upon movemen t kinematics in healthy elderly persons during the whole sequence (sta nding up and sitting down). Methods: the movements of various parts of the body were measured with a 100 Hz television image analyser that c omputed the co-ordinates of small reflective markers glued onto the sk in 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 spee d in the dark. Type of study: laboratory study. Results: in young subj ects, 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, th e time required to achieve the movement was found to be greater in sit ting down than in standing up, and an adjustment of velocity appeared in final part of the movement before reaching the chair. In sitting do wn, as in carrying out a pointing task of upper limb, an adjustment wa s required to achieve accuracy. This feature was not found in standing up. Age-related differences appeared to be more important during sitt ing down than during standing up. Moreover, deterioration of head stab ility was found in elderly subjects, particularly when the task was ac hieved rapidly and in darkness. Conclusion: there is a relationship be tween changes in the motor control of the task, which appeared during periods of potential postural instability, and the effects of ageing o n postural stability.