Age-related differences in body segmental movement during perturbed stance in humans

OBJECTIVE: The temporal and spatial features of body segmental movements of the head, trunk, thigh, shank and foot in response to a fast speed postural disturbance were compared among four age groups. It was hypothesized that the upper body movement was minimized in the healthy young adults, but was augmented in the older adults. DESIGN: Repeated measures design with 12 experimental conditions. BACKGROUND: It is not well understood yet why the elderly fall more than the young. In studies of locomotion and active balance tasks, the head position has been suggested as a reference frame for controlling dynamic equilibrium. This study was aimed at examining: (1) whether or not this reference frame would exist during involuntary balance tasks, which are most likely related to accidental falls in the elderly; and (2) how would the stability of this reference frame change with age. METHODS: Thirty-six healthy subjects of four age groups (20-70 + yr of age) participated in this study. Postural perturbation was introduced by a moving platform. The sagittal plane kinematics of five body segments was directly measured using Integrated Kinematic Sensors. RESULTS: Compared to the lower limb movement, the upper body movement, especially the head, was minimal (less than 7 degrees ) in the young adults (age group 1), and was largest (about 14 degrees ) in the older subjects (age groups 2, 3 and 4). Moreover, the maximum range of motion of the older adults was found to be positively correlated not only to the height of the segment, but also to the timings of the movements, while the young adults showed no correlation between range of motion and the timings of the movement. CONCLUSIONS: The findings suggested that the young adults indeed stabilized their upper body as a reference frame for maintaining postural balance. In contrast, this reference frame was not stabilized well in the older adults. In compensation, the older adults adopted a more rigid movement strategy, compared to a more flexible movement strategy in the young. All these changes would lead the older subjects to be less tolerable to postural disturbances and more susceptible to falls than the young subjects.