Postural sway patterns of normal men and women and men with mental retardation during a two-legged stance test

Previous research has shown that in healthy subjects during a quiet two-legged stance, sagittal postural sway is greater than lateral postural sway with a ratio approximating 1.5. The purpose of this study was to examine the postural sway profiles of healthy men and women, and men with mental retardation (MR). Subjects consisted of 22 men (M), 22 women (W) and 22 men with MR. Postural sway characteristics were examined using a Kistler force platform. Each subject performed six trials, three with vision and three with vision occluded. Each trial was 15sec in duration, and the subject was instructed to stand motionless on the force platform. A custom-designed computer program sampled the lateral and sagittal sway characteristics for each trial, at a sample rate of 50Hz. Results indicated that the MR group exhibited significantly more lateral sway than the other two groups, and that the sagittal/lateral sway ratio was significantly lower in this group. Moreover, the MR group showed a greater amount of sway in the no-vision condition than either the M or W groups. Using the sagittal/lateral sway ratio, discriminant analyses indicated that group membership could be predicted in 75% to 82% of the cases in the vision condition, and 64% to 73% of the cases in the no-vision condition. It is concluded that the sagittal/lateral sway ratio provides a valid and objective assessment measure to determine the postural control/balance capacities of persons with MR. In addition, it is hypothesized that this ratio may prove useful in quantifying the effectiveness of therapeutic intervention programs on balance performance.