Differences between young and older adults in the control of weight shifting within the surface of support

Abstract

An important reason for falling in elderly is incorrect weight-shifting. In many daily life activities quick and accurate weight-shifting is needed to maintain balance and to prevent from falling. The present study aims to gain more insight in age-related differences in the control of weight-shifting. Nine healthy older adults (70.3 ± 6.9 years) and twelve young adults (20.9 ± 0.5 years) participated in the study. They performed a weight shifting task by moving the body's center of pressure, represented by a red dot on a screen, in different directions, towards targets of different sizes and at different distances projected on a screen. Movement time, fluency and accuracy of the movement were determined. Accuracy was quantified by the number of times the cursor hit the goal target before a target switch was realized (counts on goal) and by the time required to realize a target switch after the goal target was hit by the cursor for the first time (dwelling time). Fluency was expressed by the maximal deviation of the performed path with respect to the ideal path and the number of peaks, or inflections in the performed path. Significant main effects of target size, target distance and age on all outcome measures were found. With decreasing target size, increasing target distance and increasing age, movement time significantly increased and fluency and accuracy significantly decreased (i.e. increased number of peaks, maximal deviation, number of times on the goal target and longer dwelling time around the goal target). In addition, significant interaction effects of size*age and distance*age were found. Older adults needed more time to perform the weight-shifting task and their movements were less fluent and accurate compared to younger adults, especially with increasing task difficulty. This indicates that elderly might have difficulties with executing an adequate adaptation to a perturbation in daily life.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Experimental Setup.

A person standing on the platform looking at the projection screen in front of him and performing the task by moving the red dot (COP position) to the white target, by shifting his weight as fast and accurate as possible.

Figure 2. Schematic overview of all possible target positions.

The white square is the home target, the grey squares are the goal targets. In reality only one target was visible during the task. The letters W, NW, N, NE and E indicate the different wind directions (west, northwest, north, northeast and east respectively).

Figure 3. Schematic overview of the outcome parameters.

Figure 4. COP trajectories of one block of 45 experimental trials of a young subject (A) and an older subject (B) and COP trajectory of one experimental trial of a young subject (C) and an older subject (D); COP position in x direction is plotted against COP position in y direction.

Figure 5. Mean values for all outcome measures for the young and older adults group (triangles, squares respectively) for the three different target sizes and target distances.

Error bars represent group standard deviations. Averaged over sub values and standard deviations of all outcome measures for each size and distance.