A new approach to measure stability during quiet standing

Stability during standing is achieved by a complex process which involves the performance of various systems. Using a force plate for analysing the stability for a period of one minute has been reported exclusively by many investigators. Most of people stand for a long period of time when chatting with somebody, doing a job and when waiting in a queue. However nobody has analysed the stability during quiet standing for a prolonged standing (5 minutes).

The main aim of this research study was to analyse the performance of the subjects regarding stability for a period of 5 minutes.

A group of 40 normal subjects from the staff and students of Rehabilitation Faculty of Isfahan University of Medical Sciences were recruited in this research project. They were asked to stand on the force plate (Kistler) for a period of 5 minutes. They were instructed to look straight ahead and with their head erect and their arms at their sides in a comfortable position. The excursions of the COP sway in both planes were measured for all 20 seconds periods of data collection.

The results of this research study showed that stability analysing based on the sway of the COP, while the test was collected for one minute, is not recommended. There is a significant difference between the excursions of the COP during the first to fifth minutes. The stability of the subject was optimum in the third and fourth minutes of standing.

Using the COP sway, based on the first minute of standing, is neither a good representative of the more stable position nor the unstable position. It is recommended to discuss the stability of subjects based on their ability to return from an unstable position to a more stable position.