Standing steadiness measurements: empirical selection of testing protocol and outcome measures

A variety of methods for measuring the effects of neurotoxic exposure have been developed and applied in epidemiologic studies of exposed workers. Although impairment of equilibrium is a common complaint among workers exposed to neurotoxicants, only a few studies have been published in which quantitative measurement of standing steadiness was used to assess occupational neurotoxicity. Possible reasons for limited use of these measures include inadequate evaluation and validation of testing protocols. The current project was undertaken to address some of these issues. Specifically, two studies of normal subjects were undertaken a) to compare standing steadiness measurements made with feet together or feet apart, and b) to assess the reliability of a number of potential summary measures for estimating standing steadiness. Study 1 was performed on eight subjects tested on 2 consecutive days. It demonstrated that a) a feet-together position resulted in greater systematic variance than a feet-apart position, b) sway varied systematically within 60-s trials, c) three 60-s eyes-open/eyes-closed trial pairs did not appear to provide more information than two pairs of trials. In Study 2, 30 subjects were tested on two occasions separated by 2 to 7 days using the procedure selected on the basis of the results from Study 1. Overall, the most reliable of several summary measures of standing steadiness was observed to be speed of sway.