Occupational ergonomics has long focused on physical exertion as a key to the prevention of musculoskeletal injuries. Traditionally, objective measurements of forceful exertion such as electromyography (EMG) and direct force measurement have been used to assess exposure to forceful exertion. However, these measurements are often not practical for occupational settings due to their cumbersome and costly nature. As a result, psychophysical magnitude estimation may be used, in which human subjects verbally estimate the magnitude of an exertion. Despite an abundance of research on verbal estimation, its repeatability and the effects of fatigue on estimation accuracy have not been sufficiently assessed. An understanding of these factors is critical for the successful implementation of verbal estimation in occupational settings. The objectives of this research were to quantify the short and long term repeatability of psychophysical magnitude estimation as well as analyze the effect of fatigue on the accuracy of estimation. Fifteen subjects performed two experiments separated by one week, in which they performed verbal estimation of submaximal forces. In addition to testing for repeatability, subjects were systematically exposed to muscular fatigue to evaluate its effect on accuracy. The results show that verbal estimation is repeatable in both the short and long term for submaximal exertions. In addition, the presence of muscular fatigue was shown to have a detrimental effect on the accuracy of estimation. On average, the estimation accuracy decreased 7.56% MVC in the presence of fatigue.

Library of Congress Subject Headings

Fatigue--Measurement; Human engineering

Publication Date


Document Type


Department, Program, or Center

Industrial and Systems Engineering (KGCOE)


Marshall, Matthew

Advisor/Committee Member

Mozrall, Jacqueline


Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works. Physical copy available through RIT's The Wallace Library at: T59.72 .K56 2007


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