Exposure Assessment of Biomechanical Stress in Repetitive Manual Work Using Spectral Analysis

Abstract

Theory for a quantitative exposure assessment strategy is presented for measuring physical stress associated with manual tasks containing repetitive motion, postural stress, and forceful exertions. Physical stress is measured directly using electrogoniometers for articular motion, and sensors or electromyography are used for assessing forceful exertions. A method is described for reducing the large quantities of biomechanical data that can be recorded for repetitive manual work into quantifiable metrics based on recognized exposure factors, including repetitiveness, postural stress, forcefulness, and duration. A frequency domain approach is used for averaging elemental data from repetitive cycles. This paper shows how parameters for frequency-weighted filters may be developed from psychophysical data for equivalent discomfort levels. Low force repetitive wrist flexion was used as an example of the feasibility for implementing this approach. Applications of this theory include assessing exposure to physical stress in a manner analogous to the way sound level meters are used for measuring exposure to acoustic noise. A suitable data reduction method is necessary for conducting large scale detailed epidemiological investigations of cumulative trauma disorder risk factors. Development of frequency-weighted filters based on human response to stress at different frequencies may make it possible to establish quantitative exposure limits.