Exposure assessment of biomechanical stress in repetitive manual work using frequency-weighted filters

A quantitative exposure assessment strategy for physical stress associated with repetitive manual tasks is proposed using continuous biomechanical data measured directly from electrogoniometers or force sensors. This paper describes an efficient method for reducing large quantities of biomechanical data into a quantifiable metric that accounts for recognized musculoskeletal exposure factors, including repetitiveness, postural or forceful exertion stress, and duration. A frequency domain approach is used for averaging elemental data recorded for repetitive cycles. Parameters for frequency-weighted filters are developed using psychophysical data for equivalent discomfort levels resulting from repetitive movements of different amplitudes and frequencies. These filters enable continuous biomechanical data to be filtered and integrated, resulting in a single quantity corresponding to psychophysical response characteristics for repetitive motion stress. It is anticipated that a similar approach may be used for epidemiological response characteristics. Applications of this theory may make it possible for assessing exposure to physical stress in a manner analogous to the way in which sound level meters are used for measuring exposure to acoustic noise. Repetitive wrist flexion and localized discomfort was used for demonstrating the feasibility of this approach. Suitable data reduction techniques are necessary for evaluating work methods, job designs, and for conducting large scale detailed epidemiological investigations of cumulative trauma disorder risk factors. Frequency-weighted filters based on human response to physical stress at different frequencies can greatly simplify exposure analysis and ultimately may make it possible for quantitative exposure limits to be established.