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This paper proposes a formulation method on comprehensive evaluation of plural muscle load by applying the methodology of multi-objective optimization. Muscle loads are formulated as objective functions that should be minimized, and comprehensive evaluation of muscle loads is formulated as a multi-objective optimization problem. Design of handrail position for sit-to-stand movement was used as the case study of the proposed method. The height and distance of handrail are design variable, and surface electromyography of anterior deltoid, triceps brachii, rectus femoris, and tibialis anterior were measured when participants stood from a chair with handrails. The ratio of the maximum voluntary contraction (MVC) was used as the indicator of muscle loads. Result from the measurement, it is found that the muscle loads of triceps brachii and tibialis anterior have trade-off relationship on the assumption that %MVC indicates the muscle loads. The higher and the closer the position of handrail is, the higher the muscle load of triceps brachii is, conversely, the lower the muscle load of tibialis anterior is. The two muscle loads were approximated as quadratic functions, and formulated as a multi-objective optimization problem. The optimization problem was solved by the satisficing trade-off method, and the Pareto optimal solution for the participants was obtained at which the height is 234 mm and the distance is 585 mm. The comprehensive evaluation of the two muscle loads probably expresses the sense of the participants more precisely than the use of either of the two muscles.

Fundamental Study on Ergonomic Design Method Based on Comprehensive Evaluation of Muscle Load Using Surface Electromyography