The biomechanical approach to manual lifting tasks has attempted to estimate worker capacity based on stresses imposed on the musculoskeletal system of the worker. The physiological approach estimates capacity by assessing metabolic energy expenditure. The psychological approach estimates capacity based on subjective evaluation of effort under different job conditions. The principle of psychophysics uses the human capability to judge the subjectively perceived strain at work in order to determine voluntarily accepted work stresses. The industrial task must be simulated as realistically as possible. Factors which affect lifting tasks included factors related to the individual, to the task, to the material being lifted, to the container, and to various environmental conditions. Psychophysical design criteria discussed include the lifting capacity data base, the Liberty Mutual Data Base, the Texas Tech Data Base, the comprehensive data base, and models to predict lifting capacity. The relationship between lifting strength and capacity was considered, specifically lifting strength and lifting capacity, and muscle strength, isometric strength, isokinetic strength, isoinertial strength, and static and dynamic strength. Advantages and disadvantages of the psychophysical approach were discussed.