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A conceptual model to assess musculoskeletal stress of manual work for establishment of quantitative guidelines to prevent hand and wrist cumulative trauma disorders (CTDs).

Tanaka S; McGlothlin JD
Advances in industrial ergonomics and safety I. Mital A, ed., Philadelphia PA: Taylor and Francis, 1989 Jan; 1:419-426
A conceptual model intended to serve as a prototype for developing guidelines for preventing wrist tenosynovitis was described. The model was developed by assuming that flexion at the wrist reduced the carpal tunnel size, and tensions applied to the flexor tendons during wrist flexion significantly increased pressure in the carpal tunnel. A physiological limit for synovial lubrication of tendon sheaths, which permit smooth gliding of the tendons, was postulated to exist. If this limit was exceeded as a result of forceful movements of the hand and fingers, this could trigger an inflammatory response in the affected tendon sheath unit. It was assumed that friction between the tendon and tendon sheaths in the carpal tunnel was the major factor responsible for aggravating tenosynovitis regardless of the type of grip or task performed by the hands and fingers. The frictional energy produced was proportional to the hand workload, frequency of the movements, and wrist angle. An equation that expressed the action limit and maximum permissible limit for a manual task as the product of the average hand and finger workload needed to complete the task (WL), the repetitiveness of the task cycle per unit time, an exponential term incorporating the wrist angle required for the task, and a constant related to the degree of protection desired was derived. The theoretical upper limit of the WL could be determined by measuring the largest force that could be exerted safely by the hand and fingers and the distance of tendon slide during the task. Suggestions for industrial surveys that could test the model were presented. The authors conclude that the model if validated could be used to evaluate the effectiveness of ergonomic interventions, provide engineers with quantitative ergonomic guidelines when planning the construction of factories, and to explain the principles of manual work stressors to managers, workers, or supervisors.
Biomechanics; Mathematical-models; Work-capacity; Musculoskeletal-system; Carpal-tunnel-syndrome; Ergonomics; Physical-stress; Cumulative-trauma-disorders
Publication Date
Document Type
Conference/Symposia Proceedings
Mital A
Fiscal Year
NIOSH Division
Source Name
Advances in industrial ergonomics and safety I. Proceedings of the Annual International Industrial Ergonomics and Safety Conference held in Cincinnati, Ohio, U.S.A., 5-9 June 1989. The Official Conference of the International Foundation for Industrial Ergonomics and Safety Research
Page last reviewed: May 5, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division