Repetitive work of the upper extremity: Part II — The scientific basis (knowledge base) for the guide

The concept "repetitive work" refers to similar work tasks performed again and again. By necessity, repetitive work of the upper extremity implies a motor component, which can be defined in terms of time and force. Repetitive work of the upper extremity is considered one of several physical work load factors, associated with symptoms and injuries of the musculoskeletal system. Other important factors are static loads, postures, and exertion of external forces. Scientific literature does not yet provide sufficient support for a separate assessment of risk for each one of these factors. They occur simultaneously or during alternating tasks within the same occupational work, and their effects concur and interact. Usually, harmful effects on the musculoskeletal system cannot be identified separately for each factor. Thus neither epidemiological, clinical or physiological/biomechanical studies support the view that repetitive work should be considered the prime exposure factor, without simultaneous consideration of forces and postures. Physical exposures should therefore be described and quantified with composite measures that consider all these factors (Drury, 1987; Putz-Anderson, 1988; Wells et al., 1989). In such exposure measures duration of exposure (hours, days, years) should also be included. For a complete risk assessment the characteristics of the individual and psychological and social conditions at work should also