10.7 Limitations of joint exertion as a sole risk indicator

Joint-exertion analysis estimates the biomechanical demand required to maintain a posture, balance external loads, or perform an activity represented by a posture sequence. However, its results should not be interpreted as a complete ergonomic risk assessment. Joint exertion is a relevant dimension of the analysis, but it does not account for every mechanism through which a posture or task may adversely affect the musculoskeletal system.

Joint moments, % Recommended Joint Capacity, % Maximum Recommended Exertion, % Maximum Isometric Capacity Used, % Unprotected Population, and cumulative exertion load provide different perspectives on biomechanical demand. None of these indicators alone expresses the probability of injury or a musculoskeletal disorder.

A task may also be unfavorable because of extreme or sustained postures, loading of passive structures, localized tissue compression, surface contact, instability, repetitive low-amplitude movements, vibration, environmental conditions, work organization, or the individual's characteristics.

Exertion-analysis results should therefore be interpreted together with the other available ergonomic indicators, technical observation of the activity, and the actual conditions under which the work is performed.