Human Workload

Physical and mental stress is the total of all assessable influences impinging upon a human being from external sources and affecting that person physically and mentally.

Physical and mental strain is the immediate effect of physical and mental stress within the individual; with their current condition potentially having a moderating effect.

Work stress and work strain are crucial for assessments of work systems design quality. Multidimensional measurement and differentiation with regard to type, level and dynamics of work stress may be required.

Work stress (physical and mental) is synonymously used with the term external workload. The figure illustrates the stress-strain relationship.


  • EN ISO 10075-1:2017. Ergonomic principles related to mental workload - Part 1: General issues and concepts, terms and definitions. Brussels: CEN
  • Hacker (2011). Mental workload. In: Stellmann, J.M. (ed.) ILO Encyclopaedia of Occupational Health and Safety (vol. 1, 29.41-43). International Labour Office (ILO), Geneva.