Perceived fatigue at work is important because it may be unpleasant for the individual, it may interfere with productivity, and prolonged fatigue without recovery may lead to work-related disorders. This thesis presents a comprehensive approach towards assessment of work-related perceived fatigue. The thesis is based on the notion that perceived fatigue is a multi-dimensional construct, and the principal aim is to identify these dimensions. The aim is further to develop an instrument for measuring work-related perceived fatigue based on self-reports, and to validate the importance of these fatigue dimensions during different types of work. An instrument, the Swedish Occupational Fatigue Inventory (SOFI), was developed for measuring fatigue based on self-reports. In a questionnaire survey 705 employees from different occupations described their perceived fatigue by rating 95 verbal expressions. Factor analyses resulted in five dimensions of work-related perceived fatigue. These dimensions were called Lack of energy, Physical exertion, Physical discomfort, Lack of motivation, and Sleepiness. The SOFI consisted of 25 items, and each of the five dimensions were assessed by five items.
The proposed five-dimensional model of perceived fatigue was evaluated in two laboratory experiments and one field study. The first experiment focused on fatigue after physical work, whereas the second experiment focused on fatigue after mental work. The field study was conducted among industrial three-shift workers, who answered a questionnaire after each shift. The results indicated a reasonably good validity of the instrument, in the sense that it showed an ability to reflect different fatigue dimensions in different types of work. That is, perceived fatigue due to physical work was primarily described by Lack of energy, Physical exertion and Physical discomfort, fatigue due to mental work primarily by Lack of energy, Lack of motivation and Sleepiness, and fatigue due to night work primarily by Sleepiness. The results also add to previous knowledge by showing that night work is not only associated with perceived Sleepiness, but also with Lack of energy and Lack of motivation.
The proposed five-dimensional model of perceived fatigue was cross-validated in a new occupational population, using the SOFI to assess fatigue in different work situations. Linear structural equation analyses (LISREL) of the results suggested a slightly revised model for perceived fatigue, still comprising five dimensions, but with a reduced number of variables - 20 instead of 25. Lack of energy was defined as a latent factor directly related to all observed variables, indicating its general character.
The results in this thesis also showed common gender differences of perceived fatigue in field settings: women reported more fatigue than men. However, gender did not differ in fatigue during simulated work in the laboratory, irrespective of whether the work consisted of similar mental workload or individually adjusted physical workload. This indicates that work-related perceived fatigue is influenced by factors other than the work task.
In conclusion, work-related perceived fatigue can be described as being composed of five dimensions. An instrument, the SOFI, has been developed. The results indicated a reasonably good validity for the SOFI.
Stockholm: National Institute for Working Life (Arbetslivsinstitutet) , 1998. , 32 p.