To know fatigue, we have to analyze the factors and circumstances that have an effect on it. There are many types and places of occurrence of fatigue with many observations and analyzing methods belonging to it.
At all types, the exposure and the alternation of work-break times have a great effect on the level of fatigue. Just as work intensity and the length of work hours. When monitoring fatigue, it should be considered that sleepiness has a negative influence on productivity values (Ashsberg et al. 2000).
If the shift is refracted by shorter breaks instead of one longer that gives more possibilities for regeneration. The number and lengths of breaks are very important, but the breaks actively spent have an even better effect on the regeneration process of the employee. Rotation between tasks and the changes of task content also has a positive effect. (Lunger et al., 2014).
When shifts overstep 8 hours, load cumulates and with the rising level of fatigue the level work-standards can be kept only with greater investment of energy. The level of fatigue increases exponentially from the 8th hour of work, but after the 10th hour, it leads to a decrease in productivity (Wirtz,2009). As the workdays are very long the human body does not have enough time to regenerate before the next shift starts. The human is not capable of tolerating overexertion for a long time so different diseases and problems will evolve in the body. Weekly 5 days and 40 hours should be a maximum to count on to preserve employee health. (Ashsberg et al. 2000, Gemma et al., 2016).
For assessing physical load often questionnaire-type methods are used. In research, work activity-specific methods are coupled to the Sleepiness Scales. These are proven, scale-based methods like the Karolinska Sleepiness Scale or the Stanford Sleepiness Scale. Often the two types of methods give results together. For long-term exposure, the feeling of fatigue is typical while monotony goes hand in hand with sleepiness. (Ashsberg et al. 2000).
In some cases, physical fatigue is analyzed based on muscle contraction, the cycle time of the task, and the ratio of the previous two. The aim is to describe a kind of toughness for defining the time and level of exposure that leads to a fall in productivity. (Iridiastadi and Nussbaum, 2007) Though it is important to know that examinations of physical fatigue have a well-defined scope, characteristically focusing on a body part or region equipped with EMG. In some cases, after reference measurements, EMG results may show fatigue, regeneration, the rise or decline of force. The results can be categorized only in the case of the equipped body part and cannot be spread out to the whole body. To understand EMG signs well, great practice is needed.
Physical fatigue is assessed in a work situation, but not entirely since the analysis itself needs to be provided with reference measures. Therefore, the measurement of muscle fatigue is impossible in work circumstances. On-site measurements supplemented with the reference measures obstruct the analyses of complete motion sequences. Since muscle fatigue is affected by the way of movements and the previous and following movements as well stopping for reference measures hinders punctuality. Using Borg-scale for assessing fatigue or exposure is widely spread. This subjective method is often used for making slight differences and a better understanding of the results of ergonomic risk values. The answers are proven to correlate with the changes of physiological factors (eg.: the pace of heartbeat).
In some cases, risk results are calculated based on the postures taken, their frequency, and the Borg-scale values given, like in Muscle Fatigue Analysis (MFA) method. Another similar method was developed for evaluating the level of inconvenience, it is called BDP (Body Part Discomfort) (Lunger et al., 2014).
Ashsberg, E., Kecklund, G., Akerstedt, T., Gamberale, F., 2000. Shiftwork and di!erent dimensions of fatigue, International Journal of Industrial Ergonomics 26, 457-465.
Caruso, C., Hitchcoock, E.M., Dick, R.B., Russo, J.M., Schmit, J.M., 2004. Overtime and Extended Work Shifts: Recent Findings on Illnesses, Injuries, and Health Behaviors. NIOSH- National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2004-143
Gemma, J.R., Salmon, P.M., Lenné, M.G., 2016. When paradigms collide at the road rail interface: evaluation of a sociotechnical systems theory design toolkit for cognitive work analysis, Ergonomics (59) 9:11, 35-57.
Iridiastadi, H., Nussbaum, M. A., 2007. Muscle fatigue and endurance during repetitive intermittent static efforts: development of prediction models, Ergonomics, 49:4, 344-360.
Keyson, D.V., 2000. Estimation of virtually perceived length. Presence: Teleoperators & Virtual Environments 9 (4), 394-398.
Lunger, T., Bosch, T., Veeger, D., de Looze, M., 2014. The influence of task variation on manifestation of fatigue is ambiguous – a literature review, Ergonomics, Vol. 57, No. 2, 162–174
Ma, L., Chablat, D., Bennis, F., Zhang, W., 2009a. A new simple dynamic fatigue muscle model and its validation. International Journal of Industrial Ergonomics 39 (1), 211-220.
Witmer, B.G., Kline, P.B., 1998. Judging perceived and traversed distance in virtual environments. Presence: Teleoperators & Virtual Environments 7 (2), 144e167.
Wirtz, A., Nachreiner, F., Beermann, B., Brenscheidt, F., Siefer, A., 2009. Lange Arbeitszeiten und Gesundheit, https://www.baua.de/DE/Angebote/Publikationen/Fokus/artikel20.html