Everyone knows the sensations which arise after hours of driving a car or focused working in front of a screen. These sensations can manifest subjectively as feelings of tiredness or even exhaustion and are termed as mental fatigue. Mental fatigue is a psychobiological state induced by sustained periods of demanding cognitive activity and has implications for many aspects of daily life. For example, it has been shown that mental fatigue predicts error rates at the workplace and even impairs endurance performance.
Mental fatigue can be apparent subjectively, behaviorally and physiologically. The subjective dimension includes increased feelings of tiredness and lack of energy as well as decreased motivation and altered mood. Behaviorally, mental fatigue can result in a decline in performance during a cognitive task, e.g. accuracy and reaction time. From a physiological perspective, mental fatigue is associated with alterations in brain activity and adjustments within the autonomic nervous system.
There is growing evidence that impaired cognitive functioning is associated with poor gait performance in healthy older people which is associated with an increased risk of falling. Despite mental fatigue being a potent(ial) contributor to cognitive impairments, its acute effect on gait performance has never been investigated before. Therefore, scientists of the University of Rostock and the University of Greifswald in Germany quantified gait parameters and psychometric measures before and after a 90-minutes lasting mental fatiguing task or a control task in young and old adults.
The mental fatiguing task consisted of a computerized test which required high attention and quick responses while the participants watched a neutral video during the control task. Gait performance was measured during single-task and dual-task walking, i.e. walking only and walking plus an arithmetical task, respectively. Results showed that gait performance was impaired following the mental fatiguing task in the dual-task condition only in old participants. The authors concluded that the susceptibility to mental fatigue might be a new intrinsic risk factor for falls in older people since previous studies have shown that dual-task gait performance is predictive for falls in the elderly.
Furthermore, the extent of mental fatigue should be taken into account when dual-task gait analyses are performed. The relevance of these findings for patient populations, particularly those with neurologic diseases showing a high prevalence and severity of fatigue symptoms, should be analyzed in the future.
The underlying mechanisms for the observed effect include, i.a., age-related structural alterations of the brain, e.g., in the prefrontal areas. This factor has been identified as a contributor to decreased gait performance under dual-task conditions in older people. Challenging these brain areas by means of a mentally fatiguing task seems to impair gait performance during dual-task walking in the old age. Since this effect of mental fatigue on gait performance during dual-task walking was not observed in the younger participants, young adults may cope with the cognitive interference task in a mental fatigued state without attenuating the processing capacity for the motor task.
This synthesis is from the study: Behrens, M., Mau-Moeller, A., Lischke, A., Katlun, F., Gube, M., Zschorlich, V., Skripitz, R., Weippert, M. (2017). Mental fatigue increases gait variability during dual-task walking in old adults. The Journals of Gerontology Series A: Medical Sciences, DOI: 10.1093/gerona/glx210.