Mental fatigue is defined as a “state of reduced mental alertness that impairs performance”. It is believed to exist in the nervous system and affect the mental activities of people, such as the motivation and attention. It often occurs when working on cognitively demanding tasks for a prolonged period of time and causes difficulties for people in maintaining task performance at an adequate level. Furthermore, in some cases, mental fatigue can lead to vital consequences for people, such as drivers, pilots and surgeons.
Mental fatigue is also a contributing factor for some medical conditions, such as cardiovascular diseases, hypothyroidism, and fibromyalgia. Therefore, it is of great importance to find out the mechanism and the assessment of mental fatigue. However, the level of mental fatigue is difficult to identify. Usually, mental fatigue is detected by significant change of fatigue indices.
Physical activities usually come with physical fatigue. Physical fatigue (or muscle fatigue) is another kind of fatigue which is caused by physical activities and defined as the inability to maintain a required force level after prolonged use of muscle. It is a complex, multifactorial phenomenon influenced by the characteristics of the task being performed. Physical fatigue is believed to be developed gradually soon after the onset of the sustained physical activity