by Fatigue is a feeling of tiredness. It may be sudden or gradual in onset. It is a normal phenomenon if it follows prolonged physical or mental activity, and resolves completely with rest. However, it may be a symptom of a medical condition if it is prolonged, severe, progressive, or occurs without provocation.
Physical fatigue is the transient inability of muscles to maintain optimal physical performance, and is made more severe by intense physical exercise. Mental fatigue is a transient decrease in maximal cognitive performance resulting from prolonged periods of cognitive activity. Mental fatigue can manifest as somnolence, lethargy, or directed attention fatigue.
Fatigue and ‘feelings of fatigue’ are sometimes confused. Unlike weakness, fatigue usually can be alleviated by periods of rest.
Fatigue is often described as a lack of energy and motivation both physical and emotional. It is different than sleepiness or drowsiness, which describe the need for sleep. Fatigue is also a response to physical and mental activities. Normally, fatigue can be resolved with rest or reducing activity. Fatigue is a common complaint related to health issues. Notably, it is a symptom and not a specific disease or health condition. Many illnesses cause fatigue, and the symptoms can be physical, psychological, or a combination of both.
Physical fatigue
Physical fatigue, or muscle fatigue, is the temporary physical inability of muscles to perform optimally. The onset of muscle fatigue during physical activity is gradual, and depends upon an individual’s level of physical fitness other factors include sleep deprivation and overall health. Fatigue can be reversed by rest. Physical fatigue can be caused by a lack of energy in the muscle, by a decrease of the efficiency of the neuromuscular junction or by a reduction of the drive originating from the central nervous system. The central component of fatigue is triggered by an increase of the level of serotonin in the central nervous system. During motor activity, serotonin released in synapses that contact motoneurons promotes muscle contraction. During high level of motor activity, the amount of serotonin released increases and a spillover occurs. Serotonin binds to extrasynaptic receptors located on the axon initial segment of motoneurons with the result that nerve impulse initiation and thereby muscle contraction are inhibited.
Muscle strength testing can be used to determine the presence of a neuromuscular disease, but cannot determine its cause. Additional testing, such as electromyography, can provide diagnostic information, but information gained from muscle strength testing alone is not enough to diagnose most neuromuscular disorders.
People with multiple sclerosis experience a form of overwhelming lassitude or tiredness that can occur at any time of the day, for any duration, and that does not necessarily recur in a recognizable pattern for any given patient, referred to as “neurological fatigue”.
Mental fatigue
Mental fatigue is a temporary inability to maintain optimal cognitive performance. The onset of mental fatigue during any cognitive activity is gradual, and depends upon an individual’s cognitive ability, and also upon other factors, such as sleep deprivation and overall health. Mental fatigue has also been shown to decrease physical performance. It can manifest as somnolence, lethargy, or directed attention fatigue. Decreased attention may also be described as a more or less decreased level of consciousness. In any case, this can be dangerous when performing tasks that require constant concentration, such as operating large vehicles. For instance, a person who is sufficiently somnolent may experience microsleep. However, objective cognitive testing can be used to differentiate the neurocognitive deficits of brain disease from those attributable to tiredness.
The perception of mental fatigue is believed to be modulated by the brain’s reticular activating system (RAS).
Fatigue impacts a driver’s reaction time, awareness of hazards around them and their attention. Drowsy drivers are three times more likely to be involved in a car crash and if they are awake over 20 hours, is the equivalent of driving with a blood-alcohol concentration level of 0.08%.
Symptoms
According to a 2019 report in the journal Biological Research for Nursing, fatigue can be defined as an “overwhelming, debilitating, and sustained” exhaustion that makes it harder to carry out activities and function. Family practice physicians report that at least 20% of their patients report fatigue and up to 35% of adolescents report fatigue that occurs at least four days a week.
Men and women will describe fatigue differently. For example, men may say they are feeling tired, whereas women may report their fatigue as a feeling of anxiety or depression. People may also describe fatigue using a variety of terms, including feeling exhausted, weary, listless, or rundown.
People with fatigue experience one or more of three primary complaints. These vary person-to-person. They are:
- Lack of motivation or the ability to start activities
- Getting tired easily
- Experiencing mental fatigue or problems with concentration or memory
Often, fatigue is a symptom with a gradual onset, meaning it comes on slowly and gets worse with time. Most people who experience fatigue may not be aware early on how much energy they are losing. They can only determine this when they try to compare their ability to perform tasks from one-time frame to another.
Further, they may think fatigue is a common symptom due to aging, being busy or overworked, not getting enough sleep, or a combination of all of these and ignore the symptom.
Causes
Normal
Fatigue is a normal result of working, mental stress, overstimulation and under stimulation, jet lag, active recreation, boredom, and lack of sleep.
Acute
Causes of acute fatigue include depression; chemical causes, such as dehydration, poisoning, low blood sugar, or mineral or vitamin deficiencies. Fatigue is different from drowsiness, where a patient feels that sleep is required.
Temporary fatigue is likely to be a minor illness like the common cold as one part of the sickness behavior response that happens when the immune system fights an infection.
Prolonged
Prolonged fatigue is a self-reported, persistent (constant) fatigue lasting at least one month.
Chronic
Chronic fatigue is a self-reported fatigue lasting at least six consecutive months. Chronic fatigue may be either persistent or relapsing. Chronic fatigue is a symptom of many diseases and conditions.
