Physiological basis of fatigue (original) (raw)
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Annales de Réadaptation et de Médecine Physique, 2006
Although everyone knows fatigue personally, it is a difficult concept to define. For muscular fatigue, one must know the aspect of performance affected. The most obvious demonstrations are decreased maximal force and slowed muscular answer. Fatigue can have a central origin, by reducing cognitive performance or lowering excitation of motoneurons. Various mediators are in question (serotonin, moduline, dopamine). The fatiguing muscular contractions are accompanied by reduced discharges of motoneurons. The neuromuscular junction does not seem to be in question. Cold reduces muscular power, whereas a hot environment limits exercise by a central mechanism, which starts the normal behavioural response to stop the exercise. Fatigue can also be the consequence of overtraining. In the periphery, the electric activity of the membrane's surface is the first possible sign of failure, which explains high-frequency fatigue: the accumulation of potassium outside the cell blocks the sodic channels to block the potentials of action or slow down their propagation. With fatigue, less calcium is released and limits the number of attached actin-myosin bridges connections of actin-myosin. The slowing down of the muscular answer represents a deterioration of the function of actin-myosin bridges. On the metabolic level, the most-often evoked changes are reduced pH and increased intracellular lactate level. However, these variations cannot all describe fatigue, since patients with Mc Ardle disease do not exhibit these variations but very quickly experience tiredness. In fact, an association of small metabolic intracellular variations could explain tiredness. The fast fibres are larger than slow fibres; their metabolic needs are higher and they are thus more sensitive to tiredness. The half time of recovery is within approximately 1 min: normal values of force and power are recovered after 5 to 10 min. During endurance activities, the limiting factors are glycogen reserves and levels of oxidative enzymes. On the whole, mechanisms of fatigue must be explored to completely understand the governing phenomena.
The Effects of Exercise-Training on the Development of Fatigue
Annals of the New York Academy of Sciences, 1977
An increase in endurance is synonymous with a postponement of the development of fatigue. A thorough understanding of the mechanisms by which endurance is increased by exercise-training is therefore dependent on an elucidation of the mechanisms responsible for fatigue. Despite considerable interest in this area, relatively little is known regarding the biochemical events that result in the various symptoms that can force an individual to stop exercising because of fatigue. One point seems clear, however, and that is that fatigue or exhaustion can have various etiologies depending on the intensity and duration of the exercise, the environmental factors, and the individual's condition.
Metabolic and hormonal basis of fatigue during exercise
European Journal of Experimental Biology, 2013
Exercise-induced reduction in maximal force production or the inability to continue activity with enough force is defined as fatigue. Although the etiology of fatigue is complex, but it can be divided into two distinct parts: Central and peripheral which are not separated from each other and have close relationship with each other. Different activities cause fatigue and main challenge is identifying the different mechanisms which are involved in various conditions. Seemingly the traditional justification of the intra cellular accumulation of lactic and hydrogen ions, which cause to dysfunction of contractile protein in mammals, particularly humans, has little significance. In one hand most of the studies about fatigue has been done on isolated animal fiber and in another hand the main issue is putting the dispersed information from different studies together in order to understand the fatigue mechanism in human, particularly athletes. Topics which will be discussed in this study would complete our understanding of the metabolic and hormonal fatigue. _____________________________________________________________________________________________ Sporting activities are accompanied by the changes in metabolite levels in which the magnitude of the changes depends on the type of activity. For example, activities with working load more than the critical power results to
American family physician, 2008
Fatigue, a common presenting symptom in primary care, negatively impacts work performance, family life, and social relationships. The differential diagnosis of fatigue includes lifestyle issues, physical conditions, mental disorders, and treatment side effects. Fatigue can be classified as secondary to other medical conditions, physiologic, or chronic. The history and physical examination should focus on identifying common secondary causes (e.g., medications, anemia, pregnancy) and life-threatening problems, such as cancer. Results of laboratory studies affect management in only 5 percent of patients, and if initial results are normal, repeat testing is generally not indicated. Treatment of all types of fatigue should include a structured plan for regular physical activity that consists of stretching and aerobic exercise, such as walking. Caffeine and modafinil may be useful for episodic situations requiring alertness. Short naps are proven performance enhancers. Selective serotonin...
The journal of supportive oncology
Fatigue is a common experience of individuals suffering from chronic illnesses. Mechanisms responsible for fatigue may be central or peripheral. Central fatigue may result from proximal events and include the neuromuscular junction and are subdivided into spinal and supraspinal. Peripheral fatigue arises from the muscle and predominately involves muscle bioenergetics or excitation contraction. Fatigue from chronic illnesses can be caused by several mechanisms. Electromyelography, transcranial magnetic stimulation, magnetic resonance imaging, and spectroscopy are helpful tools to clarify the physiologic correlates of fatigue. This state-of-the-art review discusses these physiologic correlates of fatigue and the mechanisms described in a variety of chronic diseases.
International Journal of Occupational Medicine and Environmental Health, 2008
Objectives: Complaints of prolonged fatigue are considered as a major health problem, as it can affect daily functioning and may lead to work disability. To increase knowledge about the effectiveness of interventions focussing on fatigued patients, a study was designed to evaluate an established training programme for patients with prolonged fatigue. Materials and Methods: Eighteen patients who reported fatigue to be one of their major health complaints and who were suffering from functional impairments attended a training programme of six weeks, three times a week. The training consisted mainly of physical endurance training, relaxation therapy and breathing exercises in rest. At baseline, time-and frequencydomain measures of heart rate variability (HRV) and respiration rate measurements were recorded during rest and during recovery after bicycle exercise. Furthermore, fatigue complaints were assessed with the Checklist Individual Strength (CIS). These measurements were repeated at three weeks and six weeks from baseline. Results: After three weeks, HRV increased significantly in rest-SDNN, i.e. standard deviation of normal beat-to-beat intervals (p = 0.02), very low frequency (p = 0.04) and low frequency (p = 0.04)-and showed a positive trend in the remaining HRV components. No significant HRV changes during recovery were found. Respiration rate decreased significantly after six weeks during rest (from 11.8, SD = 4.65 to 8.1, SD = 2.57 b×min-1) and during recovery (from 15.1, SD = 4.90 to 10.4, SD = 2.97 b×min-1). In all patients, CIS scores decreased after six weeks training (from 106, SD = 13.3 to 78, SD = 21.8, p = 0.001). Conclusions: The results suggest that a six-week training programme has a beneficial effect on physiological and subjective parameters in patients with severe complaints of fatigue.