Why do i have Fatigue You feel exhausted. All you want to do is eat something tasty and get a good night’s sleep. You do not have the strength and motivation to even go to work, and a short cross-country race in a nearby park or a workout in the gym seems more than impossible. Clearly, you are tired! But what is fatigue and what are the physiological mechanisms that cause it?
Fatigue is a physiological condition of the body, the result of physical and mental overload, the external expression of which is the reduction or temporary loss of ability to work. Fatigue is a protective reaction of the body, preventing it from overexcitation and depletion of energy and nutrients with a possible fatal outcome.
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Theories of the origin of fatigue
An unambiguous explanation of the physiological preconditions leading to the onset of fatigue is still lacking. In the past, several theories have attempted to explain this physiological phenomenon, but none of them seems entirely plausible:
- Theory of exhaustion – according to her, fatigue is mainly the result of the consumption of energy reserves of the body, without which it is unable to maintain its efficiency.
- Congestion theory – according to this theory, the primary cause of fatigue is the accumulation in the body of metabolic waste products.
- Theory of suffocation – in the foreground is the inability of the body to respond to the increased oxygen needs of working muscles.
Nowadays, it is well known that fatigue is a complex process caused by simultaneous functional changes in the working organs and systems, as well as in the central nervous system. Proof of this are the characteristic changes occurring in them:
- Changes in the central nervous system. Most often, when fatigue occurs, impaired coordination of movements is observed, their accuracy and precision are reduced, their speed and strength in most cases do not correspond to the planned ones.
- Changes in sensory systems. The involvement of the visual and vestibular systems is most pronounced. When fatigue occurs, their sensitivity is greatly reduced, and it is possible to reach a temporary loss of full functionality.
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Muscle change. Fatigue-induced changes in muscle tissue are the result of both depletion of energy reserves and disruption of their nervous regulation. In most cases, there is a decrease in the strength of muscle contractions, as well as muscle excitability.
The occurrence of fatigue, the degree of its severity, the changes it causes in individual organs and in the central nervous system, as well as the time required for recovery, depend on a number of factors. These are gender and age, health status, level of training, type and volume of physical activity.
Causes of fatigue
As already mentioned, fatigue is most likely a consequence of the simultaneous occurrence of a large number of changes in almost all organs and systems of the human body. Here are some of the main reasons for its occurrence:
Depletion of adenosine triphosphate (ATP) and creatine phosphate (CF)
The ATP accumulated in the muscles is an immediate source of energy for their contraction during short-term physical activity with high power. Maintaining this type of muscle work depends on the rate of use and the rate of ATP synthesis. In exercises such as weight lifting, which are strongly anaerobic, the resynthesis of ATP is only at the expense of the available CF.
However, the content of ATP and CF in the muscles is extremely low and can provide energy for muscle work lasting up to about 10 seconds. It has been established that at isometric loads and at those with overmaximum power, the occurrence of fatigue coincides with the depletion of creatine phosphate reserves.
Depletion of muscle and liver glycogen stores
Glycogen is a substrate that is extremely important for the body’s energy supply during physical activity. The speed at which it is expended during physical activity is directly dependent on their intensity. The higher the intensity, the faster glycogen is depleted. The human body can store about 2,000 kcal of energy in the form of glycogen. This means that during prolonged physical activity, its amount can drastically decrease and cause fatigue, bordering on the inability to perform any movements.
Lowering blood sugar
During short-term exercise with high intensity, there is an initial increase in blood sugar levels (hyperglycemia) due to the release of glucose from liver glycogen. However, with prolonged physical exertion, it is expended and the maintenance of blood sugar levels depends mainly on the production of glucose from non-carbohydrate sources (gluconeogenesis).
As a result, blood sugar levels fall, glucose flow to the brain and to working muscles decreases, and performance decreases. If you do not “listen” to the body’s signals and stop training, your blood sugar levels can drop critically and lead to side effects of hypoglycaemia.
Accumulation of lactic acid (lactate)
Lactic acid is a product of anaerobic glycolysis (the breakdown of carbohydrates in the absence of oxygen), which provides energy to physical activity lasting up to about 60 seconds. Lactic acid is strongly acidic (has a low pH) and leads to complete acidification of the body. This prevents normal muscle contractions, can activate some pain receptors and even cause receptor irritation in the brain and subsequently reactions such as disorientation, nausea and vomiting. High amounts of lactate in the blood inhibit lipolysis and prevent the use of fats as an energy source.
Accumulation of calcium in the mitochondria
During prolonged exercise, some of the calcium released during muscle contractions accumulates in the mitochondria. This complicates their normal functioning and reduces their efficiency in the production of ATP.
Disturbance in homeostasis
Prolonged physical activity can cause serious changes in the stability of the internal environment of the body (homeostasis) such as: significant fluid loss, fever, changes in blood properties, etc., which significantly impede the normal functioning of organs and systems and lead to fatigue.
Changes in CNS functions
Although the specific changes that occur in the CNS and cause the development of fatigue are not entirely clear, it is believed that physical overload causes a gradual suppression of its activity, due to which the predominance of inhibitory processes begins. Probably the main role in this suppression is played by the above changes in the internal environment of the organism, in its organs and systems.
From all that has been said so far, it could be concluded that fatigue is definitely not a negative phenomenon, but an important signal to the body, aimed at preventing it from the occurrence of potential life-threatening phenomena. Therefore, when you do not have the strength to do anything, do not feel obliged to go to the gym, so as not to lose shape. On the contrary, listen to the signs of your body, eat well, take enough time to recover and sleep and rest. This will bring you even closer to the desired perfect shape and will guarantee you better health.
