It is known that a muscle cannot keep on contracting endlessly, for the duration of the contraction is limited by the appearance of fatigue.
The precise mechanism of tiredness is not completely made clear. Until not long ago the theories offered a unilateral explanation (lack of oxygen, exhaustion of energy resources, etc.), and they did not take into account the importance of the nervous system in the process of tiredness. Under the same name of “fatigue” we also list the physiological condition, which is different both in accordance with the causes which produce these states and with the effects on the body. These effects are of two kinds:
A muscle may be compared with a machinery which changes the chemical energy from the nourishing substances carried by the blood into mechanical energy. These products (glucose, fat, albumines, carbohydrates, etc.) appears as a result of digestion. In muscles they get ingled with the oxygen taken by the blood in the muscular fibres where they are oxidated at a temperature of 37º Celsius. This oxidation during the muscle activity is active and gives birth to resides.
The muscles get contracted only if they fulfil the following 2 conditions:
If one of these two conditions is not met, we get tiredness of muscular origin. It appears then the recovery of the muscle is not ensured or when the residues of the muscle fibres are not eliminated, resulting in the “poisoning” or intoxication of the fibre.
The cause of nervous fatigue is of another nature: strong emotions, losing beloved persons, longlasting conflicts, intellectual efforts, etc.
We shall give some indications in order to diminish nervous tiredness: