Author: Prof. Dranda. Danielli Braga de Mello
Muscular fatigue is related to the sensation of tiredness, reduction in muscular performance and the decline in the capacity to generate maximum strength. Any imperfection in these neuromuscular components of muscular contraction can cause fatigue:
- The motor nerves that activate the muscular fibers by transmitting the nerve impulses.
- The neuromuscular junctions in transmiting the nerve impulses of the motor nervse for muscular fibers (more common in the motor units of rapid contraction muscular fibers - type II).
- The proper contractile mechanism in generating strength due to depletion of the reserves of ATP, phosphate and creatina, depletion of the reserves of muscular glycogen, lack of local oxygenation and the accumulation of lactate.
Lactate is the main metabolite responsible for the onset of the local muscular fatigue and it is produced by the glycolic anaerobic system, a result of the absence of oxygen.
The carbohydrates are transformed into our organism into simple sugar (GLUCOSE), and that blood sugar can then be used immediately to generate energy (by glucolise), or it is stored in the muscle as muscular glycogen and in the liver as hepatic glycogen through the process of glucogenese.
During glucolise molecules of ATP and piruvic acid are produced by the absence of oxygen, and transformed into lactate, which when accumulated in excess, along with other variables results local muscular fatigue.
This system has duration of approximately 1 ½ minutes, being characterized by activities of high intensity that demand force and speed.
The blood lactate concentration during the exercise is related to the intensity of the exercise, but it also is influenced by the duration of this exercise. However, the presence of this metabolite does not have to be understood as the great cause of the fatigue, and yes as a new source of energy supply since blood lactate through the oxidation and removal of the muscle, is transformed in the liver into glucose.
The capacity of oxidation and removal of the blood lactate is related to the level and specificity of the training, but it can be optimized with a good active recovery (through continuous exercises with low of intensity).