Surely many times have you wondered what this phenomenon is due. Normally, we use the term fatigue to describe general feelings of fatigue and accompanying reductions in muscle performance.

It is a defensive mechanism to adapt to the conditions, and aims to avoid possible adverse consequences arising from excessive practice.

Fatigue sensation originates in the hypothalamus and thalamus sensitive portion, and is expressed by modifying the normal functional behavior at different levels.

In most efforts, the causes of fatigue are focused on:

- energy systems. Phosphocreatine is used under anaerobic conditions to reconstruct the highly energetic as ATP to be used.

Glycogen may be a limiting factor, since muscles depend on a constant supply of glycogen to meet the high demands of own power exercise. Glycogen extend only allow contraction between 10 and 20 min., Especially if used in anaerobic conditions, low energy yield.

The use of reserves of muscle triglycerides impossible becomes anaerobically. Instead, under aerobic conditions, using AGL is favored, so there is a greater ability to mobilize fat reserves.

- Accumulation of metabolic waste. Lactic acid is a waste product of glycolysis, but only accumulates within muscle fibers during the realization of short and intense muscular effort. Fortunately, cells and body fluids have buffers such as bicarbonate, minimizing the disruptive influence of lactate and H +. Most researchers agree that a low muscle pH is the main factor limiting performance and the most important cause of fatigue during maximal exercise of short duration.

- Nervous system. Fatigue can occur in the endplate, preventing the transmission of the nerve impulse to the membrane of the muscle fibers; this may be due to a reduction of acetylcholine (neurotransmitter) or malfunction of cholinesterase.