Rapidly repeated or continuous contractions of muscle results in muscle fatigue.
Muscle fatigue is caused by a lack of oxygen in the muscle cells and build up of lactic acid.
Glucose > Lactic Acid + Energy
The process is not efficient and only a small quantity of energy is released and the cells can only work like this for a short time. So during intense exercise the concentration of lactic acid in the blood stream rises causing the discomfort and pain of muscle fatigue.
The advantage to the body is that more blood and therefore more glucose and oxygen is pumped to the muscle.
Trained athletes have a shorter recovery time than non-athletes. The heart of a trained athlete sends out…