Exercise is any physical exertion of the body. It come in the form of physical activity, training or even daily activities. When the body undergoes exercises, various muscles are called upon to perform their assigned tasks. These muscles require more energy than when they are at rest. Energy is provided by cell respiration though glycolysis. C6H12O6 + 6O2 > 6CO2 + 6H2O + Energy released (2830 kJ mol? 1).
The increased consumption of oxygen disturbs the balance between oxygen and carbon dioxide levels within the body. Due to the excess carbon dioxide, the body is forced to obtain more oxygen in order to again attain homeostasis or balance. To obtain oxygen, the body performs more rapid breathing or panting. Sweat is also a result of exercise. Sweat is a fluid composed mainly of water with some salt and urea.
Sweating is primarily used to cool the body since the production of energy also produces heat. When sweat evaporates, heat goes along with it, thus achieving a cooling effect. Sweat also removes the water byproduct of cell respiration. With the removal of water, the balance between salt and water levels in the body is again destroyed. To restore it, thirst is felt to induce the person to search for water.
Reference: MARIEB. , E. N. (2006) Essentials of Human Anatomy and Physiology.