There are four main components of blood: red blood cells which aid in the exchange of blood gases; white blood cells that fight against disease and infection; platelets which are primarily responsible for blood clotting ability; and plasma which is mostly made of water, hormones, proteins and minerals. The effects that prolonged exercise can have on plasma volume rests mainly on how water is distributed between intracellular fluid, which is found inside the body cells and extracellular fluid that surrounds the body cells, as well as the demands of the peripheral circulation versus the central circulation.
Electrolytes
Electrolytes such as potassium, magnesium and phosphate dominate the intracellular space, and sodium, calcium and chloride are found in the extracellular space. The electrolyte composition is much higher in the intravascular space and this difference pulls the plasma in to the blood vessels. The theory of drinking sports drinks containing electrolytes is supported by these facts.
Exercise
When a person is engaged in exercise, the muscles release protein into the plasma in the form of proteins such as albumin. Albumin also adds to the increase in plasma volume by attracting more fluid into the vascular system. In order to supply the major organs of the body with oxygen and nutrients during prolonged exercise, it is vital to maintain the intravascular plasma volume.
Hydration
In an article by Maughan, Bethell and Leiper in 1996, the discussion of the results of experiments regarding effects of fluid ingestion on exercise capacity and cardiovascular and metabolism responses to prolonged exercise in man, finds that initially plasma volume tends to decrease during prolonged exercise. It significantly decreases after the first 15 minutes, especially if you don't hydrate with fluid during exercise . It was also found that after the initial 15 minutes, the plasma volume gradually returns to pre-exercise level once hydrated.
Sodium
The American Heart Association reports that the enzyme renin plays a major part in regulating blood pressure which will increase markedly if a low amount of sodium is maintained. Brain natriuretic peptide also decreased significantly which concludes that plasma volume will decrease when maintaining a low-salt diet. When exercising, make a conscious effort to hydrate to keep the blood fluid and to keep the body hormones, oxygen and nutrients circulating and to keep plasma volume at a healthy level.
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