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Plasma volume expanasion (Hypervolemia) generally accres with acute endurance activity and endurance training both in human beings and animals.
In more cases, the expansion in plasma volume is associated with lower
hematocrit without red cell mass alteration or an actual reduction in red cell
mass, causing relative to true anemia, respectively. Both exercise and heat acclimatization (which also produce hypervolemia, but in a lower degree than
exercise) Increase hypervolemia induced by exercise training alone. The onset of the pheromone is so rapid that hypervolemia could be observed at minutes
of hours as of the time of the of cessation of the exercise. After a marathon or a longer distant run, the plasma volume expansion needs a couple of days to
reach its maximum level. The magnitude of this natural expansion ranges from 9% to 25%, corresponding to an extra 300 to 700 ml of plasma. The
magnitude of this alteration before training depends on ambient conditions, intensity of exercise, duration of activity, body posture and frequency of the
exercise bouts. The larger the reduction in hypervolemia during exercise, the larger the subsequent hypervolemia. The hydration conditions of the subjects in pre and post exercise could also modify plasma volume alterations (enough fluid ingestion can lead to hypervolemia even during prolong training).
Fluid regulating hormones includig aldosterone, arginin vasopressin
and atrial natriuretic factor, In relation to an elevation in plasma protein content increase hypervolemia. However, the key role and the mechanism of
the increase in protein content remain unclear and hormonal role in the induction of chronic hypervolemia is still a question that has to be answered.
Plasma volume expansion could promote performance by induction of


better muscle perfusion, and by enhancing stroke volume and peak cardiac output. By enhancing skin blood flow, hypervolemia also enhance
thermoregulatory responses to exercise that is the key role and important concept of optimal plasma volume and hematocrit and performance.