What changes in blood plasma volume, hemoglobin levels and hematocrit might be expected to occur in the first few days following an exhaustive, long duration exercise bout?

Question

What changes in blood plasma volume, hemoglobin levels and hematocrit might be expected to occur in the first few days following an exhaustive, long duration exercise bout?

Answer 1

"The first few days" specifies a pretty short time-frame, which means that the body would not have had any chance to respond by changing composition of blood to any significant degree. In point of fact, we probably wouldn't see such a change anyway, unless your exercise program occurred in an area with a higher or lower oxygen level than your norm (as when athletes choose to exercise at high altitude where low oxygen will drive an increase in production of red blood cells (RBC's) in order to try to bring aerobic performance back to normal. Therefore, hemoglobin levels should not change significantly.

However, in the short term, particularly since your exercise is defined as "exhaustive," you may become dehydrated, and that WILL change some of the components of your blood. Since your plasma is mostly water, as you become dehydrated that water will be drawn out into other tissues by osmosis. So your plasma volume will decrease slightly. Since your hematocrit is the proportion of your blood's volume which is taken up by RBC's, the decrease in your plasma volume will tend to raise your hematocrit as your RBC's will take up the same amount of space but the overall blood volume is decreased.