Can you please provide a definition for the term cardiovascular drift?
Cardiac drift, the most common term used for this occurrence, is defined as the rise in heart rate during exercise that occurs as a result of loss of blood volume principally from dehydration.
Here is an example of cardiac drift. You are training at a steady heart rate number of 76 percent of your maximum heart rate or within five beats of 156 bpm. You notice your speed or pace doesn’t change, but your heart rate after about an hour starts to rise as you maintain the same velocity. If you do not drink fluids, this gradual drift continues until you stop exercising. Physiologically what happens is that as you train at higher intensities, you produce heat, and in an attempt to cool your core temperature, your body sweats and draws water from the blood stream, decreasing blood volume. Since cardiac output (CO) must stay constant because of the energy demands, then heart rate (HR) or stroke volume (SV) must shift to accommodate this. Stroke volume is the quantity of blood that is pumped with each heart beat. The formula for this is quite simple: CO = HR x SV
Cardiac drift then is the slow increase in heart rate as a result of the need for the body to maintain a constant cardiac output and the inability to increase stroke volume due to the decrease in blood volume during exercise.
Thanks for the great question. I hope the answer was of equal value.