The Reason for Heart Rate Drift

Had an athlete inquire on heart rate increases throughout a workout. I figured I would share.....

Ever wonder why your heart rate increase as your exercise duration increases? For example, your heart rate will be higher at the end of your long run compared to when you started. That's simply known as cardiac drift. This is a standard physiological response to exercise over prolonged periods. What happens is your stroke volume (amount of blood the heart pumps with every beat) decreases with prolonged exercise. The large working muscles still require blood to perform exercise, so to get the needed oxygenated blood, the heart must pump a little more. This is why the heart rate will increase, without a change in intensity or perceived effort.