Have you ever paid close attention to your heart rate on a run? Especially if it was on a long run or race, you probably noticed that your heart rate gradually increased even if you were maintaining pace.
Why is this and what should we do about it?
This is called cardiac drift. It’s a natural phenomenon in endurance sports. It’s nothing to worry about but, if you train by heart rate or if you check on your heart rate after your runs, it’s something to be aware of.
What is cardiac drift?
Our heart rate naturally increases as we run. Why?
Dehydration is a large factor in cardiac drift. As your body gets more dehydrated, your blood plasma is reduced and your blood becomes thicker, harder to move through the vessels. This leads to your heart having to work harder to move the same amount of red blood cells.
Unless the dehydration is severe, this isn’t something to worry about. Just realize that even being slightly dehydrated can cause your heart rate to go up slightly.
Body temperature also plays a role in cardiac drift. As you get warmer, your body prioritizes maintaining a safe temperature above all else. One of the most effective ways to cool your body is to pump more blood to your skin, which is why your skin might look more pink or red after a hard workout in high temperatures. If more blood is going to your skin, your heart will have to work harder in order to provide the same amount of blood to your working muscles.
Hormones/stress/fatigue also play a role. This is a pretty small role but fatigue stresses the body, which causes hormones to be released that affect your heart rate.
What should we do about cardiac drift?
Accept the drift. Don’t fight it.
If we’re training by heart rate and don’t account for cardiac drift, we’re going to slow throughout a run to maintain a given heart rate target. Experienced runners and coaches know we ideally want the opposite. Maintain a steady pace or even get slightly faster as the run goes on. This means don’t panic when you see your heart rate gradually increasing throughout a run. Instead, just keep doing your thing and let your body do what it needs to do.
If you want to train by heart rate, target ranges, not precise numbers. Start at the lower end of the target range and understand that, as the run goes on, you’ll naturally move toward the higher end of the range.
Especially on race day, don’t worry about the drift. Consider the factors I mentioned above. You might experience a bit (or a lot) more of each of those things when you’re pushing yourself to the limit on race day. If you’re feeling as good as should be expected and running well, don’t slow down on race day just because your late race heart rate may be higher than expected from earlier in the run.
Hi! I´m googling cardiac drift and high heart rate during easy runs and saw I could comment here so why not ask.
I´m a runner, 40 female, in pretty good shape, although stressed out and probably a bit to much caffine and sugar at times, running in pretty cold weather usually. Heart is fine, resting heart rate around 50.
I see that many people seem to have high heart beat during easy runs, so do I. Question is, I feel okay, should I worry about my heart workload, as I am running around 100 km pr month year after year… is it more unhealthy than healthy making my heart beat so fast?
Example: I went out with my 10 year old this morning, super easy (6 min/km), just talking and jogging for 30 minutes, still heart beat average 160, max 180 after the cardiac drift where it just stays up in the 170 something. Last week I hiked pretty fast up a mountain (950 m up) for 45 minutes, I am really pushing hard walking uphill but my heart beat stays around 100… Then the easy fun part starts, jogging downhill and what happens, my heart beat instantly goes up to 160 and then up to 180 (my garmin watch, it´s the same with a strap). I have tried buteyko breathing, cooling down, slowing down… but still my cardiac drift is most often high and reglular easy run is averace 160, max 185 regularly.
Does someone have the answer to if this causes to much strain on the heart?
Kindest regards from Iceland!
Hello Laufey,
I’m not sure if what you’re experiencing fits the technical definition of cardiac drift. However, assuming you have no medical concerns (and I definitely would encourage you to ask your doctor as I’m neither a medical professional nor there to examine you in person) I wouldn’t be too concerned about your heart rate as long as you are still breathing in a controlled manner and, as it sounds like, able to talk while running. The old standard for easy running is the “talk test”. If you can hold a conversation, you’re keeping your easy run adequately easy.
I do have a couple of things on my mind:
1) Have you done a max heart rate test? I wonder if your max heart rate is quite high and that’s why you hit those high numbers. Maybe you are at a lower percentage of your max than you realize.
2) It’s hard, though not impossible especially if we do have underlying conditions, to put too much strain on the heart. The old idea that your heart has only so many beats before it can’t keep up has no basis in fact to back it up. Besides, I long ago did a little thought experiment to prove how off that idea is. If the average resting heart rate is 70 beats per minute and a fit person’s resting heart rate is 50, as you say yours is, you’re “saving” 20 beats per minutes for about 23 hours a day, 1200 beats per hour or over 27,000 beats in 23 hours. Even at 170 beats per minute average for the other hour, your heart would beat just over 10,000 times in that hour or 6000 “excess” beats over the average person’s resting rate. You’re “saving” over 21,000 beats per day in this scenario.
All of this said, again, this all assumes you are running at that conversational pace and that you’ve assured with your doctor that you have no underlying conditions.