If you've ever been out for a steady tempo run and over time, you notice that your heart rate is increasing, even though you're maintaining the same speed, the same intensity of effort over a period of time. Well, that means you've actually experienced heart rate drift. I'm Jesse Funk and on today's episode of Runner's High, we're going to talk about what heart rate drift actually is and how it affects your performance.
If you just want a definition of what heart rate drift is, well, you got it in the intro. Heart rate drift is when your heart rate increases as you are working out and maintain the same intensity over time. Now, if you want to know what's physically going on, what's actually going on with our heart inside of us; let's talk a little bit more about the anatomy of your heart and what's happening as you're working out.
There's two main components with your heart that I want to talk about that relate to cardiac drift. And that is heart rate, which is often measured in beats per minute. We often talk about it, beats per minute, that's your heart rate, okay. And then also stroke volume, which is the total amount of blood being pumped out of your heart in one stroke, in one beat.
So, these two things work together in, you know, kind of concert to make sure that your muscles and whatever needs oxygen is getting enough oxygen; muscles specifically while you're working out. So, when you begin working out, beats per minute goes up and stroke volume goes up. They both increase for a while so that your total output is going up.
They both plateau and then we noticed over time that stroke volume, the amount of blood that your heart is pumping, out actually goes down. So, then beats per minute has to go up if you're maintaining the same intensity so that the total volume of blood remains the same, and your muscles can continue to get the same amount of oxygen over time.
One research study I saw suggested that this heart rate drift really starts to occur in at least moderate to high-intensity exercise, maintained over periods. So, that's why in the beginning, I said tempo work at around the 30-minute mark. That's when they start to see that decrease in stroke volume and then a consequent uptake in heart rate beats per minute because again, you want to maintain that total volume of blood going out. Now, that's the actual physical mechanics of what's happening with heart rate drift. And we don't necessarily know how to control all of it yet, but there is a component that we have control over and that is hydration.
In that research study I just mentioned, they're actually looking at cyclists, cyclists doing a test over two hours. What they noticed was that the cyclists that were allowed to replace their lost liquids had lower cardiac drift than those that were not allowed to replace liquids at all. It was actually twice as high in the athletes that were not allowed to replace their fluids compared to those that were. Now we're talking about a five and 10% drift, respectively. Meaning, if your workout rate say it was 100 beats per minute, it would drift it to 105 or 110, respectively.
Now, those are obviously nice numbers. I know when I'm doing a moderate intensity workout, I'm closer to 160 hundred, 170 beats per minute. But it was just nice, easy math for the camera here talking to you going off of 100. I actually got a suggestion from my friend Todd Buckingham when I interviewed him on the Smart Athlete Podcast. If you haven't seen that, hit that button wherever that is, subscribe to the channel, go check that out here in a second, Episode 29 to get all of Todd's tips.
But Todd suggested to me because I have problems in the heat, losing water, and then your muscles aren't gonna work as well, and you're not going to work as well. He mentioned that I can preload electrolytes the day before a race. And the consequence of this is that I stay more hydrated for the race, increasing that stroke volume we talked about earlier, making it larger, and lasts longer because of that extra hydration.
So, you can take multiple approaches to reducing this cardiac drift again, based on Todd's suggestion here. So, I'm kind of making a theory out of it that if you preload electrolytes before say a race, in particular, and then you also are replacing during that race, you should help reduce your cardiac drift. Meaning, your fatigue level should stay down, lower compared to if you're not doing those other things.
So, that's kind of the gist of cardiac drift. Do you have any comments, questions for me, anything you'd like to see in future videos? Leave them down in the comments below, let me know, I'd love to hear from you. I'll see you next time on the next episode Runner’s High.