I have been a personal trainer for over 20 years. And one of the most frequent questions that I get asked is about heart rate. If you've ever exercised before, then you know that your heart rate goes up when you work out, but do you know why? Why does heart rate increase during exercise?
The simple answer is that when you exercise your heart has to work harder to get the blood to your muscles. When you work out your muscles increase their activity. Because of the increased activity, your muscles need more oxygen. To meet that demand, your heart has to beat faster.
When your body is at rest, your heart doesn't have to work as hard. The majority of the heart's work when you're at rest goes to your vital organs. However, when you start exercising your heart has to pump out blood to your extremities. The more you move, the faster your heart will beat.
That's the simple answer, but there's a whole lot more to it. Let's take a closer look.
So Why Does Heart Rate Increase During Exercise?
Your muscles contract when you work out. In order to do that the muscle requires glucose, oxygen, amino acids, and a molecule known as ATP. The muscles contract as they use these compounds. But that's only part of the process.
As your muscles contract, they also produce waste products like lactic acid and carbon dioxide. If that waste remains on the muscle, you will end up with pain or discomfort. That's where your heart comes in.
Your heart does double duty when you exercise. It both brings the blood and nutrients to the muscles, and it carries away the waste. Your heart is continuously doing both of those things simultaneously. That's a lot of work!
So when you're wondering about, "Why does heart rate increase during exercise?" it's not hard to see how the heart would have to beat much faster to pull off that double duty, pushing blood throughout the whole body. The harder you work, the faster your heart will beat.
Your cardiac output increases along with your stroke volume because of the rise in blood flow to your muscles when you exercise. That increased cardiac output is in direct proportion with your oxygen consumption increase. You've probably noticed that when your heart rate goes up, you also start breathing faster.
How Do I Check My Heart Rate?
Now that we've reviewed why does heart rate increase during exercise, let's take a closer look at your heart rate.
The easiest way to find your heart rate is to use a heart rate monitor. There are many good ones on the market. Some have bands that go around your chest. Those are usually slightly more accurate. Others just use a watch. It's a good idea to wear it both while you exercise and when you want to find your resting heart rate.
If you don't have a heart rate monitor, you can find your heart rate by holding your finger lightly over your pulse and counting the beats for 10 seconds. Then multiply that number by six to get your beats per minute.
Your Maximum Heart Rate
While we're talking about why does heart rate increase during exercise, I'd like to point out a few more things about your heart rate.
First, we need to discuss your maximum heart rate. Bear with me for a minute here because we need to do a little math.
In order to find your maximum heart rate, you subtract your age from 220. So for example, if you're 40 years old, you subtract 40 from 220 to get a max heart rate of 180. That means that the fastest your heart should ever beat during exercise is 180 beats per minute.
Now that doesn't mean that you should try to get your heart rate up to 180 the whole time you're working out. It doesn't mean that at all. No, that's your maximum. You don't want to work at the max. Instead, you want to work in your target zone.
How do I find my target heart rate during exercise?
Now that you know how to find your max heart rate you can calculate your target heart rate zone. That's where you want to be working throughout your training. The target zone is generally between 60 and 85 percent of your max heart rate. If your goal is to burn body fat, then your target zone is between 60 and 70 percent of your maximum rate.
According to the American Heart Association, for moderate-intensity exercise, you should be working at 50 to 70 percent of your max heart rate. As I just said, this is where you will burn the most fat. For vigorous-intensity exercise, you will work at 70 to 85 percent of your max heart rate.
As you can see, there's a lot more to understanding your heart than just answering the question, "Why does heart rate increase during exercise?"
Here's how you calculate your target heart rate:
We already established that you get your max heart rate by subtracting your age from 220.
So for a 40-year-old, the maximum heart rate would be 180. From there you need to find your resting heart rate. You can find it by taking your pulse first thing in the morning when you wake up or when you are at rest. Once you know your resting heart rate, you can find your heart rate reserves. To calculate that you subtract your resting heart rate from your max heart rate.
For the sake of this example, let's say that our 40-year-old has a resting heart rate of 70. That means we are going to subtract 70 from 180, giving us a heart rate reserve of 110. If this 40-year-old wants to burn fat, he or she will want to work between 60 and 70 percent intensity. So we are going to take the heart rate reserve of 110 and multiply it by 0.6 (60 percent) to get 66. Then we will take 110 and multiply it by 0.7 (70 percent) to get 77. Next, we are going to add back in the resting heart rate of 70 to get 136 and 147. That's your target heart rate zone.
That means that throughout your workout you want to keep your heart rate between 136 and 147 optimally.
What should my resting heart rate be?
Since we're talking about why does heart rate increase during exercise, I need to mention a bit on resting heart rate. The resting heart rate for most adults is between 60 and 100 beats per minute. If your resting heart rate is above 100, you need to see your doctor.
Generally speaking, the lower your resting heart rate is, the healthier and more efficient your heart will be. For example, well-trained athletes often have resting heart rates between 40 and 50. On the other hand, a couch potato who never exercises will usually have a resting heart rate closer to 100.
The good news is, the more that you exercise, the lower your resting heart rate will become. One of my clients started a walking program last year. Over the course of the year, his resting heart rate went from 90 to 60. That's a significant improvement!
How Fast Your Heart Rate Should Come Down After Exercise
When you ask the question, "Why does heart rate increase during exercise," you also have to ask how quickly your heart rate should come back down afterward.
As a general rule, the faster your heart rate recovers back down to normal after exercise, the better shape you're in overall. That's why exercise stress tests measure your recovery time.
In the first minute after you stop exercising, your heart rate drops the most sharply. After that first minute, your heart will slow by around 20 beats per minute until you recover. Dropping at less than 12 beats per minute is considered abnormal.
Is it possible to lower your heart rate during exercise?
Yes, it is. As we discussed when we were talking about why does heart rate increase during exercise, your exertion is directly related to how high your heart rate goes. So if you find that you're having trouble staying within your target heart rate zone while you're working out, you just need to decrease your intensity. Slow down your jog. Make your movements smaller. To lower your heart rate over the long-term, you need to exercise more. The more fit you get, the slower your heart will have to beat.
How can I lower my resting heart rate?
As I mentioned earlier, lower resting heart rates indicate better heart health. Having a higher resting heart rate is not a good thing. But there are ways to lower your resting heart rate. First, you likely need to exercise more. Working out every day will gradually slow your resting heart rate.
Another thing you can do is to reduce stress. You should also avoid tobacco. Smokers have higher resting heart rates, but quitting will bring it back down. Finally, if you are overweight, losing a few pounds will also help to slow your resting heart rate.
The Bottom Line
The bottom line is that your heart rate is going to go up when you exercise. Your physical exertion requires more blood and oxygen than when you're at rest. One thing that's important to note is that with an increase in your cardiac output you are also increasing your cardiac stroke volume and your systemic vascular resistance. Those increases will also elevate your blood pressure. However, you can get a net decrease in your blood pressure when you're at rest in the long term by exercising.
Now we want to hear from you! Let us know in the comments section below if you have more questions about heart rate and exercise.