The Relationship Between Heart Rate & Exercise Intensity

Trail runner looking at sport watch
A woman is checking her exercise monitor. (Image: blyjak/iStock/Getty Images)

A linear relationship exists between exercise intensity and heart rate. As exercise intensity increases, so does the heart rate. So one way to measure the intensity of your workout is to gauge how hard your heart is working. For example, a brisk walk around the track will increase your heart rate, but a jog around the track will really get your heart pumping.

Your Maximum Heart Rate

Your maximum heart rate (MHR) is the highest heart rate your cardiovascular system can effectively cope with during physical activity. A simple way to calculate your MHR is to subtract your age from 220. For example, a 30-year-old’s MHR would be 220 minus 30, or 190. So 190 is the maximum number of times a 30-year-old’s heart should beat each minute during exercise and physical activity. However, certain medications and physical factors can cause the MHR to be higher or lower.

Intensity Levels and Heart Rate

During low-intensity exercises, the heart beats well below its maximum rate. As exercise intensity increases, the heart rate moves closer to its maximum rate. Low-intensity exercises raise the heart rate to 40 to 50 percent of an individual’s MHR. Moderate-intensity exercises increase the heart rate to 50 to 70 percent of the MHR, while vigorous-intensity exercises elevate the heart rate to 70 to 80 percent of the MHR.

Target Heart Rate Zone

The target heart rate zone is the optimum level to exercise and reap the maximum cardiovascular and weight-loss benefits without overworking the heart. To determine your target heart rate, you need to know your MHR and the intensity level of your workout. For example, a 30-year-old planning to complete a moderate-intensity workout would have an MHR of 190 (220 minus 30) and the moderate workout’s intensity would be 50 to 70 percent of the maximum heart rate. To compute the target heart rate, multiply 190 by 0.5 to get the lower range of the zone then multiply 190 by 0.7 to get the high end of the target zone. So the 30-year-old’s target heart rate zone for a moderate-intensity workout is between 95 and 133 beats per minute.

Determining Your Heart Rate When Exercising

An easy way to determine your heart rate and the intensity of your workout while exercising is to stop, take your pulse for 15 seconds then multiply that number by four. For example, while exercising, the same 30-year-old stopped and took his pulse by placing his index and third fingers over the radial artery in his wrist and counted 31 beats in 15 seconds. He would multiply 31 by four to get his actual heart rate, which would be 124. This means his workout is in the moderate-intensity range for his targeted heart rate zone.

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