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Heart Rate Monitors: How They Work

Heart rate monitor watch
A man running with a heart rate monitor watch. (Image credit: <a href="">Maridav</a>, <a href="">Shutterstock</a>)

Heart rate monitors provide immediate feedback on how hard you are working out so that you can make adjustments to get the greatest benefit from your exercise regimen. The best fitness trackers often have some kind of heart rate monitor built into their design and while they're not always 100% accurate, they can give you some good health insights. 

According to the Centers for Disease Control and Prevention, for moderate-intensity physical activity a person's target heart rate should be 50 percent to 70 percent of his or her maximum heart rate. For example, using the results calculated above for a 50-year-old person, 50 percent and 70 percent levels would be:

  • 50 percent level: 170 x 0.50 = 85 beats per minute (bpm)
  • 70 percent level: 170 x 0.70 = 119 bpm

For intense exercise, a 50-year-old person's target heart rate should be 70 percent to 85 percent of his or her maximum heart rate:

  • 70 percent level: 170 x 0.70 = 119 bpm 
  • 85 percent level: 170 x 0.85 = 144 bpm

All exercisers can benefit from monitoring their heart rate during activity, enabling them to maintain fat-burning and aerobic target zones based on their goals.

Types of heart rate monitors

Heart rate monitors generally come in two types — either a wireless chest strap that sends data to a monitor worn on the wrist, or pulse monitor worn on the wrist that requires you to put your finger on a certain spot to take your pulse.

Both provide real-time input on how hard and how efficiently you are exercising. Heart rate monitors are typically used for cardiovascular exercise, such as walking, running, hiking, climbing and skiing.

The sports-watch models that connect to a chest strap allow for continuous tracking of your heart rate by sending the information to a monitor worn on the wrist. Some advanced models are synchronized with foot pods, which are monitors that are attached to your shoe, typically through the shoelace. This helps to track how far you have gone and how fast you have run to provide a more complete picture of your workout. This also provides the ability to compare performance over time. Some also are connected to GPS to allow for mapping of courses, saving favorite routes and comparing performance.

Higher-end models also have special coding to cut down on interference with other devices, which can happen in a gym setting or a race where a lot of people are wearing heart monitors.

There are also heart rate monitor watches that can be worn on the wrist but are not connected to a chest strap. These require that you touch your finger to a pad to get a pulse rate. This type of monitor requires that you stop exercising to take your pulse and tends to be less accurate than the chest-strap models.

Basic personal heart rate monitors generally display the time of your workout and give you continuous, average, high and low heart rate data and typically provide up to three target heart rates.

More advanced sports watches and fitness trackers provide up to six target zones and can also include features such as stopwatches, calorie counters, and speed and distance monitors, lap counters, recovery heart rate and time spent in the target zone.

Some gym equipment — such as treadmills, elliptical machines, stationary bikes and stair climbers — is also equipped with finger-based or chest-strap type pulse monitors.

There are times when your heart rate needs to be monitored in a medical setting. During an electrocardiogram (ECG or EKG) leads (electrical sensing devices) on the body in standardized locations, to provide information about cardiovascular health. During a stress EKG — also called an exercise EKG or a treadmill test — your heart  is tested to see how it responds to exertion.

Kim Ann Zimmermann
Kim Ann Zimmermann is a contributor to Live Science. She holds a bachelor’s degree in communications from Glassboro State College.