How a Heart Rate Monitor Works

Using a Heart Rate Monitor

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A heart rate monitor (HRM) is a device you wear to measure and display your heart rate continuously. Electrode sensors in a chest strap detect each heartbeat and transmit the data to a receiver display such as a watch, fitness wearable, or phone app. The data is displayed as the number of beats per minute. Personal heart rate monitors are used to measure exercise intensity so you can know whether you are achieving the level of effort you targeting.

Heart rate monitors using chest straps with electrode sensors are considered to be as accurate as electrocardiograms (EKG). This sets them apart from arm- or wrist-based LED heart rate sensors such as are found in many fitness bands and smartwatches. While that technology is improving, it is less accurate.

Continuously Tracking Heart Rate

Heart rate monitors can continuously track and record heart rate during exercise, as compared to an on-demand pulse monitor which only shows a value at a single point. This frees you from having to stop and take your pulse to determine how intensely you are exercising.

Most heart rate monitor models have indicators showing whether you exercising in your chosen heart rate zone and give audible or visual alerts when you are above or below that zone. This allows you to adjust your workout to stay at your target heart rate by slowing down, speeding up, or changing incline or resistance.

Many heart rate monitors save and display the workout heart rate on a graph compared to time, speed, elevation and other aspects measured during the workout. The time in different heart rate zones may be shown at the end of the workout. Simpler heart rate monitors may only show the average heart rate for the session.

Heart Rate Monitor Design

Polar company founder Seppo Säynäjäkangas invented the wireless personal heart rate monitor in 1977 in Finland. His company was instrumental in popularizing it for athletes worldwide through the 1980s. As a result, these devices are often called Polar monitors, even though they are now produced by many manufacturers.

A wireless EKG-accurate heart rate monitor uses a strap around the chest that has electrode sensors that can detect the electrical activity of the heart as it beats. It then transmits this data to a receiver which processes and displays the signal as beats per minute.

The chest strap can be made of plastic, elastic, or fabric. The sensors can be embedded in it or attached. Sensors can also be embedded in the fabric of a sports bra or shirt rather than a strap. The original sensors needed to have moist contact with the skin to get accurate readings. To get a good contact, you might wet the contacts with saliva or a medical-grade gel such as used for ultrasound scans.

Originally, the signal was sent by radio waves to the receiver. Technology has developed to send it through ANT or Bluetooth. This enables devices such as cell phones and other mobile devices to use apps to receive data from the heart rate monitor sensors.

The receiver can be a watch display, wearable device, fitness band, mounted display for a bicycle, consoles on treadmills and other cardio machines, or mobile phone apps.

Heart Rate Zone Training With a Heart Rate Monitor

Walkers, runners, bikers use heart rate monitors to achieve the intensity of workout they want and to stay in their chosen heart rate zone. Various models have other functions such a stopwatch, GPS speed and distance, time of day, pre-set workouts, and calories burned.

Bluetooth heart rate monitors can transmit the data to your cell phone app where it can be used along with speed, distance, incline, and other workout data. For use without carrying a phone, various wrist or bicycle displays can also show a variety of information and sync with an app or workout website for detailed information after your workout.

In choosing a heart rate monitor, look for one that has the type of display you can most easily use and understand during your workout. Often they have pre-programmed exercise zones based on your age, while others allow you to set your zones to your individual preference.

Strap vs. Strapless LED Heart Rate Detection

Wearable devices can use LED lights on the wrist or arm to detect blood flow and count heart rate beats per minute. Fitness bands such as the Fitbit Charge and smartwatches such as the Apple Watch read heart rate continuously during workouts or can display your heart rate on demand at other points of the day. While this technology is improving in accuracy, many experts say it is still prone to inaccuracies. A study of the Fitbit Charge 2 found it consistently underestimated heart rate by 5.9 beats per minute, and the accuracy of Fitbit's LED heart rate detection is the subject of a class-action lawsuit. It can be wise to check your heart rate with an electrode strap heart rate monitor to see how a wrist-based LED device is performing for you.

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