ALL ABOUT: Chest strap heart rate monitors

Tags: Technology and concepts | Smart

8.2.2022 | 6 MIN

Heart rate is the basis of every sport and, in fact, of our lives on earth. That is why it is important to have your heart under control, and chest straps are the most precise way to measure your heart rate.

Measuring heart rate using a chest strap is the oldest and, so far, the most accurate method of measuring heart rate and displaying values ​​in a watch or phone. The first chest strap with a coded signal for a watch was introduced in 1979. And the brand was Polar. Genuinely, in the begining, Polar had no real competition and ruled the sport tester market. But other brands like Timex or Sigma gradually joined in. All chest straps had a coded signal for one type of watch only.

The first chest strap in the world.

Measurement principle

The principle of measuring heart rate using a chest strap is based directly on the electrical activity of a heart. It is done by two diodes located on the chest strap, which sense the electrical activity. They are connected to a transmitter in the middle of the strap, which sends the data to smart devices (phone, watch) using Bluetooth signal or ANT+. We can see statements that chest straps measure with an accuracy of an EKG. New types of chest straps also have their storage for a certain number of hours, when they can store data directly inside them and then transfer it to the app on the phone.

Inside the sensor is a battery and a transmitter. The transmitter is connected to diodes on the side of the sensor, which record the electrical activity of the heart. The data is then shown on our smart devices.

Is the accuracy of the chest strap comparable to optics?

My colleague has already discussed how an optical heart rate sensor works in his article:

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The chest strap is more accurate because it directly measures the electrical activity of the heart, while optics measures the secondary occurrence – flowing blood. Since the optics takes measurements from a wrist, it is also affected by vibrations, shocks, and also cold, so it cannot be relied on in some conditions. If you tighten the sensor well on your body and moisten the diodes before use, it can be said that it should be almost 100% accurate.

Why and for whom is the chest strap suitable?

It is necessary to watch the proper activity level and have the right ratio of aerobic (slower) and anaerobic (faster) activities. Beginning athletes need to monitor their heart rate so they can see in which zone they are and thus move the performance further and form an aerobic base. This zone is also essential for beginners trying to lose weight by exercising.

The accuracy is important. Every athlete who wants to have their performance under 100% control should consider buying a chest strap. Especially if the person has any heart defect or arrhythmia. Failure to maintain the correct heart rate can lead to long-term overload of the heart, which can result in heart attacks and other diseases associated with this problem.

Chest strap test vs. optical sensor test

The test consisted of several parts, which included both running and various exercises, including quick lunges, burpees, and more. Looking at the graphs, it is obvious that the chest strap is more sensitive and more accurate than the optical heart rate sensor. The optical heart rate sensor (lower graph) slightly recorded the changes, while the chest strap offered an exact curve showing any small change in the heart rate.

The chest strap can also show other values

This is not the case for all types of chest straps, but some premium ones can also measure the heart rate variability (Suunto, Polar, mySASY, Garmin). But the heart rate variability is still a value associated with measuring heart rate. Garmin also added a feature measuring your running dynamics. It includes metrics such as ground contact time, the left/right foot balance, the vertical ratio, the vertical oscillation, stride length, and now also the running power.

These values are offered by Garmin premium chest straps HRM PRO, HRM RUN 2, and HRM TRI.

Running dynamics in training evaluation in Garmin Connect

What to look out for when using the chest strap

Not even the chest strap is 100% accurate if not used correctly. It is crucial to have it on correctly, tightened, and not forget about moistening the diodes. It should be tight enough. It should not constrict our breathing, but it should hold still and clasp the chest right under the breasts. The moistening of the diodes is then significant for conductivity. Dry diodes can distort data and measure inaccuracies. You can use tap water, but there are also special water-based solutions.

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Women generally have bigger problems with chest straps. It is necessary to choose the right underwear that will be compatible with the belt to avoid abrasions and sores. Some bras have a chest strap built directly into the hem, but this option is not yet common.

For men, a tight shirt might cause some problems as it can move the chest strap. When doing longer runs with running vests, there might be problems with the vest straps or the vest itself. For thinner individuals, the biggest problem may be to tighten the strap so that it does not fall and at the same time so that the individual can breathe.

Choosing the right chest strap is individual, depending on what you use the sensor for and also on the functions do you want from the sensor.

Comparison of sensors from different brand

Most of the brands also make heart rate sensors as accessories to watches. But it is not standard to use the same brand of sensor and watch. Since almost all sensors have one of the basic technology for transmitting signals (Bluetooth, ANT+), it is possible to choose whichever brand you want. For example, the Coros brand supports the connection of chest straps but so far has no chest strap in its offer.

Garmin HRM DUAL – Basic chest strap for heart rate measurementing. The sensor can be removed from the strap. This chest strap can be connected using Bluetooth or ANT+.

Garmin HRM RUN 2 –  A more advanced chest strap that measures heart rate and heart rate variability as well as running dynamics. The sensor can be removed from the strap.

HRM TRI – The strap is specially designed for triathlons, and therefore is adapted for swimming. When running, it also measures the running dynamics.

HRM PRO – The most expensive strap. The advantage is that it has storage for 17 hours of activity, where it is not needed to have a smart device connected to it. The sensor can be used for measuring heart rate during the date instead of an optical sensor.

Garmin HRM SWIM – This chest strap is designed for swimming only. It has a specially modified material, so it doesn't soak the water in and therefore isn't heavy on the body. This strap is also resistant to pool chemicals. If paired with a watch, it shows a heart rate on land like any other chest sensor. It doesn't show it underwater, but it records it to its storage, and you can later download it to your watch and see it after the activity is finished.

Polar H10 – Premium chest strap from Polar, with which you can swim thanks to 5 kHz data transmission (you can see the heartbeat directly in the activity). A big advantage of this strap are the silicone dots placed on the circumference, which hold the strap in its place during difficult training, and the atypical clasp. It also goes through chip updates taking place through the Polar Flow application. In addition to measuring heart rate, the strap can also record heart rate variability and has ANT + and Bluetooth technologies.

Suunto Smart Heart Rate Belt – The new chest strap from Suunto was released only recently, so it has not been possible for us to try it on. But according to the pictures and specifications, it can be said that Suunto continues with a great concept, having probably the smallest sensor of all straps on the market. In addition to measuring heart rate, the strap can also measure heart rate variability. Suunto equipped the sensor with Bluetooth technology only, not ANT +.