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Heart Rate Training: Should I Use a Chest Strap or Watch?

Since our watches started telling us our heart rate data I have had a lot of clients ask if they need their heart rate straps anymore. 

And it seems like every week there are new devices that go on your chest or wrist, even on your earlobes or forehead to measure your heart rate! 

They all have pros and cons.

Understanding exactly how they work will help you make the best choice for your training goals. 

There are two main technologies that are used for tracking your heart rate. The first type monitors electrical signals from your heart, which is what a chest strap does. And the second option uses an optical system, which is what most wrist, earlobe or forehead-based systems use. 

Chest Strap Heart Rate Monitor

A chest strap heart rate monitor is my favorite way to do heart rate based training. 

In fact, chest monitors, when compared to ECG readings, are 99.6% accurate. At that accuracy rating, you know you are getting the correct heart rate at any given intensity. 


To use this tech accurately, it needs to be up against your skin just below your sternum. It needs to be snug enough so that the contact points stay in contact with your chest, but it can't be on so tight that it restricts your breathing. 

Sometimes when I'm using my chest strap heart rate monitor for really long runs and I'm moving all over, like when I'm doing a mountain run where I'm also using my upper body at some points, the monitor will get too loose or fall off. If that happens, you're clearly not going to get an accurate reading. So just make sure you snug it right up. 

If you are small, it can be tough to get a reading from the chest strap monitor at times.

If either situation has happened to you, gently wet the sensors on both sides of your monitor before you put it on. The moisture will help the chest strap stick to your skin so you can get an accurate reading.

Now, most people will just use tap water or snow if they have access to it. I have licked my heart rate monitor before…that can be a bit of a salty surprise if you haven't washed it after the last time you used it! 


The other thing to know about chest strap monitors is they need to be paired with a watch or an app on your phone in order to work properly. 

A lot of heart rate straps will be made specifically for a watch, and if you already have both of those units, you're ready to go. The devices may come together or they'll come with instructions on how to pair if purchased separately.

If you bought a monitor and you want to use it with your phone, there's just a couple of things you have to be aware of. You need to make sure that heart rate monitor you buy communicates in a language or send a transmission that your device understands. 

Most heart monitors will communicate in two types of communication: Bluetooth Low Energy (BLE) or ANT+. Just be sure that the monitor communicates in a way that the phone can pick up and you are good to go!

The final thing to remember is that Polar is the gold standard in heart rate strap accuracy. But because this technology has been around for a very long time, most heart monitors are going to be very accurate regardless.

Optical Heart Rate Monitors

The other method that is used to capture your heart rate is called an optical heart rate monitor. 

Optical heart rate monitors are in a lot of products on the market today. Most of them are measuring on your wrist. Some other monitors, like Move's latest heart rate monitor, measure through your forehead. However, wrist monitors are the product that people most often ask me questions about. 


On these devices, there are green LED lights and a sensor on the part that is in contact with your skin.

The way that optical heart rate monitors work is by analyzing the light that is refracted off of the blood that is running through your wrist. 

You probably remember from science class that hemoglobin is the molecule in your blood that holds oxygen and transports it to wherever it needs to go. With every beat of your heart, there is a pulse of blood that travels through the arteries underneath this monitor. Hemoglobin absorbs the green light that is being produced by the optical heart rate monitor. And by comparing low and high amounts of absorption the watch is able to detect when a pulse of blood has gone by the sensor. 

When the watch detects that pulse of blood, it marks that a heartbeat has happened. 


When compared to the chest based monitor, there's a lot more opportunities for interference with this method. 

These are the most common things that negatively impact an accurate reading with optical heart rate monitoring devices: 

  • For wrist monitors, arm movement during exercise can be falsely marked as a heartbeat.

  • Having generally high blood volume, such as when you're working at a very high intensity. 

  • Any dirt, salt or dead skin buildup on the actual monitoring unit will interfere with readings.

  • Optical monitors have a longer period of time between each measure, so they update your heart rate less frequently than chest strap monitors.

This monitoring method could actually be 10% off, which could be a bit of a problem.

Imagine if you're trying to keep your heart rate at 150 beats per minute. A 10% inaccuracy could make you think that your heart rate is only 135 beats per minute when it's actually 150. That's massive if you're using the heart rate zone system to train for a specific event! 


So what do you do? 

We need to make sure we're using tools that are accurate so that our training is productive. 

If you have a watch or other optical heart rate monitor, it doesn't mean you shouldn't use it. In fact, there is a lot of value in using an optical heart rate monitor. 

For high intensity interval training, I would strongly recommend using the chest strap. 

If you only have a watch and want to do higher intensity training, what I would suggest instead is use either an RPE scale (rate of perceived exertion) or how hard this feels out of 10. 

An optical monitor performs best in lower intensity training, like Long Zone 2 runs, recovery runs or tracking your heart rate all day. It is particularly helpful in tracking your resting heart rate, an important indicator for if you are over or under training. 

The cool thing about heart rate based training is we are able to listen to our body and we're also able to ignore pace, which can change greatly depending on the terrain you're on and the situation you're in. 

With heart rate based training, you're going to make progress and changes to yourself at a physiological level no matter the external stimulus that you're dealing with. 

And every once in a while, I encourage you to throw the heart monitors aside and take a run just for you. 

In fact, fitness is all about being able and capable of interacting with the world around you. So make sure you forget the heart rate monitor at home every once in a while! 


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