Best Heart Rate Monitor for swimming

Nowadays, some smartwatches allow you to record your heart rate while swimming. But not many models can do it and not always very accurately. In fact, the best way to record your heart rate while swimming is to use a dedicated HRM strap.

But which heart rate monitor (HRM) is best for swimming?

Comparison of heart rate monitor technology for swimming

There are 2 types of heart rate monitor technologies available on the market: using an optical sensor or using electrodes. Optical sensors are commonly found on watches and optical straps, and electrodes are used on chest straps. Let’s focus on these technologies with regard to swimming:

Optical HRM

They use the refraction of light to measure the change of blood pressure in your vessels. When light is emitted onto the skin, some of this light is absorbed by the blood vessels, while the rest is reflected back. The amount of light reflected back depends on the blood volume in the vessels. By monitoring these changes, the device derives your heart rate.

Challenges of optical sensors when swimming:

1. Water between the sensor and skin: If water gets trapped between the sensor and the skin, it can displace the light, causing either a diminished or erratic signal. It is also possible that the movement of the water can lead to false readings. Refraction can be a problem too.
2. External Light Interference: Underwater, especially in clear water with sunlight, external light can interfere with the light emitted by the sensor, potentially causing inaccurate readings.
3. Skin Changes: Water, especially for prolonged periods, can change the skin’s texture and properties. This could alter the way light is reflected and absorbed, potentially affecting the accuracy of the heart rate measurement.

Electrodes HRM (known as ‘chest straps’)

They use electrodes to detect electrical signals produced by the heart. It’s similar to the electrocardiogram (ECG) used in hospitals to measure the heart rate data.

Challenges of chest straps when swimming:

1. Consistent contact with the skin: For a chest strap HRM to work effectively, the electrodes need to maintain consistent contact with the skin. Movements, especially when pushing off the wall at the swimming pool, might cause the strap to shift, leading to intermittent readings or loss of signal.
2. Corrosion: The combination of moisture and salt (if swimming in the ocean) can lead to corrosion of the electrodes over time, which can reduce the lifespan of the device or cause it to malfunction. It’s easy to prevent if you wash your strap regularly.
3. Signal Transmission: If the chest strap HRM wirelessly transmits data (e.g., to a wristwatch or a swim tracker), there’s another challenge. Bluetooth signal, which is commonly used for wireless transmission, don’t propagate well in water. In short, chest straps do not broadcast live the heart rate data while underwater, but most can give you a summary of your heart rate each time you take a rest and then provide the full information once the swim is over.

Note: Chest straps can have some issues working well on some people and here are the solutions if that’s your case.

In summary, optical sensors are more prone to inaccuracies underwater than chest straps.

How to choose the ideal heart rate monitor for swimming

Here are the key features to look out for when buying a heart rate monitor for swimming:

• Waterproof rating

I guess this one is obvious. But not all heart rate monitors can go underwater. To swim with an HRM, it is recommended to have a rating of 5 ATM and avoid everything under 3 ATM.

Be cautious with straps with an IPX-7 rating. This certification ensures the device tested is waterproof at 1 meter for a period of 30 minutes. It might not be enough for swimming in a pool. Keep in mind that having no issues for a couple of swims with an IPX-7 or IPX-8 may not mean it will be okay for months.

Of course, a product can behave better than what it is certified for. The Wahoo Tickr for instance is used by many people for pool swimming despite being IPX-7. But you have to see it as the exception to the rule. I would really aim for straps rated as 5 ATM or WR50.

If a waterproof rating is given with a value of pressure, you can directly calculate how deep the HRM can go in the water. The waterproof rating definition is detailed on Garmin’s website.

For instance, Polar H10 chest strap rating is ‘WR30’. It means that it can withstand water pressure of 3 ATM (or 3 bar) without a limitation of time. This is the same as saying it can handle up to 30 meters underwater.

In summary:

• Usage

Whether you intend to use the heart rate monitor to swim at the pool or in open water is important when choosing an HRM.

At the swimming pool: chlorine will damage your HRM, especially the plastics of the watch and/or fabric of the strap. But also when pushing off the wall, you will notice that the chest strap can struggle to stay in place unless it is specially designed for it. So pool swimming will affect the most your HRM lifespan and efficiency. This is why you should look out for a device designed for pool swimming like Garmin HRM Swim if that’s your use case.

In open water: no issue unless you swim in the sea. Then, the salt can affect the fabric of the strap but not much compared to chlorine. And if you clean it after each use it will last through time.

Additionally, if you need to use the HRM for other activities than swimming, you might want to select one that matches your need: maybe you will want to have some additional running metrics, etc.

• Access to heart rate while swimming?

As mentioned earlier in this article, Bluetooth does not work underwater and therefore the information collected by the heart rate monitor cannot be transferred live to a device: unless you are recording directly with a watch. So chest straps cannot send data live to your watch. But in reality, you cannot swim and look at your watch at the same time, so having the information of your heart rate live is not useful.

What’s good is that many chest straps will provide you with some information (like live heart rate, min. and max. HR of the last interval) each time you take a rest, as long as you wear a compatible device (like a watch).

So here are some questions you should be asking yourself to select the correct strap for your needs:

• Accuracy

Optical sensors are less accurate than electrode sensors underwater in general. That’s why not many watches have the ability to record your heart rate when swimming. For accuracy, a chest strap is generally the best option.

How to wear a heart rate monitor when swimming

Whatever the heart rate monitor type you use, it must be tightly attached to your skin to prevent the water from finding space between the sensor and your skin.

Here I would like to focus for a minute on chest straps:

To prevent the strap from slipping it is recommended to wear your HRM strap under your bathing suit, trisuit, or a wetsuit. The idea is that the fabric will help maintain the strap tight against your skin. This is easy to do for women and also when swimming in open water.

But at the swimming pool, men generally do not wear a swimsuit that covers their torso. If you intend to swim regularly with a chest strap at the swimming pool, then I recommend you buy the Garmin HRM Swim which has a wider strap than other brands and models, specially designed to stay in place without wearing something on top.

Best heart rate monitors for swimming