How to get the best heart rate reading from your watch (especially in winter)

All COROS watches are equipped with a wrist-based optical heart rate ( OHR ) sensor providing a convenient way to monitor Heart Rate without additional accessories. Therefore, athletes can determine their training zones, overall training load and necessary recovery.

Optical heart rate sensors are generally considered as an estimate of your effort. Athletes following HR based training programs are recommended to use heart rate straps and armbands ( which can be paired to COROS watches via ANT+connection ). Here is why:

In the technology world, all sensors including OHR will receive two things: signal and noise. Signal includes everything that’s helpful to your sensor reading, while noise is what keeps disturbing your sensor from providing correct measurements. If the sensitivity of a sensor is enhanced, it often increases both the signal and noise, causing an imperfect result. Most HR chest straps are equipped with technologies to receive less noise and stronger signal resulting in superior heart rate tracking performance than OHR during interval training.

Optical HR sensors rely on the reflection of the remaining green light after certain light got absorbed by the blood under your skin to determine the pulse frequency. COROS watches have four OHR algorithms built in: running, cycling, swimming and interval running. They are customized to different types of workouts to give you the best accuracy possible. Since heart rate sensors worn on your wrist are more prone to noise interference, the wearer should take the following steps to increase the signal and reduce noise as much as possible.

Here is what you can do to increase the signal:

  • Keep your hands warm.
    The OHR signal comes from your blood reflection. So, the more blood flow you have, the better signal your watch will receive. The weather doesn’t need to be freezing to impact your OHR accuracy. As long as your hands feel cold, your blood flow is reduced significantly. The best way to solve this is to wear gloves. Another suggestion is always warm up your body ( and your hands ) before starting your workout in the winter.
  • Clean skin without heavy hair or tattoos.
    It’s not a surprise that heavy hair and/or tattoos block the light refection and cause issues. If you have a tattoo ( s ) on one of your wrists, it is recommended that you switch your watch to the other one.
  • Wear the watch higher than your wrist bone.
    This is useful especially for those who have skinny wrists, as you need to find the areas of skin with more blood flow in order to properly use the OHR.
  • Wait for your watch to display a stable HR reading.
    Just like your body, your OHR sensor requires some warmup too. It’s recommended to stay on the “Start” page and wait a little longer so the watch can filter some noise by itself. Our watches also provide an alert beep to let you know when it’s ready to go ( if sounds are turned off, you will see a heart symbol which will be solid and steady when ready ).
  • Select the proper training mode.
    The regular running, cycling and swimming algorithms are not specifically built for tracking rapid changes in heart rate. When you train with intervals, please select the Interval Training mode under Run mode for enhanced heart rate tracking sensitivity.

Here is what you can do to reduce noise:

  • Wear it tight.
    The shake from running cadence is one of the key factors that cause a discrepancy. You want to wear your watch as tight as possible yet is still comfortable enough to limit the watch’s ability to move on your wrist. Athletes often find their watch OHR reading higher during aggressive downhill running because this is when you have the strongest steps.
  • Pick a lighter watch
    The heavier the watch is, the stronger the noise that will be created from your running stride. Generally, a lighter watch will maintain a stronger signal for a longer time.
  • Reset your OHR sensor in the middle of your run.
    Sweat/water will increase the chance of your watch moving on your wrist. So, it’s not a surprise if your OHR is working fine during the early stages of your run and becomes inaccurate later on. It could be that your hands got colder reducing blood flow, or your wrist had some sweat causing movement of the watch. Take your watch off, wipe your sweat and keep your wrist dry. Touch the OHR sensor to your running apparel instead of your skin so the reading goes away. Put it back on and resume your run. Most likely you will get a good reading again.
The bottom line is, if you are a data geek or going through heart rate training programs, it is definitely recommended to use chest straps or arm sensors for training. COROS watches are compatible with many 3rd party HR sensors with ANT+connection. Here are some external sensors that are commonly used by COROS wearers. Keep in mind using external sensors will increase the watch battery consumption.
  • Polar OH1
  • Polar H10
  • Garmin HRM Dual/Tri
  • Wahoo TICKR