09/15/2026
PSA: if your heart rate while running is noticeably lower than it was a month ago, cooler weather could be the culprit.
Wrist-based heart rate monitors use an optical sensor, which typically emits green light. Blood absorbs this light, and when your heart beats, the volume of blood in the vessels under the sensor increases. The watch detects these changes in the amount of light reflected back to the sensor and uses them to calculate your heart rate.
But when cooler fall weather sets in, your body restricts blood flow to your extremities to conserve heat. That means there's less blood near the surface of your wrist for the sensor to detect, which can cause your watch to underestimate your heart rate.
And cold temperatures can also reduce battery performance, so your device may have a harder time keeping up in really cold weather.
The natural solution is to keep your wrist and watch covered. But assuming you actually want to, you know, read your watch, some tricks that work for me include:
🧣 Using a tubular scarf (eg. Buff) looped in a figure 8 on either side of my watch.
🧣 Wearing my watch on the underside of my wrist. That way, the fabric of my long sleeve naturally pulls away when I twist my wrist. This also seems to help keep the watch a little more protected from the wind.
🧣 In really cold weather, putting a very loose tubular scarf over my watch that I can easily pull away when I need to check it. Inconvenient? Yes. But a dead battery halfway through a winter run really stinks. 😂
Do you have any tricks for improving heart rate accuracy in cold weather? Drop them in the comments. I'd love to learn from you!