Smartwatch accuracy: What affects heart rates?

Smartwatches have become popular tools for tracking fitness and health, but their accuracy can vary depending on several factors. Skin tone, tattoos, age-related changes, and exercise intensity can all impact the precision of wrist-based heart rate sensors. Studies have shown that melanin, the pigment responsible for skin color, can absorb light at specific wavelengths, complicating readings in individuals with darker skin tones.

Tattoos can also interfere with readings, as the ink pattern and color saturation can block the sensor’s light. While age-related skin changes were initially thought to affect accuracy, research has shown that heart rate readings are generally accurate irrespective of age. However, exercise intensity can play a significant role in accuracy.

A study examining wrist-based sensors from brands like Apple, Fitbit, TomTom, and Samsung against the gold-standard ECG found that at higher exercise intensities, Fitbit and Samsung tended to underestimate heart rate values, while TomTom and Apple were more reliable.

Factors affecting smartwatch heart rate accuracy

Garmin and other manufacturers recommend using a chest-strap monitor for the best accuracy, particularly during high-intensity exercise.

Chest straps measure the electrical activity of the heart more directly, similar to an ECG. The importance of accuracy depends on how you use the data. For casual users interested in general trends, minor inaccuracies may not matter.

However, for serious athletes aiming to optimize every training session, accurate heart rate monitoring is crucial. Heart rate data can guide training intensity to optimize fat burning or carbohydrate usage, improve stamina, and enhance overall performance. While smartwatches offer convenience and useful data, their accuracy can be compromised under certain conditions, and serious athletes may benefit from using a chest-strap monitor to ensure they are training at the correct intensity.