How reliable are smartwatches for measuring heart rate?

05 Tem 02:38

Smartwatches primarily use two types of sensor technology for heart rate monitoring: green light (PPG - Photoplethysmography) and red/IR light (transmissive-type sensors). PPG sensors work by measuring light absorption in blood flow under the skin, estimating pulse. During exercise, sensitivity can drop by 5-15% due to muscle movement and skin perfusion issues. Sensors using red/IR light (common in medical devices) provide more accurate results but are rarely used in smartwatches due to design complexity and reduced battery life. PPG performance degrades significantly in stressful situations or high-intensity activities (e.g., treadmill speeds above 12 km/h). Some premium smartwatches (like Apple Watch Series 8+, Garmin Forerunner/Vertix) approved by the U.S. FDA attempt to minimize errors using advanced algorithms and multiple PPG sensors, but they still aren’t as precise as clinical ECGs. If medical-grade accuracy is needed, devices capable of 30-second ECG readings (e.g., Apple Watch) are currently the best short-term alternative.

05 Tem 03:15

While green light sensors (PPG - Photoplethysmography) are the most common technology used in smartwatches for heart rate monitoring, the system is far from simple. The basic principle involves detecting changes in blood volume in the capillaries near the skin. However, the biggest issue here is that the sensor can only read the surface of the skin. During exercise or stress, blood flow intensifies, which can lead to inaccurate readings. For example, if there's a direct vein in your arm or if your movement disrupts the sensor's contact with the skin, you'll see significant fluctuations in the data. Accuracy rates vary by brand. A study on Apple Watch's PPG system (Chen et al., 2019) showed an average accuracy of around 95% for heart rates between 100-140 bpm. However, this rate can drop to 80% for heart rates above 140 bpm or during high-intensity activities. Models like Garmin with ECG support (e.g., Venu 2 series) can provide more stable results since they can also measure the heart's electrical activity. Still, the main limitation of PPG is its dependence on "light intensity." If your skin is dark, your blood pressure is high, or your movement is too vigorous, the sensor may struggle to read the data accurately. If high precision is required, measuring closer to the actual source of the heart rate is essential. Earbud-type sensors (e.g., Polar H10) or chest straps are much more reliable than PPG because they detect heartbeats directly. For wrist-worn sensors, try to keep your arm steady, ensure full contact between the sensor and skin, and wear the device snugly (but not too tight). The type of activity also affects sensor performance; for instance, PPG may provide healthier results during controlled activities like cycling, but accuracy can significantly drop during running or weightlifting.