Changes

This approach has been used for decades, and I had an early version back in the 1980s. The latest optical heart rate monitors are vastly superior, but still have many accuracy issues. The most accurate form of heart rate monitoring is to use a chest strap that picks up the electrical signal from the heart. While a chest strap is not perfect, it works remarkably well as long as it has good contact with your skin, the battery is not flat, and it's not malfunctioning. The accuracy of Optical Heart Rate Monitoring (OHRM) will depend on a number of factors:* The watch needs to fit just right. Because of the sensor is measuring the expansion of the capillaries with each heartbeat, too much pressure will prevent this expansion. However, to lose and the watch won't get a good reading due to lack of contact. Getting this tension just right can be tricky, especially if you're wrist expands or contracts over time.* Movement seems to confuse OHRM systems, possibly because it changes the papillary filling. Some users have noted that their OHRM systems seem to lock on to their Cadence rather than their heart rate.* Temperature seems to be a huge factor, and most systems work better in warmer conditions. If you're a little chilled, your body will restrict blood flow to your capillaries to retain body heat, making it much harder for the optical HRM. Of course, because the system needs to be against the skin, it can be tricky to use them in cold conditions. I've cut a hole in a arm warmer so that I can see the watch face while preventing frostbite to the surrounding skin.* It's possible that bright sunlight might also influence the accuracy, though I've not noticed any obvious correlation.