Photoplethysmography

Stress is pervasive these days and so too is the use of wearable technology devices. Stress may appear to be reflected in your erratic training heart rates. While this may be the case, more than likely it’s your wrist-based heart rate monitor giving you strange readings. These monitors are fairly accurate in resting conditions, however once the activity really ramps up, along with the concurrent motion, their reliability may drop considerably without properly securing the monitor on your arm. Extra layers of clothes worn in the winter may add further motion artifacts. 

 Wrist-based heart rate monitors utilize photoplethysmography (PPG), which relies on the refraction of light from underlying blood flow, to determine heart rate. This technology has often been compared to more direct measurements of heart rate, that being from an electrocardiogram or chest strap. PPG, now ubiquitous in wearables, provides tremendous convenience and comfort for the athlete. In a recent study by Navalta et al. concurrent heart rate validity using various wearable technology devices was investigated (2020). The researchers concluded poor agreement between devices during an outdoor workout of variable intensity. Importantly, this typically reflects natural conditions for the athlete. 

 PPG technology is rapidly evolving and becoming more sophisticated with new product iterations. Research such as the aforementioned may cast doubt on the utility on this wearable device, however fastening your wrist monitor to a somewhat tighter setting and perhaps changing the location slightly may help ensure accuracy while you’re on the move, not to mention lower your stress level!