WHOOP utilizes a method called Photoplethysmography, or PPG, to track your heart rate 24/7. PPG monitors Heart Rate by shining light through the top layer of your skin. Various things, such as skin, muscle, fat, and blood reflects some of the light back into the WHOOP Strap’s sensor. The major varying component of this signal is the changing volume of blood under the sensor caused by your heart pumping blood. WHOOP monitors this signal and turns this recording of the changing amount of reflected light received by the sensor into a heart rate.
This technique works very well to monitor heart rate, however several sources of "noise" can corrupt the signal and affect the accuracy of the results. WHOOP has developed many proprietary techniques, hardware enhancements, and algorithms to reduce the impact of these noise sources and amplify the fundamental signal we are measuring.
Here are some best practices to make sure your Heart Rate is being captured as accurately as possible:
- Make sure the sensor is snug against the skin even during the most intense workouts. It is important for the WHOOP to be tight against the skin to minimize or eliminate relative movements of the sensor against the skin. It is important that the sensor is snug enough that it is always in contact with the skin. Learn how to adjust your band here.
- Some people may have anatomical features or participate in activities that cause large amounts of noise to enter the measurements. In these cases, if you notice a decrease in heart rate accuracy, often moving the strap up or down the wrist by 1 centimeter can result in much more accurate measurements.
- If it is more comfortable or allows for optimal range of motion in your workout, move the WHOOP Strap up toward the forearm or even on the bicep. Check out our accessories to allow WHOOP to be worn on the bicep here: https://shop.whoop.com/collections/gear
- Make sure the sensor is kept clean. Some WHOOP athletes do this by cleaning their WHOOP Strap with warm, soapy water while they shower.