A Look Behind The Data: How WHOOP Measures Heart Rate

The heart rate algorithm is the backbone of many features (and other algorithms) on WHOOP, from calculating Daily Strain and Recovery Scores, to Sleep Cycles and more. Discover how it works and the recent updates and innovations that are improving accuracy.

What is Heart Rate?

Heart rate, often measured in beats per minute (BPM), reflects how fast your heart is beating in any given moment. Throughout the day, your heart rate changes in response to different physical and mental stressors. Your resting heart rate, and change in heart rate in response to exercise, are key indicators of cardiovascular health. Monitoring heart rate has long been a common practice for athletes to optimize their training, but it is also a critical indicator of overall health and fitness for everyone. 

How WHOOP Measures Heart Rate

WHOOP measures heart rate using advanced optical sensors with photoplethysmography (PPG) technology. It works by emitting green LED light into the skin, and then measuring the light that’s reflected back. Every time your heart beats, the blood flow increases, and this causes the amount of light that’s reflected back to change. WHOOP takes this raw data from the sensors and interprets it through an algorithm to produce a heart rate reading.

While raw data is captured using the sensor hardware, an algorithm is required to estimate heart rate. The WHOOP heart rate algorithm is a complex set of mathematical formulas and computational processes used to interpret the raw data collected by the sensors. The algorithm filters out factors like movement artifacts that occur when you’re in motion to accurately determine your heart rate. It also adjusts for factors like skin tone, age, and activity type, to ensure accurate measurements across different conditions and members.

WHOOP recently released an update to the heart rate algorithm that improves accuracy. The update is a culmination of thousands of lines of code and millions of data points. This update is another step in a continuous journey towards a best-in-class WHOOP experience. Improvements to the heart rate algorithm drive enhanced accuracy across the entire WHOOP experience, knowing heart rate informs many key metrics and recommendations.

Development and Testing of Heart Rate Algorithms

The development and testing of the heart rate algorithm involve rigorous processes to ensure accuracy and reliability. Over several months, our Signal Processing and Data Science teams collected primary data through our 24/7 research facility, WHOOP Labs. This data underwent extensive analysis and iteration to refine the algorithm.

Testing includes various stages:

1. Data Collection: Gathering data from a diverse group of users in a controlled and validated setting to create a primary data set, across factors like gender, age, skin color, and activity type.
2. Algorithm Development: Iterating on the algorithm to improve how it separates signal from noise and accurately measures heart rate.
3. Validation: Testing the algorithm across large population sets and in context of various related metrics on WHOOP to ensure its accuracy and reliability.

Our fully integrated approach—combining hardware, software, apparel, and WHOOP Labs in one location—enables seamless collaboration and rapid iteration, ensuring that every improvement is well-coordinated and effectively implemented.

Continuous Improvements

WHOOP is  designed  to accommodate new and regular updates without requiring the purchase of a new device. Updates are made through software or app improvements to ensure that the WHOOP membership continues to get better. Members are encouraged to ensure their app version is up to date to ensure they are experiencing the absolute best that WHOOP has to offer. Unlocking human performance drives our obsession with innovation and progress.