The fitness industry broadly uses the term 'Zone 2' to define a low-intensity cardio effort that allows for conversation but increases breathing. However, there is significant disagreement on the specific heart rate percentages that constitute this zone across various popular fitness platforms.
Heart rate zones are typically calculated as a percentage of an individual's maximum heart rate or heart rate reserve. For instance, Apple Watch defines Zone 2 as 60-70% of heart rate reserve using a calculated maximum and resting heart rate. Fitbit and Pixel devices use a 'moderate' zone (40-59% of heart rate reserve) with similar calculation methods. Garmin offers multiple definitions for Zone 2 depending on whether it's based on maximum heart rate (73-81%), heart rate reserve (65-75%), or lactate threshold heart rate (79-88%).
Other platforms also present variations. Orangetheory's 'blue' zone, analogous to Zone 2, is 61-70% of max heart rate. Peloton defines Zone 2 as 65-75% of max heart rate. The American College of Sports Medicine categorizes 'light' training (similar to Zone 2) at 57-63% of maximum heart rate, with 'moderate' at 64-76%.
Experts advise that rather than fixating on precise numbers, individuals should focus on the intended training effect and use perceived exertion as a guide. Aiming for an RPE of 3-4 on a 1-10 scale, where conversation is possible but breathing is elevated, can be more reliable. Over time, users can correlate their perceived exertion with the heart rate data displayed on their devices, trusting bodily signals over conflicting technological benchmarks.