Underdog turns heart rate zone training into a weekly competition. It reads heart rate and workout data from Apple Health, whether that is an Apple Watch, a chest strap, or any connected sensor, and scores every minute you spend in zones one through five. There is no manual logging at any point. Zone 2 builds aerobic base and scores steadily, Zone 3 and above score higher, and running, cycling, strength work and HIIT all count on the same footing.
Those points feed weekly leagues that run from Bronze through Silver, Gold and Platinum to Diamond, with promotion and relegation each week; private leagues can be created and shared with an invite code.
Because scoring is based on heart rate as a percentage of your own maximum rather than pace or distance, a seventy-year-old and a twenty-five-year-old can post the same score: no pace bias, no gear advantage and no ability cliff. Each week you also get a zone breakdown, step trends and an intensity timeline showing when and how hard you pushed. The app is free with no ads, and health data stays on the device rather than being sold or used for advertising.
