About this tool

Underdog turns heart rate zone training into a weekly competition. It reads heart rate and workout data from Apple Health — 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