Heart Rate Zones: Underdog

Underdog turns your Apple Watch heart rate data into a game. Every minute you spend in Zone 2 — the sweet spot for endurance and fat burning — earns you points. Compete in weekly leagues with friends and climb from Bronze to Diamond. No manual logging. No ads. Just open the app once and your workouts sync automatically from Apple Health. WHY ZONE 2? Zone 2 training (60–70% of your max heart rate) is the foundation of every elite endurance program. It builds your aerobic base, improves VO2 max, and burns fat — without burning you out. The catch: most people train too hard to actually be in Zone 2. Underdog shows you exactly when you're in the zone. FEATURES * Automatic Apple Watch sync — workouts appear in seconds * 5 heart rate zones (Z1–Z5) calibrated to your max HR * Weekly leagues: Bronze, Silver, Gold, Platinum, Diamond * Points for every Zone 2+ minute * Achievements, streaks, and personal records * Friend leagues — invite via link * VO2 max tracking from Apple Health * Works with running, cycling, rowing, hiking, and 40+ workout types FREE Underdog is free to use. Optional Underdog Pro unlocks unlimited friend leagues, advanced stats, and custom zones. TERMS & PRIVACY Terms of Use (EULA): https://tryunderdog.com/terms Privacy Policy: https://tryunderdog.com/privacy Subscriptions auto-renew unless cancelled 24 hours before the end of the current period. Manage in Settings → Apple ID → Subscriptions.