N4x4 vs Four by Four (fa7b3d)

The best Norwegian 4x4 App on the App Store. Train the Norwegian 4x4 without watching the clock or guessing your effort. N4x4 reads your live heart rate — from Apple Watch, AirPods Pro 3, Garmin, WHOOP, Polar, or any Bluetooth monitor — and turns it into clear push, hold, and ease-off cues through every interval. When you finish, you see exactly how long you held the target zone, and how today compared with last time. Four 4-minute efforts, three easy recoveries. 33 minutes, warm-up and cooldown included. It trains VO2 max, the fitness marker most closely tied to how well you age, and it's one of the most studied ways to raise it. If you're going to invest time in your health, this is a strong place to start. HIT THE RIGHT ZONE • Target zones calculated from your own max heart rate • The number turns orange when you're below the zone and red when you're above, on both iPhone and Apple Watch • Spoken and haptic nudges when you drift out and stay out • A haptic countdown into every interval change: two taps, then the buzz USE THE SENSOR YOU ALREADY OWN • Apple Watch: install N4x4 on your wrist and heart rate streams automatically • AirPods Pro 3: the earbuds you're already wearing double as your heart rate monitor (iPhone on iOS 26) • Garmin (Broadcast Heart Rate), WHOOP (HR Broadcast), Polar, Wahoo, COROS, Powerbeats Pro 2, and any standard Bluetooth chest strap or armband • Wearing more than one? You choose which source wins • A built-in guide with exact, per-model setup steps EASY TO KEEP THE HABIT • Voice coaching through every interval, with the phone locked and your music ducked • Night-before, morning-of, and comeback reminders — each on its own switch • Weekly streaks, and a Live Activity on the Lock Screen and Dynamic Island FINISH WITH PROOF • Every interval charted against its target zone • Time in zone, time to zone, and a note per interval for your settings • Last session laid over today's, so progress is easy to see • Your usual workout — Cycle, Run, Kettlebells, and more — pre-selected when you save SEE THE PAYOFF • Your VO2 max trend from Apple Health • Training calendar, milestones, and full session history Works on the treadmill, rower, bike, stair climber, with kettlebells, or on the open road — any cardio that gets your heart into the zone. No account. No subscription. No ads. Your data stays on your device and in Apple Health. Start with one hard session a week. Add a second when you're ready.

Norwegian 4x4 interval training is the gold standard for improving VO2 max -- and Four by Four is the only app built specifically to coach you through every second of it, live from your Apple Watch. The protocol is simple: four rounds of 4-minute high-intensity intervals at 85-95% of your max heart rate, separated by 3-minute active recovery periods. Researchers at the Norwegian University of Science and Technology proved this method delivers dramatic cardiovascular gains in just weeks. Four by Four turns that science into a guided workout you can do anywhere. HOW IT WORKS Strap on your Apple Watch and tap Start. Four by Four reads your heart rate in real time and tells you exactly what to do. Speed up. Slow down. You are in the zone. Audio coaching cues play through your headphones so you never have to look at your wrist. The app walks you through a complete session: warm-up, four high-intensity intervals, three recovery periods, and a cool-down. Every phase is timed. Every transition is announced. All you have to do is run. REAL-TIME HEART RATE COACHING Your heart rate zone is front and center. A large, color-coded display shows whether you are below, inside, or above your target zone. Audio cues adapt in real time -- if you drift too low, the app pushes you. If you spike too high, it tells you to ease off. Zones are calculated from your age and resting heart rate using the Karvonen formula, the same method used in the original Norwegian research. APPLE WATCH INTEGRATION Four by Four runs a native watchOS companion app. Heart rate data streams directly from the watch sensor to the phone over WatchConnectivity. The workout is recorded as an official HealthKit workout, so it counts toward your Activity rings and appears in Apple Health. WHAT'S INCLUDED - Guided Norwegian 4x4 interval workouts - Real-time heart rate monitoring via Apple Watch - Audio coaching cues during every phase - Personalized heart rate zones based on your age - Warm-up and cool-down phases included - Workout summary with interval breakdown - Phase-by-phase timeline of your heart rate - Interval consistency tracking across sessions - HealthKit integration for workout recording - No account required -- just set your age and go BUILT FOR RUNNERS Whether you are training for a 5K or building your aerobic base, the Norwegian 4x4 protocol is one of the most time-efficient ways to improve your cardiovascular fitness. Three sessions a week, 35 minutes each. That is all it takes. Download Four by Four and start your first workout today.