FAQ
Questions, answered.
Everything people ask about the Norwegian 4x4 protocol and the Viking 4x4 app. Deeper dives live in the science hub.
What is the Norwegian 4x4 protocol?
The Norwegian 4x4 is an interval workout: 4 minutes at 85-95% of your max heart rate, then 3 minutes easy, repeated 4 times, with a warm-up and cooldown. Developed at NTNU in Norway, it's one of the most studied methods for raising VO2 max.
Do I need an Apple Watch?
No watch, no problem: Viking 4x4 works as a fully guided timer. With an Apple Watch, the companion app launches automatically when you press start, streams live heart rate to your iPhone every second, mirrors your phase and countdown on your wrist, and saves the workout to Apple Health.
How is Viking 4x4 different from other 4x4 apps?
Most 4x4 apps time the protocol and show heart rate zones. Viking 4x4 measures whether it's working: after every interval it records how far your heart rate drops in 60 seconds (HRR-60), rates the session from Low to Elite, and trends your Recovery Score across sessions.
How often should I do the 4x4?
1-3 times per week. Once weekly was the dose used in the two-year study that improved VO2 max 18%. More isn't better for this protocol.
Is the Norwegian 4x4 safe for beginners?
It's demanding. Start with shorter work intervals and build up, and talk to your doctor before starting any high-intensity program, especially with existing heart conditions.
What heart rate should I hit during work intervals?
85-95% of your max heart rate, sustained for the full 4 minutes. The app shows a live target and tells you when you're in the zone.
Does Viking 4x4 sync with Apple Health?
Yes. Workouts save with your chosen activity type, heart rate samples, and calories. Your data stays on your device and in your Health app. No account required.
What's heart rate recovery and why does the app track it?
The drop in your heart rate 60 seconds after peak effort. It reflects cardiac efficiency, and in a major NEJM study, slower recovery predicted mortality. Watching it improve is the clearest sign the 4x4 is working.
How much does Viking 4x4 cost?
Free to download, and your first full 4x4 session is free. Unlimited workouts are $6.99/month or $29.99/year (about 64% less than monthly), cancel anytime. US prices as of October 2026; the App Store shows your local price.
How do I cancel my Viking 4x4 subscription?
Subscriptions are managed by Apple: open iOS Settings, tap your name, then Subscriptions, and choose Viking 4x4. Cancel at least 24 hours before renewal. Deleting the app does not cancel the subscription.
Why didn't the Viking 4x4 Watch app start?
Right after you install (or reinstall) the iPhone app, watchOS installs the companion Watch app on its own schedule, usually within a few minutes with your Watch nearby and unlocked. Until it finishes, the workout screen shows the Watch status and keeps tracking heart rate from Apple Health instead.
Can I do the 4x4 on a bike or rower instead of running?
Yes. Any cardio you can push to 85-95% max HR works. The app supports running, cycling, rowing, elliptical, stair stepper, and more.
SKÅL!
Your heart. Stronger. Provably.
Your first 4x4 is free · iPhone · Apple Watch companion