N4x4

N4x4

Gold Standard for VO2 Max

15 ratings
7 reviews
Free

Details

  • Released
  • Updated
  • September 16, 2024
  • September 5, 2026

Features

N4x4 screenshot #1 for iPhone
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About

This app guides you through the scientifically-backed Norwegian 4x4 HIIT protocol to efficiently boost your VO2 Max and cardiovascular health. It offers set-and-forget workouts with visual and audio cues, suitable for all fitness levels.

Norwegian 4x4 HIIT protocol
Set-and-forget workout structure
Visual and audio interval cues
Real-time heart rate zone display
5-minute warm-up
4 rounds of 4-minute intervals
3-minute recovery periods
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What's New in N4x4

5.0

September 5, 2026

Standalone Apple Watch App. You don't need your phone to use N4x4 during workouts.

User reviews

Great App

Very nice app that is easy to use with ability to adjust elements of the training protocol to fit the need/capacity of people at different levels.
It would be good to be able to see my target HR range easier. Love the color coding, just need the numbers bigger when on my phone.
Love it! Exceptionally useful.
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VO2 max history chart missing

App works well for HIIT on my elliptical using a Garmin HRM chest strap, but the VO2 max history chart does not appear anywhere. Sharing with Apple Health is turned on, so I don’t know what the problem is.

Response from developer

The latest version of the app contains some troubleshooting steps. Please let me know if that doesn't solve your problem!

Great and Free

Exactly what I was looking for. Great UI, simple and focused on running for better health and better VO2max.
Suggestions:
1. Please add a feedback option in the app as a way to send feedback or bugs.
2. Would be highly appreciated if you could add support for health wearables that broadcast their HR (Like Whoop).
Thank you
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Response from developer

Thank you for the great feedback and review. I'm glad you alerted me that Whoop and other HR monitors could send real time heart rate. I mistakenly thought it was only Apple Watch. Whoop and Garmin integration is now in the new version.

Excellent update

I have been using this app for 6 weeks. The original version was basic and effective. For a free app, I couldn’t be happier. The update adds everything I was missing and compensating for by running multiple apps at the same time during the workout. Thank you!

Response from developer

Thank you so much for the time you took to leave a review. I'm glad you find it useful.

No live Heart Rate

Disappointing. Screen should show live heart rate or at least zone during the exercise.

Response from developer

Full Apple Watch (and more heart rate monitors) integration plus live HR display and real time voice coaching in the latest version. Enjoy :-)

Developer apps

FAQ

What is the Norwegian 4x4 HIIT protocol used in N4x4?

The Norwegian 4x4 HIIT protocol involves 4 rounds of 4-minute high-intensity intervals, with 3-minute recovery periods between each round. This structured approach is scientifically proven to be highly effective for boosting VO2 Max.

How does N4x4 help with VO2 Max?

N4x4 focuses on the Norwegian 4x4 HIIT protocol, which is recognized as one of the most efficient methods for improving VO2 Max. A higher VO2 Max is a key indicator of cardiovascular health and longevity.

Is N4x4 suitable for beginners?

Yes, N4x4 is designed for both beginners and advanced athletes. The app provides clear visual and audio cues to guide users through each interval, making it accessible regardless of fitness level.

Does N4x4 require a subscription?

No, N4x4 is completely free to use. The app states it has no strings attached, meaning there are no sign-ups, ads, or in-app purchases required to access its full functionality.

Does N4x4 have ads?

No, N4x4 is ad-free. The app explicitly states that it contains no advertisements, ensuring an uninterrupted workout experience for users.

What devices does N4x4 support?

Based on the provided data, N4x4 currently supports iPhones. Information on Android compatibility is not specified in the current data.

How often is N4x4 updated?

The latest version of N4x4 is 3.44, which was last updated on April 3, 2026. This indicates a recent update, suggesting ongoing development and support for the application.

What is the age rating for N4x4?

N4x4 has an age rating of 4+. This means it is considered suitable for users of all ages, with no specific content restrictions.