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N4x4

N4x4

Gold Standard for VO2 Max

17 ratings
9 reviews
💪 Health & Fitness
Free

Details

  • Released
  • Updated
  • September 16, 2024
  • September 30, 2026

Features

Developer

Jan van Rensburg
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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

5.7

September 30, 2026

Recorded heart rate in Apple Health Your recorded heart-rate readings now accompany newly exported workouts, including readings from Polar and other Bluetooth monitors. Allow N4x4 to write Heart Rate in Settings > Health & Devices > Review Health Access. Improved Apple Watch reliability More reliable workout startup, heart-rate delivery and recovery after interruptions, with clearer connection status and a retry option on the Watch. Stale readings now clear from the display. Thank you for your feedback and support!

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User reviews

Most RecentHighest RatedLowest Rated

Glitch

There appears to be a glitch for me where it will not read HR data at all if I toggle Heart rate permission to be allowed. The app just will refuse to read the hr from my Apple Watch. If I leave Enable Apple Health off then it works and reads the HR from my watch. Could this please be looked at and fixed if possible. Thank you so much I absolutely love this app!
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cava3395cava3395

Excellent app

This is a great app for 4x4 workout. Coaches you and reads heart rate from watch in realtime. Developer improves app with each update. Thanks!
Pulsar45Pulsar45

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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RWaltonMouwRWaltonMouw

Response from developer

I appreciate the review and kind words, thank you. Let me know if this latest update is better. :-)

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.
ChuckDaniel1ChuckDaniel1

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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seali33seali33

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.

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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.