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N4x4

N4x4

Gold Standard for VO2 Max

20 ratings
9 reviews
💪 Health & Fitness
Free

Details

Released
September 16, 2024
Updated
October 29, 2026

Features

Developer

Jan van Rensburg
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About

This app guides you through high-intensity interval training for VO2 max improvement. It uses your heart rate monitor to provide real-time cues and track your progress, making it easy to stay on track with your fitness goals.

✓Real-time heart rate zone guidance
✓Spoken and haptic interval cues
✓Supports various Bluetooth heart rate monitors
✓Workout progress tracking
✓VO2 max trend monitoring
✓Hands-free training support
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What's New in N4x4

5.14

October 29, 2026

More ways to record, share and personalize your Norwegian 4x4 workouts: • Apple Watch active calories can now be included in new Apple Health workouts when the required Health access is enabled. • Export saved workouts as FIT activity files for manual upload to Strava and other compatible services. • Give saved workouts your own names, with clearer activity-specific names and types for new Health exports. • Add one bonus round during your final work interval. Enable Show Bonus Round Button under Settings > Intervals & Durations; it stays hidden by default. • Choose and preview installed Apple English voices under Settings > Audio. Your current voice remains the default. • Improved startup: audio activates when you start a workout or preview a voice.

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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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Ccava3395

Response from developer

Thabk you for taking the time to review and report the issue. A new version (5.10) is awaiting Apple App Store approval. It includes some reliability improvements that I trust will resolve the issue. If not, please use the feedback option in the app and I will work with you to diagnose and fix it.

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!
PPulsar45

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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RRWaltonMouw

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.
CChuckDaniel1

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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Sseali33

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 N4x4?

N4x4 is a Health & Fitness app designed to guide users through the Norwegian 4x4 interval training protocol. It focuses on improving VO2 max by providing real-time heart rate zone feedback and interval cues.

How does N4x4 use heart rate data?

N4x4 connects to various Bluetooth heart rate monitors, including Apple Watch, AirPods Pro 3, Garmin, and WHOOP. It uses this live data to guide you into and out of target heart rate zones during your intervals.

What devices does N4x4 support?

N4x4 is available for iPhone and Apple Watch. It supports a wide range of Bluetooth heart rate monitors and can be used with treadmills, rowers, bikes, and other cardio equipment.

Is N4x4 free to use?

Yes, N4x4 is completely free to download and use. The app states there is no subscription, no ads, and your data stays on your device and in Apple Health.

Does N4x4 have ads?

No, N4x4 is ad-free. The app explicitly mentions 'No ads' in its description, ensuring an uninterrupted training experience.

How does N4x4 help track progress?

N4x4 charts each interval against its target zone, showing time in zone and time to zone. It also overlays your last session with today's to easily visualize progress and tracks your VO2 max trend via Apple Health.

What is the age rating for N4x4?

N4x4 has an age rating of 4+. This indicates it is suitable for users of all ages, with no mature content.

How often is N4x4 updated?

The latest version of N4x4 is 5.14, last updated on October 29, 2026. This suggests a history of regular updates and feature improvements.