# N4x4 — Gold Standard for VO2 Max

> HIIT trainer for VO2 Max improvement using the Norwegian 4x4 protocol. (iPhone/iPad app by Jan van Rensburg.)

- Source: https://appshunter.io/ios/app/n4x4/id6686407796 (this page in markdown: same URL + `.md`)
- Developer: [Jan van Rensburg](https://appshunter.io/developer/1688121173)
- Category: Health & Fitness
- Price: Free
- Rating: 4.30/5 from 10 App Store ratings · 5 written reviews indexed
- Age rating: 4+
- Requires: iOS 17.5 · 14 MB
- Languages: American English
- Released: 2024-09-16
- Data updated: 2026-08-12
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/n4x4/id6686407796/reviews.md

## What is N4x4?

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.

## Key features

- 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

## Recent user reviews (5 of 5)

All indexed reviews: https://appshunter.io/ios/app/n4x4/id6686407796/reviews.md

### 5/5 — Great and Free

*2026-07-14*

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

**Developer response:** 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.

### 5/5 — Excellent update

*2026-07-13*

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!

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

### 2/5 — No live Heart Rate

*2026-05-27*

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

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

### 3/5 — Needs HR in display

*2026-05-21*

All it shows is time and target heart rate in the interval.  Takes up whole screen as it should…but didn’t find a way to display my live heart rate.  So it’s just a timer if you ask me.

**Developer response:** Full Apple Watch integration in latest version. Enjoy :-)

### 5/5 — 10/10

*2024-10-11*

The app does exactly what it should and it does so with style.

## Frequently asked questions about N4x4

### 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.

## Version history (last 5 releases)

### 4.14 — 2026-08-04

The best Norwegian 4x4 app on the App store. Some fixes, thanks to Tal for the feedback.

### 4.13 — 2026-07-26

Cosmetic updates

### 4.12 — 2026-07-24

Cosmetic fixes.

### 4.10 — 2026-07-23

Small fixes.

### 4.8 — 2026-07-22

AirPods Pro 3 Heart Rate
• Wear AirPods Pro 3 and see your live heart rate during workouts — no watch
  or strap needed (iOS 26 required). Enable it under Settings → Heart Rate
  Sources.
• Using more than one sensor? Choose which wins: reorder Bluetooth monitor,
  Apple Watch, and AirPods in Settings.
• Powerbeats Pro 2 also work — pair them as a Bluetooth heart rate monitor.

Redesigned Settings
• Organised like the iOS Settings app: grouped, searchable, two taps to
  anything. Most-used settings sit at the top and show their current value.
• Reminders are now individually controllable: night-before, morning-of, and
  comeback nudges.

Choose Your Default Workout
• Pick the workout you actually do — Cycle, Run, Kettlebells, and more — and
  it's pre-selected every time you log a session.
• Kettlebells is now fully supported, with setup guidance and rep logging.

Better Interval Haptics
• A haptic countdown before every interval change: two short taps, then a
  long buzz as the new interval starts — on both iPhone and Apple Watch,
  whatever your audio setting.

Plus
• Training Tips lives on the Home screen.
• The post-workout summary shows the workout type right at the top.
• Fixed a bug where workouts were logged twice when using Apple Watch.

## Apps similar to N4x4

| App | Rating | Price | Category |
| --- | --- | --- | --- |
| [Tabata & HIIT Timer - PEAKVO2](https://appshunter.io/ios/app/tabata-and-hiit-timer-peakvo2/id6532617265) | — | Free | Health & Fitness |
| [Boost VO2 - Norwegian 4x4](https://appshunter.io/ios/app/boost-vo2-norwegian-4x4/id6748565289) | — | Free | Health & Fitness |
| [Norwegian 4x4 HIIT - Myworkout](https://appshunter.io/ios/app/norwegian-4x4-hiit-myworkout/id6497329690) | 4.7 (15) | Free | Health & Fitness |
| [VO2Max Training](https://appshunter.io/ios/app/vo2max-training/id6751254440) | 4.5 (8) | Free | Health & Fitness |
| [4x4 HIIT](https://appshunter.io/ios/app/4x4-hiit/id6755360081) | — | Free | Health & Fitness |
| [HIIT 4x4 Lite](https://appshunter.io/ios/app/hiit-4x4-lite/id1558498996) | 5.0 (2) | Free | Health & Fitness |

## More apps by Jan van Rensburg

- [SunUp Reminder](https://appshunter.io/ios/app/sunup-reminder/id6449208224)

All apps by Jan van Rensburg: https://appshunter.io/developer/1688121173

## Related topics

[norwegian 4x4](https://appshunter.io/ios/topics/norwegian-4x4) · [4x4 hiit](https://appshunter.io/ios/topics/4x4-hiit)

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-12.*