# NTRVL: 4×4 Trainer — Norwegian 4×4 VO2Max Training

> Norwegian 4×4 VO2Max Training (iPhone/iPad app by Andrii Gryshutkin.)

- Source: https://appshunter.io/ios/app/ntrvl-44-trainer/id6768314931 (this page in markdown: same URL + `.md`)
- Developer: [Andrii Gryshutkin](https://appshunter.io/developer/1884593015)
- Category: Health & Fitness, Lifestyle
- Price: Free with in-app purchases
- Age rating: 4+
- Requires: iOS 17.0 · 3 MB
- Languages: American English
- Released: 2026-05-16
- Data updated: 2026-05-30
- User reviews in markdown: https://appshunter.io/ios/app/ntrvl-44-trainer/id6768314931/reviews.md

## What is NTRVL?

ADD YEARS TO YOUR LIFE IN 40 MINUTES A WEEK.

NTRVL is the cleanest way to do the Norwegian 4×4 — the interval protocol that 30+ years of research has shown to raise VO₂ Max faster than any other workout. And VO₂ Max isn't just a fitness number. It's the single strongest predictor of how long you live.

You don't need a gym. You don't need a trainer. You don't even need an Apple Watch. If you have AirPods Pro 3 or Powerbeats Pro 2, you already own a medical-grade heart-rate sensor — NTRVL just turns it into a coach.


THE PROTOCOL

• 10-minute warm-up
• 4 × 4 minutes in Zone 4 (90% max HR), with 3 minutes of active recovery between
• 5-minute cool-down

That's it. Forty minutes, twice a week. Backed by NTNU in Trondheim, where the protocol was developed.


WHAT NTRVL DOES

• Reads your live heart rate from AirPods, Powerbeats, or Apple Watch
• Calculates your personal training zones using Karvonen HRR + Tanaka max HR — auto-adjusted for your age, resting HR, and biological sex from Apple Health
• Adaptive warm-up — the next phase doesn't start until your heart is actually ready
• Real-time zone feedback so you know if you're working hard enough (and back off when you're not)
• Apple Watch companion — see your zone, BPM, and remaining time from your wrist
• Tracks every session in Apple Health as a real workout, with energy burned and HR samples


WHY VO₂ MAX MATTERS

Higher VO₂ Max is linked to lower risk of cardiovascular disease, dementia, type-2 diabetes, and all-cause mortality. A 5-point increase in VO₂ Max can add years of healthy life. The Norwegian 4×4 raises VO₂ Max more than any other protocol of equal duration. NTRVL gives you a structured way to do it for the rest of your life.


PRIVACY

Your heart-rate data never leaves your iPhone. No accounts, no servers, no analytics on your health. Everything is processed locally and stored in Apple Health, where you own it.


REQUIREMENTS

• iPhone running iOS 17 or later
• A heart-rate source: AirPods Pro 3, Powerbeats Pro 2, or Apple Watch (Series 4+)
• Optional Apple Watch companion app for wrist-based control


NTRVL Pro (free 7-day trial)

Unlock custom interval lengths, session history with PDF export, VO₂ Max trend charts, and training-load tracking.

ntrvl.app

—
Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
Privacy Policy: https://www.ntrvl.app/privacy

## Pricing and in-app purchases

Base price: Free.

**Subscriptions**

| Subscription | Price | Period |
| --- | --- | --- |
| NTRVL Pro Yearly | $29.99 | per year |
| NTRVL Pro Monthly | $4.99 | per month |



## Version history (last 1 release)

### 1.0 — 2026-05-16

No release notes.

## More apps by Andrii Gryshutkin

- [Heart Sit](https://appshunter.io/ios/app/heart-sit/id6760467612)
- [KettlePulse](https://appshunter.io/ios/app/kettlepulse/id6761713734)
- [Tactu: Pain Journal](https://appshunter.io/ios/app/tactu-pain-journal/id6762459710)

All apps by Andrii Gryshutkin: https://appshunter.io/developer/1884593015

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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 2026-05-30.*