# Z2/4×4 Trainer — Zone 2 & 4×4 cardio coach

> Zone 2 & 4×4 cardio coach (iPhone/iPad app by Chenfei Chu.)

- Source: https://appshunter.io/ios/app/z244-trainer/id6776864990 (this page in markdown: same URL + `.md`)
- Developer: [Chenfei Chu](https://appshunter.io/developer/6776864992)
- Category: Health & Fitness, Sports
- Price: Free with in-app purchases
- Age rating: 4+
- Requires: iOS 18.0 · 5 MB
- Languages: American English, French (France), German (Germany), Japanese, Korean, Brazilian Portuguese, European Spanish, Chinese (Traditional, Taiwan)
- Released: 2026-07-07
- Data updated: 2026-10-11

## What is Z2/4×4 Trainer?

Z2/4×4 Trainer turns the two most effective endurance methods — easy Zone 2 base work and high-intensity Norwegian 4×4 intervals — into a simple daily plan built around YOUR heart rate.

WHAT YOU GET
• Daily and weekly Zone 2 prescriptions at 60–70% of your max heart rate to build your aerobic base.
• Norwegian 4×4 sessions: four 4-minute intervals at 85–95% of max heart rate, with 3-minute recoveries — the protocol used to boost VO2 max.
• Weekly health-maintenance and weight-loss targets to keep you consistent.
• Personalized zones from your max heart rate (220 − age), which you can override if you know your true max.

WORKS WITH APPLE HEALTH
• Pull in your heart rate, resting heart rate, active energy, body weight, and past workouts — or enter everything manually. Your choice.
• Completed Zone 2 and 4×4 workouts are saved back to Apple Health so all your training lives in one place.

IPHONE + APPLE WATCH
• Plan and review on iPhone; train with your zones on your wrist.

PRIVATE BY DESIGN
• 100% on-device. No account, no sign-up, no server.
• Nothing you enter or that we read from Apple Health ever leaves your device.
• No ads, no analytics, no tracking, no third-party SDKs.
• Your Health data is never used for advertising — ever.

WHO IT'S FOR
• Runners, cyclists, rowers, and anyone doing cardio who wants structure instead of guesswork.
• Beginners building a base and experienced athletes adding VO2-max work.

FREE + AN OPTIONAL ONE-TIME UPGRADE
• Everything above is free: guided workouts on iPhone and Apple Watch, plans, zones, Apple Health sync.
• One optional one-time purchase (Pro) unlocks the deeper coaching analysis: full readiness breakdown, overtraining guard, adaptive weekly progression, VO2-max trend, and CSV/JSON export. No subscription.

Z2/4×4 Trainer is a fitness and training tool, not a medical device. It does not diagnose, treat, or prevent any disease. Talk to a healthcare professional before starting a new exercise program.

## Pricing and in-app purchases

Base price: Free.

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| Z2/4×4 Pro (Lifetime) | $14.99 | one-time |


## Is Z2/4×4 Trainer safe?

Not enough ratings yet to assess Z2/4×4 Trainer.

## Is Z2/4×4 Trainer legit?

Z2/4×4 Trainer has limited verification signals. The AppsHunter Legitimacy Score for Z2/4×4 Trainer is 58 out of 100 points across 7 verification signals from App Store and developer data.


## Version history (last 3 releases)

### 1.0.2 — 2026-07-26

New in 1.0.2:

• Training guide — a new section under Settings explaining why Zone 2 and the Norwegian 4×4 work, and what this app does differently.
• Your call on hard days — when low readiness reduces a 4×4 to three intervals, you can now choose to run the full session anyway, on both iPhone and Apple Watch.
• More accurate history — a reduced 4×4 now logs its real duration instead of the full session's, so your weekly minutes and streaks reflect what you actually did.
• Redeem an App Store code for Pro from the upgrade screen.

Questions or feedback? Email ozzyfly@logolo.ca.

### 1.0.1 — 2026-07-09

• Optional one-time Pro unlock: full readiness breakdown, overtraining guard, adaptive coaching, VO2 max trend, and CSV/JSON export. Everything you already use stays free.
• 4 new languages — Korean, German, French, Portuguese (Brazil) — 8 in total, plus an in-app language switcher.
• Redesigned Apple Watch summary screens and Zone 2 live view.
• Overtraining protection: low-readiness guard on the watch and training-load warnings.
• Fixes: accurate interval timing with the wrist down, workout energy now saves reliably, localization polish.

### 1.0 — 2026-06-10

No release notes.

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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 2026-10-11.*