# HIIT 4x4 — Interval Training Meter

> Apple Watch HIIT interval training meter based on heart rate percentage. (iPhone/iPad app by Eastridge Technology.)

- Source: https://appshunter.io/ios/app/hiit-4x4/id1450845415 (this page in markdown: same URL + `.md`)
- Developer: [Eastridge Technology](https://appshunter.io/developer/392920417)
- Category: Health & Fitness, Sports
- Price: $9.99
- Rating: 1.00/5 from 1 App Store ratings · 4 written reviews indexed
- Age rating: 12+
- Requires: iOS 15.0 · 2 MB
- Languages: English
- Released: 2019-02-21
- Data updated: 2026-07-05
- Monetization: paid
- User reviews in markdown: https://appshunter.io/ios/app/hiit-4x4/id1450845415/reviews.md

## What is HIIT 4x4?

HIIT 4x4 is an Apple Watch exercise monitoring app for High Intensity Interval Training (HIIT). The app sequences exercise between high and low intensity intervals. The intensity of the exercise is measured as a percentage of a person's Maximum Heart Rate (MHR). 

The HIIT 4x4 intervals are as follows:

- 10 minutes warmup at 60% MHR
- 4 minutes high intensity at 90% MHR
- 3 minutes low intensity at 70% MHR
- repeat high-low intervals 4 times (4 high intensity intervals of 4 minutes each = 4x4).

HIIT 4x4 uses a speedometer type dial to display heart rate. When the arrow is in the green zone then your heart rate is within the interval target.  If the heart rate later  falls out of the target range, warning chimes are issued until back in range.

Each person's MHR is different, and changes with age. A commonly used formula for MHR is 220 - age in years. A more accurate number can be discovered by using a heart monitor during all out exercise and observing the highest heart rate achieved.

HIIT 4x4 stores your workout history using Apple Health. 

HIIT 4x4 is based on the High Intensity Interval Training 4x4 program developed by the Norwegian University of Science and Technology's Cardiac Exercise Group.

## Key features

- Heart rate zone monitoring
- Speedometer-style dial
- Warning chimes for out-of-zone heart rate
- Workout history storage via Apple Health
- Customizable MHR calculation
- Structured 4x4 HIIT program

## Recent user reviews (4 of 4)

All indexed reviews: https://appshunter.io/ios/app/hiit-4x4/id1450845415/reviews.md

### 1/5 — Worked until today

*2024-10-09, version 1.08*

This was a great app for a Norwegian 4x4. Its simplicity was a strength. However, with the latest WatchOS, it will no longer start up via the watch touchscreen on my v8 cellular watch. Bummer. 

My 3 stars is the average of a 5 and a 0, sort of. Hoping this gets fixed.

After a delay, here’s an update. The app did start working again after a week or so. My initial POV of good simplicity fell away when I realised that it was merely reporting HR data, but not any GPS, pace, cadence, stride, etc. 

I tried using the Apple workout app simultaneously, but HIIT would lock up. Because this app used the same audio alert for starting/stopping an interval and being in the target HR or getting too high or low, I completely missed starting an interval. When I cancelled this app, and just used the built in Timer app, I discovered that my Workout app had been stopped as well. 

I just deleted this completely. Waste of time.

### 3/5 — Worked until today

*2024-09-17*

This was a great app for a Norwegian 4x4. Its simplicity was a strength. However, with the latest WatchOS, it will no longer start up via the watch touchscreen on my v8 cellular watch. Bummer. 

My 3 stars is the average of a 5 and a 0, sort of. Hoping this gets fixed.

### 1/5 — No info on Charges

*2021-12-03, version 1.04*

Never really used the app. I can’t find a place where I can cancel the charges on this app if I decide I don’t want to keep using it. I paid $1.99 but it’s not clear if it renews automatically or is it just a one time charge.?. Doesn’t show on subscriptions on iPhone. Frustrating.

### 1/5 — Not worth the money

*2019-11-24, version 1.03*

I spend too much time looking at my watch to see where my heart rate is at. It distracts from the actual work out. This was a waste of 2 bucks. Avoid!

## Frequently asked questions about HIIT 4x4

### What is the workout structure for HIIT 4x4?

HIIT 4x4 follows a structured 4x4 program. It includes a 10-minute warmup at 60% MHR, followed by 4 minutes of high intensity at 90% MHR and 3 minutes of low intensity at 70% MHR. This high-low interval cycle is repeated four times.

### How does HIIT 4x4 measure exercise intensity?

Intensity is measured as a percentage of your Maximum Heart Rate (MHR). The app uses a speedometer-style dial to show if your heart rate is within the target zone for each interval.

### Does HIIT 4x4 store workout data?

Yes, HIIT 4x4 stores your workout history by integrating with Apple Health. This allows you to track your progress over time.

### What devices is HIIT 4x4 compatible with?

HIIT 4x4 is designed for Apple Watch and is also supported on iPhone and iPod devices.

### How is MHR calculated in HIIT 4x4?

The app uses a commonly used formula of 220 minus your age in years to estimate MHR. It also suggests that a more accurate MHR can be found using a heart monitor during intense exercise.

### What happens if my heart rate falls out of the target zone?

If your heart rate deviates from the target interval range, HIIT 4x4 will issue warning chimes until your heart rate returns to the desired zone.

### What is the age rating for HIIT 4x4?

HIIT 4x4 has an age rating of 12+. This indicates it is suitable for users aged 12 and older.

### How often is HIIT 4x4 updated?

The latest version of HIIT 4x4 is 1.08, and it was last updated on September 20, 2024. This suggests regular updates to maintain functionality.

## Version history (last 5 releases)

### 1.09 — 2026-06-26

ios 27 support

### 1.08 — 2024-09-20

Start button moved to Settings screen to streamline operation.

### 1.07 — 2023-01-13

Added active calories to the workout

### 1.06 — 2022-09-13

Added Metric switch to Settings
Apple Watch Ultra support

### 1.05 — 2022-03-22

Enhanced support for 45 mm watch face

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## More apps by Eastridge Technology

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- [Hearts: Shoot the Moon](https://appshunter.io/ios/app/hearts-shoot-the-moon/id1547434423)

All apps by Eastridge Technology: https://appshunter.io/developer/392920417

## Related topics

[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 2026-07-05.*