Every app below can time a Norwegian 4x4: 4 minutes hard, 3 minutes easy, four rounds. The differences show up in what they can tell you afterward — live heart rate, per-interval analysis, and whether your heart rate recovery is improving. Here's the honest breakdown, ourselves included.
The Best Norwegian 4x4 Apps for iPhone
Updated August 2026 · Feature claims verified against App Store listings. Reviewed quarterly.
| Feature | Viking 4x4 | Boreas | N4x4 | Norwegian 4x4 Protocol | Generic HIIT timers |
|---|---|---|---|---|---|
| Price | Free at launch | Free | Free | $5.99 | Free–$10 |
| Apple Watch live heart rate | Yes | Yes (basic) | No | No | Varies |
| Per-interval HR report | Yes | No | No | No | No |
| HR recovery (HRR) tracking | Yes | No | No | No | No |
| Voice coaching | Yes | Basic cues | Timer alerts | Timer alerts | Varies |
| Apple Health sync | Yes | Yes | No | Partial | Varies |
| History depth | Full history + recovery trends | Minimal | None | Basic log | Varies |
Viking 4x4
- Price
- Free at launch
- Apple Watch live heart rate
- Yes
- Per-interval HR report
- Yes
- HR recovery (HRR) tracking
- Yes
- Voice coaching
- Yes
- Apple Health sync
- Yes
- History depth
- Full history + recovery trends
Boreas
- Price
- Free
- Apple Watch live heart rate
- Yes (basic)
- Per-interval HR report
- No
- HR recovery (HRR) tracking
- No
- Voice coaching
- Basic cues
- Apple Health sync
- Yes
- History depth
- Minimal
N4x4
- Price
- Free
- Apple Watch live heart rate
- No
- Per-interval HR report
- No
- HR recovery (HRR) tracking
- No
- Voice coaching
- Timer alerts
- Apple Health sync
- No
- History depth
- None
Norwegian 4x4 Protocol
- Price
- $5.99
- Apple Watch live heart rate
- No
- Per-interval HR report
- No
- HR recovery (HRR) tracking
- No
- Voice coaching
- Timer alerts
- Apple Health sync
- Partial
- History depth
- Basic log
Generic HIIT timers
- Price
- Free–$10
- Apple Watch live heart rate
- Varies
- Per-interval HR report
- No
- HR recovery (HRR) tracking
- No
- Voice coaching
- Varies
- Apple Health sync
- Varies
- History depth
- Varies
Feature comparison as of August 2026. "Varies" reflects a category of apps rather than a single product.
1. Viking 4x4Our app
Built around one question: is the protocol working? Per-interval heart rate reports and 60-second heart rate recovery trends are the core of the app, not an afterthought.
2. Boreas
The closest competitor and a genuinely solid free timer — clean design, basic Apple Watch heart rate, and HealthKit saving. What it doesn't do is analyze: no per-interval breakdown, no recovery tracking, minimal history.
3. N4x4
A set-and-forget interval timer. If you want zero setup and zero data, it does the job — but it can't tell you anything about your heart.
4. Norwegian 4x4 Protocol
A paid timer with basic session tracking, best known for a Tim Ferriss blog mention. No live heart rate analytics or recovery measurement.
5. Generic HIIT timers
For apps like HIIT Timer or VO2Max Timer, the 4x4 is one preset among many. Fine for casual use; none are built around the protocol or its physiology.
The honest bottom line: if all you want is a well-made free timer, Boreas is good and we'll say so. If the reason you're doing the 4x4 is to raise your VO2 max and you want proof it's happening, that measurement layer — per-interval reports and recovery trends — is exactly the gap Viking 4x4 exists to fill.
SKÅL!
The 4x4 app that shows your heart getting stronger.
Launching soon on iPhone
Free at launch · iPhone · Apple Watch heart-rate support