The Norwegian 4x4: the 38-minute interval session that raises your VO2 max

What one session looks like

• Warm-up: 5 minutes of light cardio at 50-60% of your maximum heart rate (HRmax).
• Interval 1: 4 minutes at 90-95% HRmax.
• Recovery 1: 3 minutes of active recovery at 60-70% HRmax. Keep moving; never stop.
• Repeat for intervals 2, 3 and 4, each followed by its 3-minute recovery.
• Cool-down: 5 minutes of light cardio.

Total: 38 minutes, of which 16 are genuinely hard. Four minutes is long enough to reach near-maximal oxygen uptake, three minutes lets you recover partially while your metabolism stays elevated, and four rounds is enough stimulus to adapt. The full guide suggests stretching the warm-up and cool-down to 10 minutes each when you have the time.

Where it comes from

The protocol was developed at the Norwegian University of Science and Technology (NTNU), where the group around Jan Helgerud, Jan Hoff and Ulrik Wisløff showed that four-minute intervals at 85-95% HRmax improved VO2 max more than moderate continuous training, in healthy adults and in cardiac patients. Dr Rhonda Patrick and Dr Peter Attia later popularised it as the gold standard for building the aerobic ceiling.

Find your zones first

Everything in the protocol is a percentage of your maximum heart rate, so work that out before the first session. norwegian4x4.com uses the HUNT formula from a 3,320-person NTNU study, HRmax = 211 - 0.64 × age, which beats the old "220 minus age" rule: that one can be 10-20 beats off, and up to 40 in older adults.

How to run the intervals

• Start controlled. Interval 1 should feel almost too easy for the first minute; going all-out early is the classic beginner mistake.
• Interval 3 is usually the hardest. Break it into one-minute chunks.
• Breathe in rhythm (2 in, 2 out, or 3 and 3). Check the clock at halfway, not constantly.
• Recovery is active: slow right down but keep moving. Stopping completely reduces the effect; staying too hard means you will not recover for the next round.
• Watch your heart rate, not just perceived effort, and log your average per round. Over time the goal is less drop-off in rounds 3 and 4.

Any cardio works

The protocol is sport-agnostic. Guidance from the site by modality:

The 12-week program

Weeks 1-4 follow the guide's week-by-week beginner progression, with its 10-minute warm-up and cool-down. Weeks 5-12 follow its intermediate plan: the classic 38-minute session, two sessions a week as the minimum with an optional third on Saturday. Already fit and doing HIIT? The guide says start straight at the standard protocol, so begin at week 5.

• Keep at least 48 hours between sessions, and never do more than four a week.
• If a week feels too hard, repeat it before moving on. There is no rush.
• Every four weeks, retest: resting heart rate, your device's VO2 max estimate, a 12-minute Cooper test or a 2,000 m row.

Safety

• Check with a doctor first, especially if you are over 40, have a heart condition, hypertension or diabetes, are pregnant, or take beta blockers.
• Stop immediately for chest pain or pressure, dizziness, unusual shortness of breath, an irregular heartbeat or nausea.
• Over 50: warm up 12-15 minutes, prefer incline walking or low-impact machines, allow extra recovery, and add two strength sessions a week for bone health.
• Sleep 7-9 hours, hydrate, eat something light 1-2 hours before, and refuel with protein and carbs within 30-60 minutes after.

Sources

This article follows norwegian4x4.com, its beginner's guide, FAQ, calculator and the free Complete Norwegian 4x4 Workout Protocol Guide (v1.1, February 2026). JustGains is not affiliated with or endorsed by norwegian4x4.com or NTNU.