The Norwegian 4×4 — starting at 30 seconds.

Four 4-minute pushes at 85–95% of max heart rate build VO₂max like almost nothing else. Crescendo removes the wall: begin with 30-second intervals and climb to the full protocol, one earned level at a time.

Start at 30 seconds
The Norwegian 4×4 builds VO₂max like almost nothing else — but starting there feels like hitting a wall. Crescendo begins with intervals as short as 30 seconds and climbs a structured on-ramp, level by level, until the full 4×4 is yours.
Guided by voice
Warm-up, four work/recovery cycles, cool-down — every phase announced by voice cues that keep working with your screen locked and your music playing.
Lock Screen & Dynamic Island
Your active session lives on the Lock Screen and in the Dynamic Island (iOS 17+; Dynamic Island on compatible models). Check your phase, interval, target heart-rate zone, and live countdown at a glance.
Available in 4 languages
Complete voice coaching, interface, and health setup in English, Polish, German, and Spanish — matching your device language automatically.
Heart-rate zones made for you
Your 85–95% work zone is computed from your real max heart rate — read from Apple Health with your permission, or set manually. No silent defaults.
Send it to Apple Watch
Push any session to your Watch and run it from the native Workout app, with per-interval heart-rate targets. Watch-run sessions count toward your progress automatically.
Progress you earn
Level up after consistent sessions — never rushed. If your recovery data suggests you need more time, Crescendo can gently hold a level-up. Never stuck, never guilt-tripped: no streaks, no shame mechanics.
Private by design
No account, no ads, no tracking. Workouts save to Apple Health if you want them to — your health data never leaves your device.

New to Norwegian 4×4? Start here.

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Frequently asked questions

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What is the Norwegian 4x4 workout?

The Norwegian 4×4 is a high-intensity interval protocol from NTNU in Norway: four 4-minute work intervals at 85–95% of your maximum heart rate, each followed by 3 minutes of easy recovery, plus a warm-up and cool-down — about 40 minutes total. It is the most-studied HIIT protocol for improving VO₂ max, with research showing gains of roughly 7–10% in eight weeks.

Learn more: The Norwegian 4×4 protocol, explained →

Is the Norwegian 4x4 suitable for beginners?

The full protocol is not a beginner workout — 16 minutes near maximal heart rate assumes an aerobic base. But its structure scales down beautifully: start with 1-minute work intervals, and build length and count over six to ten weeks. Crescendo 4×4 exists precisely for this — a progressive couch-to-4×4 on-ramp that no other 4×4 resource offers.

Learn more: The couch-to-4×4 on-ramp →

What heart rate should 4x4 intervals be at?

Work intervals target 85–95% of your maximum heart rate, reaching the top half of that range by each interval’s end; recoveries sit around 60–70%. Estimate your max with the Tanaka formula (208 − 0.7 × age) rather than 220-minus-age — or use a genuinely measured max if you have one.

Learn more: Finding and holding your 4×4 zones →

How often should I do Norwegian 4x4 workouts?

Twice a week, at least 48 hours apart, for eight weeks — that is the researched dose behind the famous VO₂ max results. More hard sessions is not better: the adaptations happen during recovery, and a third or fourth weekly 4×4 typically degrades quality before it adds fitness. Spend extra energy on easy aerobic work instead.

Learn more: Dosage and a realistic results timeline →

Does Crescendo 4x4 work with a locked screen and music?

Yes. Every session is voice-coached — interval starts, halfway calls, recoveries, and countdowns — and the cues keep firing with your iPhone locked in a pocket or armband. Your music ducks briefly under each cue and comes right back; it never stops. On iOS 17+, Live Activities and the Dynamic Island (on supported models) show your live phase, interval count, target heart-rate zone, and countdown directly on your Lock Screen.

High-intensity interval training is demanding by design. If you're unsure about your health, check with your doctor before starting — and start low: that's what the on-ramp is for.