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.
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.
Coming soon to the App Store
- 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.
- 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.
- Free & private
No account, no ads, no tracking. Workouts save to Apple Health if you want them to — your health data never leaves your device.