Crescendo 4×4: Norwegian HIIT

The Norwegian 4×4 protocol builds VO₂max like almost nothing else — four 4-minute pushes at 85–95% of max heart rate. The problem? Starting there feels like hitting a wall. Crescendo removes the wall. You start with intervals as short as 30 seconds and climb a structured on-ramp, level by level, until the full 4×4 is yours. Progress is earned, never rushed — the app can even gently hold a level-up if your recovery data suggests you need it. GUIDED SESSIONS • Voice cues for every phase — works with the screen locked, music keeps playing • Warm-up, four work/recovery cycles, cool-down: fully guided • Date-anchored timing that never drifts PERSONAL BY DESIGN • Heart-rate zones from your real max HR — from Apple Health or set manually • A conservative level-up gate that watches your resting HR and VO₂max trends • Start where YOU are: from 30-second familiarization runs to the full protocol APPLE WATCH + HEALTH • Send any session to your Watch and run it from the native Workout app • Watch-run sessions count toward your progress automatically • Phone sessions save to Apple Health (your choice) HONEST BY DEFAULT • Free. No account. No ads. No streak guilt. • Your health data stays in Apple Health — we don't collect it. High-intensity interval training is demanding. If you're unsure about your health, check with your doctor before starting.