Viking 4x4

4 minutes hard. 3 minutes easy. Repeat 4 times. Finish strong. Viking 4x4 is the interval coach built around one protocol — the Norwegian 4x4 — the workout researchers used to raise VO2 max faster than steady cardio and, in a two-year trial, reverse decades of cardiac aging. No bloated workout library. No guesswork. Just the protocol, coached by your heart rate, with proof at the end that it is working. HOW IT WORKS • Set your session — warm-up, four hard intervals, easy recoveries, cool-down. The 45-minute default is the exact protocol from the research. • Press Start — your Apple Watch app launches itself and streams live heart rate to your iPhone. No fiddling with the Watch mid-workout. • Follow the coach — voice cues and haptics tell you when to push, when to ease off, and when the next interval is coming. Never look at a screen while you train. • SKÅL — every session ends with your interval report: peak heart rate, recovery heart rate, and your HRR-60 for each round. THE NUMBER THAT MATTERS Heart-rate recovery — how far your heart rate drops in the 60 seconds after each interval — is one of the strongest everyday signals of cardiovascular fitness. Viking 4x4 measures it on every round and tracks it across sessions, so you can literally watch your heart get stronger week after week. BUILT FOR THE PROTOCOL • Live heart-rate zones with a 85–95% work target that lights up when you are in range • Two-level session timeline so you always know what is coming • ±30-second adjustments and pause without losing your place • Running, cycling, rowing, elliptical, stair climber — indoor or outdoor • Workouts, heart rate, and calories saved to Apple Health and your Activity rings • Full history with per-interval reports • Screen stays awake, cues keep coming with your phone in your pocket WHY THE 4x4 In the landmark Helgerud study, eight weeks of 4x4 intervals improved VO2 max by about 7% — roughly double the gain from steady jogging. Cardiorespiratory fitness is among the best-known predictors of healthspan, which is why longevity experts keep pointing to this exact protocol. Learn more, with sources, at viking4x4.app. APPLE WATCH Viking 4x4 includes an Apple Watch companion that records the workout on your wrist and mirrors it to your phone in real time. Works with Apple Watch Series 4 and later. You can also use the app as a heart-rate-free interval timer without a Watch. PRICING Your first full 4x4 is free. Unlimited Workouts is available as a monthly ($6.99) or yearly ($29.99) auto-renewing subscription. Payment is charged to your Apple ID account at confirmation of purchase. Subscriptions renew automatically unless cancelled at least 24 hours before the end of the current period, and can be managed in your App Store account settings. Terms: https://viking4x4.app/terms Privacy: https://viking4x4.app/privacy Viking 4x4 is a training tool, not medical advice. Talk to your doctor before starting high-intensity exercise.