Z2/4×4 Trainer

Z2/4×4 Trainer turns the two most effective endurance methods — easy Zone 2 base work and high-intensity Norwegian 4×4 intervals — into a simple daily plan built around YOUR heart rate.

WHAT YOU GET • Daily and weekly Zone 2 prescriptions at 60–70% of your max heart rate to build your aerobic base. • Norwegian 4×4 sessions: four 4-minute intervals at 85–95% of max heart rate, with 3-minute recoveries — the protocol used to boost VO2 max. • Weekly health-maintenance and weight-loss targets to keep you consistent. • Personalized zones from your max heart rate (220 − age), which you can override if you know your true max.

WORKS WITH APPLE HEALTH • Pull in your heart rate, resting heart rate, active energy, body weight, and past workouts — or enter everything manually. Your choice. • Completed Zone 2 and 4×4 workouts are saved back to Apple Health so all your training lives in one place.

IPHONE + APPLE WATCH • Plan and review on iPhone; train with your zones on your wrist.

PRIVATE BY DESIGN • 100% on-device. No account, no sign-up, no server. • Nothing you enter or that we read from Apple Health ever leaves your device. • No ads, no analytics, no tracking, no third-party SDKs. • Your Health data is never used for advertising — ever.

WHO IT'S FOR • Runners, cyclists, rowers, and anyone doing cardio who wants structure instead of guesswork. • Beginners building a base and experienced athletes adding VO2-max work.

FREE + AN OPTIONAL ONE-TIME UPGRADE • Everything above is free: guided workouts on iPhone and Apple Watch, plans, zones, Apple Health sync. • One optional one-time purchase (Pro) unlocks the deeper coaching analysis: full readiness breakdown, overtraining guard, adaptive weekly progression, VO2-max trend, and CSV/JSON export. No subscription.

Z2/4×4 Trainer is a fitness and training tool, not a medical device. It does not diagnose, treat, or prevent any disease. Talk to a healthcare professional before starting a new exercise program.