The Norwegian 4×4 protocol is the most efficient way to raise VO₂ Max — the #1 predictor of how long you'll live. All you need is AirPods Pro 3. No gym required.
AirPods Pro 3 or Powerbeats Pro 2 read your heart rate through the in-ear sensor. That's your entire setup. No chest strap, no gym, no extra hardware.
The app tells you when to push (Zone 4) and when to recover (Zone 2). No guessing, no clock-watching.
4 intervals, 3 recoveries, warm-up and cool-down. Every session pushes your VO₂ Max higher. Every point gained = 13% lower mortality.
VO₂ Max measures how much oxygen your body can use under stress. It's the reason you get winded on stairs at 45, can't keep up with your kids at 50, and feel decades older than you are. A study of 122,007 adults (Mandsager et al., JAMA 2018) found it's a stronger predictor of death than smoking, diabetes, or heart disease.
After 30, you lose ~10% per decade. The decline is silent — until you notice you can't do what you used to. But it's reversible.
Low cardiorespiratory fitness carries a 5× higher mortality risk than high fitness — worse than coronary artery disease (1.3×), worse than smoking (1.4×). This isn't fringe science. It's the largest study ever done on fitness and mortality (Mandsager et al., JAMA 2018).
Helgerud et al. (Medicine & Science in Sports & Exercise, 2007) tested the Norwegian 4×4 protocol and measured a 46% VO₂ Max increase in sedentary subjects over 8 weeks. Every 1-MET increase cuts mortality risk by 13%. Going from the bottom 25% to average fitness has the same survival benefit as curing a chronic disease.
Open Apple Health → Browse → Heart → Cardio Fitness. If you have VO₂ Max data there, we read it automatically and show you exactly where you stand — and what you need to do to climb higher.
| Age 40–49 | Below 29 = danger zone |
| Age 40–49 | 29–39 = average |
| Age 40–49 | Above 39 = strong |
| Age 50–59 | Below 26 = danger zone |
| Age 50–59 | 26–36 = average |
| Age 50–59 | Above 36 = strong |
The Norwegian 4×4 is the most studied, most efficient protocol for raising VO₂ Max. We track your 90-day trend from Apple Health so you can watch the number climb. Every point you gain buys you time.
iOS 26 turns your AirPods Pro 3 into a real-time heart rate monitor via the in-ear sensor. Powerbeats Pro 2 work too. We're the first interval training app built around it. Pop them in, press start, and your heart rate drives the entire workout.
Real-time heart rate with automatic Karvonen zone calculation. Your zones, personalized to your age and resting HR. See exactly where you are — and where you need to be.
Voice cues through your AirPods tell you when to push and when to recover. No guessing, no clock-watching. Just follow the beeps.
Every session gets a quality score based on time-in-zone accuracy. Were you in Zone 4 when you needed to be? We'll tell you — and show you how to improve.
Watch your VO₂ Max climb week over week with a 90-day trend chart pulled from Apple Health. Every point you gain = 13% lower mortality risk. That's not a motivational poster — it's peer-reviewed data.
Apple Fitness+ doesn't coach intervals. Strava doesn't read your heart rate zones. Generic HIIT timers don't know your VO₂ Max. We do one thing — the Norwegian 4×4 protocol — backed by 15 years of cardiology research. Tanaka max HR, Karvonen HRR zones. No bro-science.
Your AirPods are the heart rate sensor. Everything else is optional.
AirPods Pro 3 and Powerbeats Pro 2 read your heart rate through the in-ear optical sensor (iOS 26+). They're the core of the experience — live HR zones, voice coaching cues, and real-time feedback all through the earbuds you already own.
Add your Watch as a second screen: real-time HR arc gauge, zone haptics, interval countdown, and phase coaching on your wrist. Nice to have, not required.
You'll be out of breath by interval 2. Your quality score: 50–60%. That's normal. Everyone starts here. The app tracks your heart rate so you can focus on just moving.
You'll finish all 4 intervals in zone. Quality: 75%+. Your resting heart rate drops. Your VO₂ Max starts climbing. You'll notice stairs feel different.
The original Norwegian study measured 46% VO₂ Max improvement at this point. You'll feel 10 years younger. The training calendar fills up with green dots. You're hooked.
Unlock advanced features with a free 7-day trial. No credit card, no account.
Monthly grid showing every workout day, color-coded by quality. Tap any day to see interval breakdowns. Track consistency at a glance.
Generate a branded PDF report after each session — quality scores, interval stats, zone targets. Share with your coach or keep for your records.
Modify interval count (2–6), duration (3–5 min), recovery time, warm-up and cool-down. Build your own protocol variant.
Free users see 3 recent sessions. Pro unlocks your full training history — every session, every score, forever.
We don't have servers. We don't have accounts. All workout data lives in Apple Health and on your phone. Period.
AirPods Pro 3 and 40 minutes. The protocol that adds years to your life.
Start Your First Workout — FreeNo account. No credit card. No gym. Just AirPods and go.