VO2 max is the single strongest predictor of how long you'll live — and how well.
N4x4 delivers the exact protocol proven to raise it.
"Cardiorespiratory fitness, as measured by VO2 max, is the single greatest predictor of lifespan — more than smoking, more than diabetes, more than heart disease."
— Dr. Peter Attia, MD · Author of Outlive
VO2 max drops roughly 10% per decade after age 25 without targeted training. By 65, most sedentary adults have lost nearly half their peak capacity.
A landmark study of 122,000 patients found that being in the bottom 25% for VO2 max carried a higher mortality risk than smoking, hypertension, or diabetes.
High-intensity interval training is the most efficient way to raise VO2 max — far more than steady-state cardio. The Norwegian 4x4 is the gold standard.
Developed at the Norwegian University of Science and Technology. Refined over 30 years of research. Used by elite athletes and longevity researchers worldwide.
During the 4-minute work intervals, push to 85–95% of your maximum heart rate. You should not be able to hold a conversation. If you can, push harder.
Biochemist and longevity researcher Dr. Rhonda Patrick has covered the Norwegian 4x4 protocol extensively. Watch this 90-second clip.
Dr. Rhonda Patrick has no affiliation with N4x4.
N4x4 does one thing: guides you through the protocol flawlessly, every time. No gamification BS. Just you and the work.
Audio cues tell you exactly when to push, when to recover, and how many intervals remain. No staring at your screen. Eyes forward, head down.
A clean visual countdown shows your interval progress. Know at a glance where you are in the work and rest phases.
Your workout lives on your lock screen and in the Dynamic Island. Interval timer always visible, even when you're in another app or your screen locks.
Track your weekly training streak. Celebrate milestone sessions at 1, 5, 10, 25, 50 and 100 completed workouts. Consistency made visible.
After every session, learn what just happened in your body — EPOC, mitochondrial biogenesis, VEGF, BDNF. Science that keeps you motivated.
Running, cycling, rowing, swimming, treadmill — any exercise that gets your heart rate up works. The app doesn't care. Your cardiovascular system doesn't either.
High-intensity intervals create excess post-exercise oxygen consumption (EPOC). Your metabolism stays elevated for up to 24 hours after the session ends.
HIIT triggers mitochondrial biogenesis — your muscle cells grow more mitochondria. More mitochondria means more energy, better endurance, and slower aging at the cellular level.
Intense intervals spike VEGF (vascular endothelial growth factor), stimulating angiogenesis — the growth of new capillaries. Better circulation means better oxygen delivery to every organ.
High-intensity cardio releases BDNF — brain-derived neurotrophic factor. It's been called "Miracle-Gro for the brain." Associated with better memory, sharper thinking, and protection against cognitive decline.
N4x4 was built because this protocol deserves to be accessible to everyone. It's a gift from one health-obsessed developer to the world.
Your workout is not an inventory slot.
Open the app. Start training. Done.
Your data stays on your device.
Just the protocol. Just the science.
Your cardiovascular system doesn't know if you're on a treadmill or a mountain trail. If your heart rate is in the zone, the protocol is working.
33 minutes. Once a week. The research is clear. The protocol is proven. The only question is whether you'll start.