Four intervals of four minutes above 85% of max heart rate, three minutes of rest between each. The most-studied protocol for raising VO₂max — and the strongest single predictor of how long you live.
A regular interval timer counts down four minutes the moment you press start — whether your heart rate is at 60% or 90%. Two minutes of ramp-up means two minutes of “interval” that wasn’t actually at VO₂max. Sessions become non-comparable, progress untrackable.
The timer only counts when your HR is above 85% of max. Ramp up at your own pace; if you drop below the threshold mid-interval, the clock pauses until you climb back. Every session delivers exactly 4 × 4 minutes of true VO₂max work.
Higher than smoking status, higher than blood pressure, higher than diabetes. The Norwegian 4×4 is the most efficient way to move it. Stellar makes the protocol repeatable so the gains are measurable.
Three sources, one protocol. Pair a Polar strap, a Garmin watch, or AirPods Pro 3 — Stellar reads your heart rate live and runs the threshold logic regardless of where the beats come from.
Pair a Polar strap, a Garmin watch, or AirPods Pro 3 and start your first 4×4 in under a minute.