Explainer
The science, without the hand-waving
Six short sections: what VO₂max is, how we compute your zones, why adherence is the real problem, and where music actually helps.
VO₂max is the number that moves the needle
Maximal oxygen uptake is how much oxygen your body can use per kilogram per minute at full effort. It integrates lung, heart, blood and mitochondria into one figure, and in large cohort studies it separates risk groups more sharply than smoking, hypertension or diabetes. Crucially it is trainable at any age.
Zones are arithmetic, not vibes
We predict maximum heart rate with Tanaka (208 − 0.7 × age), which is better behaved across ages than 220 − age, then apply the Karvonen heart-rate-reserve method so your resting heart rate shifts the bands. A fit 50-year-old and an unfit 50-year-old get different targets from the same zone.
Most gains come from being bored correctly
The highest-yield prescription is unglamorous: long, easy zone-two work plus a small dose of hard intervals. The failure mode is not ignorance, it is drift — going too hard on easy days and too easy on hard days. That is a compliance problem, and compliance responds to sound.
Tempo entrainment is the lever
Movement synchronises to beat. When the track's BPM sits at a whole-number relationship to your target heart rate, cadence and effort settle into the band without conscious pacing. When you drift high, the music does not chase you — it holds the anchor and pulls you back.
Generation, not a playlist
A playlist can only approximate your prescription. A generative model can render the exact tempo map for the exact six phases of your session, which is why every render is unique, watermarked and traceable back to the physiology that produced it.
What this is not
Not a medical device, not diagnostic, not a substitute for clinical testing. Estimates carry ±10–15% error. If you have cardiac symptoms, see a clinician before training hard.
Zone reference
Zone 1 — Recovery50–60% of heart-rate reserve
Blood flow and repair. Conversation stays effortless.
Zone 2 — Aerobic base60–70% of heart-rate reserve
Mitochondrial density and fat oxidation. The healthspan zone.
Zone 3 — Tempo70–80% of heart-rate reserve
Sustained power. Comfortably hard, speech in short phrases.
Zone 4 — Threshold80–90% of heart-rate reserve
Lactate clearance. Raises the ceiling you can hold.
Zone 5 — VO₂max90–100% of heart-rate reserve
Maximal oxygen uptake. Short, sharp, fully committed.