Guides
Understanding E, Vmax, P
What the three core parameters mean and how to interpret them.
TrueZone extracts three parameters from heart rate data. Together they define the complete physiological profile.
E — Endurance (0–100%)
What it measures: Aerobic endurance — the ability to sustain effort over time using fat oxidation and oxidative metabolism.
How to think about it: E tells you how far into the intensity spectrum you can go before relying heavily on glycolytic (anaerobic) metabolism. High E means your thresholds cluster near the top of your range, leaving a large aerobic base. Low E means early glycolytic reliance and faster fatigue.
Physiological basis: E = 2 x V0/V3 — defined by threshold alignment on the V-scale. It reflects fat-oxidation capacity, mitochondrial density, slow-twitch fiber ratio, and metabolic flexibility.
| E range | Population | Example |
|---|---|---|
| 10–30% | Sprint specialists, sedentary | Usain Bolt (~10%) |
| 40–55% | Untrained average | Typical healthy adult |
| 55–70% | Recreational runners | Regular joggers |
| 70–85% | Competitive endurance | Club runners, amateur cyclists |
| 85–100% | Elite endurance | Kipchoge (~100%), Ingebrigtsen (~94%) |
Trainability: E improves through consistent aerobic volume — long runs, tempo work, zone 2 training. Changes occur over months and years.
Vmax — Maximum Speed
What it measures: The absolute maximum speed — the fastest this person can run (or the highest power output for cycling), including both aerobic and anaerobic contributions.
How to think about it: Vmax is your neuromuscular speed ceiling. It determines how fast you can go, while E determines how long you can sustain fractions of that speed.
Units: Vmax is returned in m/s. Multiply by 3.6 for km/h.
| Vmax (km/h) | Level | Example |
|---|---|---|
| 20–24 | Recreational | Casual joggers |
| 24–28 | Competitive | Club runners |
| 28–34 | Advanced | National-level |
| 34–40 | Elite distance | Ingebrigtsen (~34), Kipchoge (~33) |
| 40–46 | Elite sprint | Bolt (~46), van Niekerk (~44) |
P — HRmax (bpm)
What it measures: The model-predicted maximum heart rate — determined geometrically from submaximal heart rate kinetics.
How to think about it: P anchors the heart-rate axis. It's the ceiling of the cardiovascular response. Unlike age-based formulas (220-age), P is measured from your actual data and accounts for individual variation, medication effects, and fitness state.
Why it matters: All HR zones, thresholds, and metabolic calculations scale from P. An inaccurate HRmax cascades into wrong zones. TrueZone derives P from submax data — no maximal test required.
Typical range: 150–220 bpm. Varies with age, genetics, and fitness. Not directly trainable — largely determined by cardiac structure.
How the parameters interact
The three parameters are independent:
- E controls threshold alignment and fatigue resistance
- Vmax controls absolute speed/power capacity
- P controls the heart rate scale
Two athletes with the same VO2max can have very different E values — one may be a durable, efficient runner (high E) while the other has high capacity but poor fatigue resistance (low E). This is why TrueZone separates capacity (Vmax/P) from efficiency (E).
PrimeScore — a universal fitness index
PrimeScore combines E and Vmax into a single 0–10 fitness index:
PrimeScore = (Vmax + V0) / k
where k is sport-specific (4.5 for running). World record holders from 100m to marathon all converge near PrimeScore = 10, despite vastly different E and Vmax profiles. This makes PrimeScore a fair, distance-neutral, sport-agnostic fitness metric.
PrimeScore+ normalizes PrimeScore for age and sex, enabling direct comparison across populations.