Methodology · how we calculate
Methodology & Sources: How We Calculate
Every formula on TrainingZones is a unit-tested function tied to a primary source. Each model below comes from the reference that defined it.
How we calculate
Each formula is a small deterministic function: same inputs, same zones. Below is every model family on the site and its primary source.
| Model | Primary source |
|---|---|
| Max heart rate | Tanaka et al. 2001; Gulati et al. 2010 (women) |
| %HRmax & Karvonen (heart-rate reserve) | Karvonen et al. 1957; ACSM Guidelines |
| Lactate-threshold heart rate (LTHR) | Friel, Training Bible; Allen & Coggan |
| MAF aerobic heart rate (180 Formula) | Maffetone, The Big Book of Endurance Training |
| FTP & power zones | Allen & Coggan, Training and Racing with a Power Meter |
| Critical Power | Monod & Scherrer 1965; Jones et al. |
| VDOT & running paces | Daniels & Gilbert 1979; Daniels' Running Formula |
| Critical Swim Speed (CSS) | Wakayoshi et al. 1992 |
| Polarized / 80-20 distribution | Seiler & Kjerland 2006 |
| Rowing UT2–AN zones | British Rowing; Concept2 |
| Intensity zones I1–I5 | Norwegian Olympic federation; Seiler & Tønnessen |
| Ski-mountaineering VAM | Vertical ascent rate (meters climbed per hour) |
Accuracy & testing
Each formula ships with an automated test asserting reference values from its source. Tanaka's 208 − 0.7 × age must return 187 bpm at age 30. Daniels' equations must reproduce the VDOT tables. If a refactor breaks a number, the test fails before the page ships.
Limitations
Every formula here is an estimate. Age-based equations carry a standard deviation of roughly 10–12 bpm. Field tests, and above all lab tests, are more accurate. See lab vs field testing for how the three tiers compare.
Freshness commitment
Every formula and source is reviewed at least twice a year. We revisit formulas and sources at least twice a year and show the review date here.
Last reviewed: 6 September 2026
Corrections welcome
Spot a formula, source or value that looks wrong? Email mf.nevs@olleh with the page and the reference. We will check it and fix it.