Accuracy · lab vs field
Lab vs Field Testing: How Accurate Are Free Zone Calculators?
Training-zone accuracy comes in three tiers. A free formula estimate is instant but rough (±10–12 bpm). A field test (a 20-minute FTP, a 30-minute LTHR, a 5k for VDOT) is far more accurate because it anchors to your physiology. A lab test (VO₂max, lactate threshold) is the gold standard, but expensive. Most athletes start with a formula and graduate to a field test.
The three tiers of accuracy
| Method | What it measures | Accuracy | Cost |
|---|---|---|---|
| Formula estimate | Age-based HRmax, %-of-max zones, population averages | Rough · ±10–12 bpm | Free, instant |
| Field test | 20-min FTP, 30-min LTHR, 5k for VDOT, 400/200 for CSS | Good · anchors to your physiology | Free · one hard effort |
| Lab test | VO₂max, lactate threshold, metabolic cart | Gold standard | Expensive · clinic visit |
When each is worth it
A formula estimate is the right starting point: it costs nothing, takes seconds, and gets a beginner training in roughly the right place. Once you're training consistently, a field test is the highest-value upgrade: one hard effort replaces a population average with your real threshold. A lab test earns its price when the stakes justify it: competitive athletes chasing marginal gains, anyone whose response to training is unusual, or athletes managing a health condition who want clinically measured numbers.
The honest limit of any calculator
Even a perfect lab test only gives you the zones. It can't tell you what to do in them day to day, how to sequence sessions across a week, when to push and when to back off, or how to adjust for accumulated fatigue, a poor night's sleep, illness, or a stressful week at work. That's the part no calculator solves. It takes coaching judgement applied to your week, your data and your goals.
From map to terrain
A calculator gives you the map; a coach helps you read the terrain.
TrainingZones hands you accurate zones for free, forever. When you want someone to turn those zones into a plan, and adapt it as life gets in the way, that's what Coach Kalle is for.