Accuracy · lab vs field
Lab vs Field Testing: How Accurate Are Free Zone Calculators?
Training-zone accuracy comes in three tiers. A formula estimate is instant but rough (±10–12 bpm). A field test (20-minute FTP, 30-minute LTHR, a 5k for VDOT) anchors to your physiology and is far more accurate. A lab test (VO₂max, lactate threshold) is the gold standard but costs money.
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
Start with a formula: free, instant, close enough for a beginner. Once you train consistently, a field test is the highest-value upgrade. One hard effort replaces a population average with your real threshold. A lab test pays off for competitive athletes or anyone managing a health condition.
The honest limit of any calculator
Even a perfect lab test only gives you the zones. It cannot tell you what to do in them today, how to sequence a week, or how to adjust for fatigue and poor sleep. That takes coaching judgement.
From map to terrain
A calculator gives you the map. A coach helps you read the terrain.
TrainingZones gives you accurate zones for free. When you want them turned into a plan that adapts as life gets in the way, that is Coach Kalle.