Heart rate training gets a bad reputation mostly because people ask it to do a job it is not good at. Used for the one thing it is genuinely excellent at, it is one of the most useful tools an endurance athlete has.
The job zones are good at
Keeping easy runs easy. The single most common error in amateur endurance training is that easy runs are run slightly too hard, which quietly turns them into moderate runs that produce fatigue without producing much adaptation.
A heart rate ceiling is an honest, unarguable brake. It does not care that the pace feels embarrassing or that someone just overtook you.
The job they are bad at
Prescribing hard sessions. Heart rate lags effort by a minute or more, drifts upward across a long session at constant effort, and moves around with heat, caffeine, sleep and stress. By the time your heart rate reaches the target for a three-minute interval, the interval is nearly over.
For hard sessions, use pace, power, or how it feels. All three respond instantly.
Where the numbers come from
The familiar 220-minus-age formula is a population average with a very wide spread around it. Plenty of people sit ten or fifteen beats either side. Building your training zones on it is building on a guess.
Better options, in ascending order of accuracy:
- The talk test. If you cannot speak a full sentence, it is not an easy run. Free, and surprisingly hard to argue with.
- A field test. A 20 to 30 minute all-out effort, with average heart rate over the final 20 minutes taken as a rough threshold marker.
- A lab test. The accurate option, if you have access to one.
A simple, usable model
- Easy — conversational. The large majority of your weekly volume lives here.
- Steady — comfortably hard, sentences but not paragraphs.
- Threshold — hard, sustainable for roughly an hour at maximum.
- Hard — interval effort. Do not use heart rate to steer this.
Four descriptions, no decimal places. For most athletes that is more useful than a seven-zone model with boundaries derived from a number nobody measured.
When to ignore it entirely
In heat, at altitude, when ill, when under-slept, and in the first ten minutes of any run. In all of those, the number is telling you about your circumstances rather than your effort.
