Training by numbers
Training numbers are unusually honest about being estimates, and unusually often treated as facts. A heart rate zone, a one-rep max and a predicted marathon time are all approximations with known error bars.
The useful thing is not to distrust them but to know which way each one is wrong, and by roughly how much.
220 minus your age is a population average
The familiar formula gives a 35-year-old a maximum heart rate of 185. Individual maximums scatter around that by roughly twelve beats in each direction, which means the estimate could be out by more than a whole zone.
It is still worth having, because the alternative — an all-out maximal test — is not something most people should do casually. But it means the zone boundaries are soft, and it means chasing a specific number on a watch is chasing something invented.
A tested maximum, from a hard effort you have actually recorded, is worth far more than the formula. If you have ever finished a race flat out with a watch on, the highest reading is probably closer to the truth than 220 minus your age.
Zones, and the one everybody trains in by mistake
Using the Karvonen method — which works from heart-rate reserve, the gap between resting and maximum — a 35-year-old with a resting rate of 60 gets zone 2 from 135 to 148 and zone 3 from 148 to 160.
Almost all endurance benefit comes from zone 2: conversational pace, where you could hold a sentence without gasping. The common error is training everything in zone 3, which feels productive and is not — too hard to recover from properly, too easy to drive the adaptations that hard sessions produce.
That leaves most people doing a moderate amount of moderate work every day. The alternative that works is polarised: most sessions genuinely easy, a small number genuinely hard, and very little in the middle.
Karvonen gives higher targets than a plain percentage of maximum, so the two methods disagree by enough to matter. If a zone chart seems oddly easy, check which method produced it.
Age 35, resting 60 -> max 185 bpm
Zone 2 (endurance) 135-148 bpm <- most of your training
Zone 3 (tempo) 148-160 bpm <- where most people live
Zone 4 (threshold) 160-173 bpm
Work it out: Heart Rate Zone Calculator →
One-rep max: good to about ten reps
Lifting 100kg for five reps estimates a one-rep max of about 114.6kg. The two common formulas — Epley and Brzycki — give 116.7 and 112.5, and that four-kilogram spread is a fair picture of the uncertainty.
They agree closely at low reps and drift apart as reps rise, and beyond about ten reps the estimate flatters you badly, because what you are measuring stops being strength and starts being endurance and technique.
The useful direction is the other one. Rather than estimating a maximum you will never attempt, use it to set working weights: the same 100kg-for-five lifter should be handling around 91.7kg for sets of eight and 85.9kg for sets of ten. That is a training plan rather than a party trick.
Work it out: One Rep Max Calculator →
Race predictions assume you do not slow down
A 50-minute 10K is five minutes a kilometre, or 8:03 a mile. Held exactly, that pace gives a 1:45:29 half marathon and a 3:30:59 marathon.
Nobody holds it. Real pace fades with distance — typically by several per cent per doubling — so a marathon time derived from 5K pace is arithmetic rather than a prediction. The longer the extrapolation, the more optimistic it is.
Where the numbers are genuinely useful is close to the distance you actually trained for, and as a way of converting between pace and speed. A treadmill wants kilometres per hour; a watch wants minutes per kilometre. They are the same number upside down, and the conversion is the thing worth having on a page.
Work it out: Running Pace Calculator →
VO2 max is the best single number, and it is still an estimate
VO2 max is how much oxygen you can use per kilogram per minute at full effort, and it is the best laboratory measure of aerobic fitness there is. Every field estimate — including the ones on this site — is an approximation of a treadmill test.
A 35-year-old covering 2,600 metres in a twelve-minute Cooper test estimates around 46.8, which rates as good. The heart-rate method, which needs no maximal effort at all, puts the same person at 47.2 — close enough to be reassuring about both.
It responds well to training, and the least fit improve fastest. It also falls with age at roughly ten per cent a decade if untrained, and considerably less than that if you keep going. That second clause is most of the argument for training in middle age.
The Cooper test is a maximal effort and not something to attempt untrained. The heart-rate estimate exists precisely so that you do not have to.
Work it out: VO2 Max Calculator →
Questions
Is 220 minus age accurate?
As a population average, yes. For an individual it scatters by about twelve beats either way, which is more than a zone wide. A maximum you have actually recorded is worth much more.
What is zone 2 training?
Conversational pace — hard enough to be work, easy enough to hold a sentence. It is where most endurance adaptation comes from, and most people train above it without meaning to.
Why is training in zone 3 a problem?
It is too hard to recover from properly and too easy to produce the adaptations that hard sessions give. Doing everything there means a moderate amount of moderate work, which improves slowly.
How accurate is a one-rep max estimate?
Good to about ten reps, with the common formulas differing by a few per cent. Beyond ten reps it flatters you, because endurance and technique start doing the work instead of strength.
Can I predict my marathon time from a 10K?
Only loosely. Holding 10K pace for a marathon is arithmetic, not a prediction — real pace fades by several per cent per doubling of distance, so the extrapolation always runs fast.
What is a good VO2 max?
It depends heavily on age and sex, but for a 35-year-old man the high forties rates as good. What matters more than the level is the direction, since it responds well to training at any starting point.
Do I have to do a maximal test to estimate VO2 max?
No. The heart-rate method uses your resting and maximum rates and needs no hard effort at all. It exists for exactly that reason.