Workout Heart Rate Zone Calculator

It is the heart rate at the highest intensity you can sustain while lactate production and clearance stay roughly in balance. Above it, blood lactate climbs and the clock starts on how long you can hold the effort. It matters for training because it is a physiological landmark that moves with fitness, unlike maximum heart rate, which is largely fixed and falls slowly with age. Training raises your threshold as a percentage of maximum, which is precisely why zones anchored to it track your fitness and zones anchored to age do not.

Warm up thoroughly, then run or ride 30 minutes alone at the hardest pace you can hold evenly, and take your average heart rate for the final 20 minutes only. That average is your LTHR with no multiplier applied. Discarding the first 10 minutes matters because heart rate lags effort at the start and including the ramp-up would drag the average down. Do it solo — racing someone changes your pacing and therefore your result.

Because they are measuring different things. A well-paced 20-minute maximal effort is run above true threshold — you can hold more for 20 minutes than you could for an hour — so the average is discounted by about 5% to estimate the sustainable figure. The 30-minute protocol already handles this by discarding the first 10 minutes and using only the settled portion of a longer effort. Applying the multiplier to a 30-minute result would double-count the correction and set every zone too low.

Because your threshold heart rate genuinely differs between them, usually by 5 to 15 bpm, and because Friel publishes different boundary percentages for each. Running recruits more muscle mass in a more upright posture, which drives a higher heart rate at the same relative effort. The practical consequence is that carrying a running LTHR onto the bike will set your cycling zones too high and quietly turn easy rides into moderate ones.

An age-based calculator estimates your maximum heart rate from a population regression and takes percentages of that. This page uses a number you measured, and never touches age at all except to show you the comparison. The difference is often large — commonly 10 to 20 bpm at the top of the aerobic zone — because the age formula carries a standard deviation of about 7 bpm before you apply any percentage to it. Our age-based page is the right tool if you have not tested; this one is the right tool if you have.

Friel splits the top of the range because three quite different sessions live up there. 5a, at 100 to 102% of threshold, is the threshold work itself. 5b, at 103 to 106%, is aerobic capacity — the classic VO2 max interval. 5c, above 106%, is anaerobic capacity, where efforts are measured in seconds and heart rate stops being a useful guide because it cannot respond fast enough. Collapsing them into one zone loses the distinction between a 20-minute tempo and a 40-second hill sprint.

The polarised model says roughly 80% of your sessions should be easy — Zone 1 and Zone 2 — with the remaining 20% genuinely hard. Note that this is a distribution of sessions, and the point is as much about what it excludes as what it includes: the moderate middle. The risk of aiming for a fixed percentage is that people push easy runs up to the top of Zone 2 to make the number, which defeats the purpose. Easy should feel easy.

Every 6 to 8 weeks during consistent training, and after any block that materially changed your fitness. Threshold heart rate as a raw number moves less than you might expect — what improves is the pace or power you can hold at it — but zones set from a stale test drift out of alignment. Do not test while ill, in unusual heat, or within a few days of a hard race.

Use the same device for the test and for the training, which matters more than which one you pick. Chest straps measure electrical activity and are generally more accurate at high intensity and in the cold; wrist optical sensors measure blood flow and are more prone to error during hard efforts, in cold weather, and where the strap moves. Mixing devices between the test and daily training introduces a systematic offset into every zone.

Not without medical advice. Beta blockers suppress heart rate at every intensity, including maximum, so both the tested threshold and every zone derived from it are shifted by an amount specific to your medication and dose. The zones would still be internally consistent with your own tested number, which is an advantage of the threshold method over the age method, but the effort those numbers represent is not the standard one. Speak to your clinician before using heart rate to govern training intensity.

Cardiac drift. Working muscle and skin compete for blood flow when you need to dissipate heat, so stroke volume falls and heart rate rises to maintain output at the same workload. Dehydration compounds it over a long session. The practical implication is that on hot days your zones will report a harder session than your legs did, and pace or power is the more reliable guide. This is a real limitation of heart-rate-governed training, not a fault in the boundaries.

No, but it is the one people occupy by accident. Tempo work in Zone 3 has a legitimate place in a plan, particularly for longer-distance racing where sustained moderate effort is the specific demand. The problem is unintentional Zone 3: easy runs that creep up into it accumulate fatigue without delivering either the recovery of Zone 2 or the stimulus of Zone 4 and above. Time in Zone 3 should be a decision you made, not a place you drifted to.

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It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.

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