Zone 2 heart rate, explained

On the five-zone convention, zone 2 runs from 60 to 70 percent of maximum heart rate. Those edges are a training-industry convention with no paper behind them: the ACSM classification calls 57 to 63 percent light and 64 to 76 percent moderate, so zone 2 straddles two categories.

Work it out with the heart rate zone calculator

Zone 2 in beats per minute by age, computed two ways from the same maximum heart rate (Tanaka 2001). The Karvonen column assumes a resting heart rate of 60 bpm.
Age	HRmax, Tanaka	Zone 2 as 60-70% of HRmax	Zone 2 by Karvonen, resting 60
20	194	116-136	140-154
30	187	112-131	136-149
40	180	108-126	132-144
50	173	104-121	128-139
60	166	100-116	124-134
70	159	95-111	119-129

Where 60 to 70 percent came from

Nowhere in particular, and that is the honest answer. No paper derives the five ten-point bands that run 50, 60, 70, 80, 90, 100 percent of maximum; they are a training-industry convention, and this site labels them as one. The published thing in the neighbourhood is ACSM's classification of relative intensity, and its boundaries are different: very light below 57 percent, light 57 to 63, moderate 64 to 76, vigorous 77 to 95, near-maximal to maximal at 96 and above. Zone 2 as usually drawn therefore begins inside ACSM's light band and ends inside its moderate one. It is a slice of a chart, not a physiological boundary.

Two methods, two different zone 2s

Scaling a percentage of maximum heart rate and scaling heart-rate reserve give different bands from identical inputs. At 50, with a Tanaka maximum of 173 bpm, 60 to 70 percent of maximum is 104 to 121 bpm. Feed in a resting rate of 60 and run the same percentages through Karvonen and zone 2 becomes 128 to 139 bpm. The top edges are 18 beats apart. Neither is wrong: they are answers to different questions, and a chart that does not say which method it used cannot be reconciled with one that used the other.

And a third variable: which maximum you started from

The zone inherits every bit of uncertainty in the ceiling it is a percentage of. At 60 the three published equations give 166 bpm (Tanaka), 160 (Fox) and 153 (Gulati), which puts zone 2 at 100-116, 96-112 or 92-107 depending only on which equation the calculator chose for you. Sitting on top of that is the prediction error itself, 7 to 11 bpm, which is wider than the whole of zone 2 in some of those rows. A zone edge printed to the beat is false precision.

Why your watch disagrees with this page

Because platforms anchor zones to different things and all of them are defensible. Some scale a percentage of maximum heart rate. Some scale heart-rate reserve. Some anchor to a lactate threshold or a threshold heart rate measured in a test, which moves the boundaries again and is the version most endurance coaches mean. A device that has watched you train may also be estimating your maximum from observed data rather than your age. Two watches can put the same run in different zones and each be following a chart it can cite.

What zone 2 is not

It is not a fat-burning zone with a published definition. The proportion of energy drawn from fat is higher at lower intensities and the total energy used is higher at higher ones; both are true and neither makes a band special. It is also not a threshold you can locate on a watch to the beat. The useful reading of zone 2 is a broad region of conversational effort, cross-checked against how you feel rather than defended to the last digit.

Official sources

Frequently asked questions

What is my zone 2 heart rate?

On the five-zone convention it is 60 to 70 percent of your maximum heart rate. At 50, using Tanaka's maximum of 173 bpm, that is 104 to 121 bpm. Adding a resting rate of 60 and using Karvonen instead moves it to 128 to 139 bpm.

Are the five heart-rate zones an official standard?

No. No paper derives those particular ten-point edges. ACSM publishes an intensity classification with different boundaries - light 57 to 63 percent, moderate 64 to 76, vigorous 77 to 95 - and this site prints both tables side by side rather than implying they are the same scheme.

Why does my watch give a different zone 2?

Usually because it anchors zones to heart-rate reserve or to a measured threshold rather than to a percentage of maximum, or because it estimates your maximum from your training data rather than your age. All three choices are defensible and all three move the edges.

Is zone 2 the fat-burning zone?

No published classification defines a fat-burning zone. Fat supplies a larger share of energy at lower intensities, and higher intensities use more energy in total. Those two facts are both true and neither singles out 60 to 70 percent of maximum.

Should I use Karvonen or percent of maximum?

They answer slightly different questions, so the calculator shows both rather than choosing. Karvonen accounts for a low resting heart rate; percent of maximum ignores it. Karvonen bands always sit higher at the same nominal percentage.

Get a quarterly nudge to re-check your numbers

Four emails a year: a reminder to re-take your numbers, and what changed in the guidance behind these tools. No spam, unsubscribe any time.

Double opt-in: you will get one confirmation email and nothing else until you click it.