Heart-rate zones guide how hard you train
High confidence
Heart-rate zones sort effort into bands set by a share of your maximum heart rate. For most people they give a simple, dependable way to judge how hard they are working. They get more accurate when you set them from a maximum you have actually measured, not one guessed from your age.
Why it works
As you work harder, your heart rate climbs in step with how much oxygen your body uses. That link holds steady across a wide range of efforts. So a percentage of your maximum heart rate (or of your heart rate reserve, the gap between resting and maximum) gives a handy stand-in for how hard you are working, even though it only roughly lines up with any one person's aerobic and anaerobic thresholds.
The evidence
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In 48 adults with metabolic syndrome (mean age 44), the researchers measured each person's heart rate at the first ventilatory threshold (the point where breathing starts to climb faster than effort, averaging 113 bpm) and compared it against target zones built from three common max-heart-rate equations. The best match came from taking 35% of heart rate reserve using the Fox equation, which landed almost exactly on the threshold (mean difference of just 0.35 bpm, agreement score 0.86). When a measured peak heart rate was available but breathing gas analysis was not, 40% of heart rate reserve or 70% of peak heart rate came closest. Targets of 40 to 45% of heart rate reserve from the prediction equations overshot the threshold, while 55 to 60% of predicted max fell well below it.
n=48
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Using measured maximal heart rate from 3,320 healthy adults across a wide age range (the HUNT Fitness Study), the authors found that three previously used prediction formulas underestimated true max heart rate in people older than 30. They proposed a better fit: max heart rate equals 211 minus 0.64 times age. The relationship showed no interaction with sex, physical activity level, fitness (VO2max), or body-mass index, though individual results still varied by about 11 bpm (standard error 10.8 bpm) around the prediction.
n=3320
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This American Heart Association scientific statement is a consensus guideline, not an experiment. Drawing on more than 600 cited references, it sets standards for exercise testing (treadmill and cycle protocols, ECG monitoring, safety) and for prescribing exercise. It accepts heart rate for setting training intensity but notes that the common 220-minus-age formula varies by about ±12 bpm among people of the same age; a cardiopulmonary exercise test gives the most accurate basis, and heart-rate-reserve targets adjust for individual resting heart rate. It states that exercise training has consistently been shown to be very safe, even in adults with known cardiovascular disease.
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Maximal heart rate was strongly related to age (r = -0.90), best described by 208 - 0.7 x age; the laboratory study gave a nearly identical 209 - 0.7 x age. The relationship did not differ between men and women or with habitual physical activity. The widely used 220 - age formula underestimates maximal heart rate in older adults, which would understate the intensity of prescribed exercise.
n=18712
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Percentage of heart rate reserve matched percentage of VO2 reserve almost exactly, with a mean intercept of -0.1 and slope of 1.00 that were not distinguishable from the line of identity. Against %VO2max the relationship was offset, with a mean intercept of -11.6 and slope of 1.12, both significantly different from 0 and 1 (P < 0.001). The gap between %HRR and %VO2max was larger in less fit subjects (significant inverse relationship with VO2max, P < 0.01). The authors concluded that %HRR is equivalent to %VO2 reserve, not %VO2max, and that this relationship should be used in exercise prescription.
n=63
Why we call confidence high
Two large data sets anchor the age formulas. A meta-analysis of 351 studies and 18,712 adults (Tanaka 2001) found maximum heart rate tracks age closely, and the HUNT study of 3,320 adults (Nes 2013) found age alone is practically convenient but misses any one person by about 11 beats per minute. Both found the older formulas, such as 220 minus age, underestimate maximum heart rate in older adults. The AHA exercise standards (Fletcher 2013) use heart rate to set training intensity. Heart rate reserve (the Karvonen method) tracks percent of oxygen-uptake reserve almost one to one (slope 1.00 in 63 adults, Swain and Leutholtz 1997), but not percent of VO2max, where the gap is larger in less fit people. The honest limit is that individual error, and Liu 2025 shows formula targets only sometimes land on a measured threshold, in adults with metabolic syndrome.
Where it applies
Healthy adults
Last reviewed Oct 14, 2026. See how we score.