Target heart rate (Karvonen)

The formula

• HR_target = (HR_max − HR_rest) · i + HR_rest

HR_max − HR_rest is the heart rate reserve: the beats per minute the heart has to spare between rest and its maximum. i is the intensity as a fraction of that reserve, 0.7 for 70%. The target is the resting rate plus that share of the reserve; the source, Karvonen, Kentala and Mustala (1957), is cited under the formula.

Holds when the maximum is the person’s own. A maximum estimated from age is a population average with a spread of ten beats or more either way, and the target carries that spread with it.

A worked example

Maximum 180, resting 60, intensity 70%: the reserve is 180 − 60 = 120, 120 · 0.7 = 84, and 84 + 60 = 144 beats per minute. At 85% the same person’s target is 120 · 0.85 + 60 = 162.

Why the reserve and not the maximum

The simpler rule, a share of the maximum alone, gives the same target to a trained person with a resting rate of 45 and an untrained one with 75. The reserve method starts each from their own resting rate, so 70% of reserve is a harder effort for the fitter heart, which is the point. The two scales meet at 100% and diverge below it.

Zones

Training plans cut the reserve into zones, 50–60% up to 90–100%, and the heart rate zone calculator lays them out for a given maximum and resting rate. The maximum itself comes from a test or from an age formula on the maximum heart rate page.

Common mistakes

• Using the intensity as a percentage. The formula takes a fraction: 0.7, not 70.
• Measuring the resting rate after coffee or on the way to work. It is taken lying down, on waking.
• Treating the target as a prescription. It is an average for people with those two numbers, and not medical advice; a doctor decides what is safe for a given heart.

Frequently asked questions