Heart-Rate Reserve (Karvonen Method)

Heart-rate reserve (HRR) is the difference between maximal heart rate and resting heart rate:

HRR = HRmax − HRrest

The Karvonen formula computes a target heart rate for a chosen intensity percentage:

Target HR = (HRR × %intensity) + HRrest = [(HRmax − HRrest) × %intensity] + HRrest

HRmax is commonly estimated as 220 − age (see hrmax-calculation), and HRrest is measured (ideally on waking; see resting-heart-rate).

The advantage over a plain percentage of HRmax (see percent-hrmax) is individualization: by anchoring to the person's own resting heart rate, the Karvonen method gives a higher, fitter-adjusted target for someone with a low resting HR. The %HRR scale also lines up closely with %VO2 reserve (see vo2-reserve), which is why ACSM expresses intensity in both. For reference, ACSM classifies 40–59% HRR as moderate intensity and ≥60% HRR as vigorous (see intensity-classification).

Worked example: a 40-year-old with HRrest 60 bpm. HRmax ≈ 220 − 40 = 180; HRR = 180 − 60 = 120. A 60% target = (120 × 0.60) + 60 = 132 bpm.

• HRR = HRmax − HRrest.
• Karvonen target HR = (HRR × %intensity) + HRrest.
• HRmax often estimated as 220 − age; HRrest measured at rest.
• More individualized than %HRmax because it accounts for resting HR.
• %HRR ≈ %VO2 reserve; ACSM moderate = 40–59% HRR, vigorous = ≥60% HRR.

• percent-hrmax — the simpler alternative this improves on.
• vo2-reserve — the metric %HRR closely matches.
• heart-rate-zones — zones can be built on %HRR.
• intensity-classification — the %HRR moderate/vigorous cutoffs.
• hrmax-calculation — supplies HRmax for the formula.