Heart Rate Reserve: Better Zones with the Karvonen Method
Heart rate reserve (HRR) is the gap between your maximum and resting heart rates. It's the working range your heart actually has available for exercise. If your max is 190 and you rest at 50, your reserve is 140 beats. The Karvonen method turns that reserve into training zones: instead of taking a flat percentage of your maximum, it takes a percentage of your reserve and adds your resting heart rate back on top. That one adjustment makes your zones noticeably more personal, especially if you're very fit or just starting out. Here's how it works and how to use it.
What is heart rate reserve?
Your heart rate never drops to zero, so not all of your "190 bpm" is usable training range. Heart rate reserve is the part that is:
HRR = maximum heart rate − resting heart rate
It represents the beats you have to spend between sitting still and going all-out. A fitter heart pumps more blood per beat, so it beats slower at rest. That means a fitter person has a larger reserve than an unfit person with the same maximum. That difference is exactly what plain percent-of-max ignores and what heart rate reserve captures.
The Karvonen formula
The Karvonen method, published by Finnish physiologist Martti Karvonen in 1957, sets each zone boundary like this:
Target HR = resting HR + (intensity % × heart rate reserve)
Say your max is 190, your resting heart rate is 50, and you want the bottom of your Zone 2 at 60% intensity:
- Heart rate reserve = 190 − 50 = 140 bpm
- 60% of 140 = 84 bpm
- Add resting back: 84 + 50 = 134 bpm
So your 60% Karvonen target is 134 bpm. Note that a naive "60% of max" would have given you 114 bpm, a full 20 beats lower. That gap is the whole point: the two methods are not measuring the same thing.
Heart-rate reserve
135bpm
185 − 50
Max heart rate
185bpm
Resting heart rate
50bpm
| Zone | Range | What it trains |
|---|---|---|
| Z1 | Recovery 118–131 bpm | Active recovery and warm-up; promotes blood flow without adding fatigue. Very easy, RPE 1–2. Full conversation, barely breathing hard. |
| Z2 | Endurance 131–145 bpm | Aerobic base, fat oxidation and capillary density, the bread-and-butter zone. Comfortable, RPE 3–4. Can hold full sentences. |
| Z3 | Tempo 145–158 bpm | Aerobic capacity and muscular endurance; 'moderately hard' steady work. Working, RPE 5–6. Short sentences only. |
| Z4 | Threshold 158–172 bpm | Lactate threshold, your sustainable race-pace ceiling. Hard, RPE 7–8. A few words at a time. |
| Z5 | VO₂max 172–185 bpm | Maximal aerobic power and VO₂max via short, hard intervals. Very hard to maximal, RPE 9–10. No talking. |
Z1 · Recovery. Active recovery and warm-up; promotes blood flow without adding fatigue. Very easy, RPE 1–2. Full conversation, barely breathing hard.
Z2 · Endurance. Aerobic base, fat oxidation and capillary density, the bread-and-butter zone. Comfortable, RPE 3–4. Can hold full sentences.
Z3 · Tempo. Aerobic capacity and muscular endurance; 'moderately hard' steady work. Working, RPE 5–6. Short sentences only.
Z4 · Threshold. Lactate threshold, your sustainable race-pace ceiling. Hard, RPE 7–8. A few words at a time.
Z5 · VO₂max. Maximal aerobic power and VO₂max via short, hard intervals. Very hard to maximal, RPE 9–10. No talking.
- Karvonen anchors zones to your heart-rate reserve (HRmax − resting HR), so it personalizes zones to your fitness better than plain %HRmax, a fit athlete with a low resting HR gets correspondingly lower targets.
- Measure resting heart rate first thing in the morning, lying down, before caffeine. A 5-bpm error in RHR shifts every zone.
A PDF of your personalized results, with a QR code to reopen them anytime.
Why does Karvonen beat plain %HRmax?
Percent-of-maximum zones treat everyone with the same max identically, no matter their fitness. Karvonen doesn't, because resting heart rate is a rough proxy for fitness, and folding it in shifts your zones to fit you:
- It accounts for your conditioning. A trained athlete resting at 45 and an unfit beginner resting at 75, even with the same max, get different and more appropriate zones, because the reserve they're working within is genuinely different.
- The zones track your fitness over time. As you get fitter and your resting heart rate drops, your reserve grows and your zones update with it. A fixed %HRmax band never moves.
- It spreads the easy end out. Plain %HRmax tends to put easy efforts at implausibly low, hard-to-hold heart rates; adding resting heart rate back lifts the low zones to numbers you can actually train at.
It is not magic. It still leans on two numbers you have to measure. But for a heart-rate method it's a clear step up from a flat percentage. For how the different systems carve up the range, compare the heart-rate zone models.
How do I find the two numbers I need?
Karvonen is only as good as your max and resting heart rates, so get both honestly.
Resting heart rate (RHR). Measure it first thing in the morning, before you get up, ideally averaged over several days. A chest strap or the overnight reading from a wearable both work. Don't use a daytime "sitting at my desk" number, since it runs high.
Maximum heart rate (HRmax). The age formulas (like 220 − age, or the more accurate Tanaka, 208 − 0.7 × age) are convenient but can be off by 10+ beats for any individual. A proper field test gives a far better number. Our guide on finding your maximum heart rate walks through both the estimates and a real test, and the max heart rate calculator gives you the estimate in one step.
Because a 10-beat error in either input shifts every Karvonen zone, it's worth measuring rather than guessing, especially your max.
Karvonen vs. lactate-threshold zones
Karvonen is a big improvement over %HRmax, but it's still anchored to your maximum, which barely responds to training and is hard to measure safely. The most individualized heart-rate anchor is your threshold, not your max. If you can test it, anchoring zones to your lactate-threshold heart rate puts the boundaries where your physiology actually changes, and they rise as you get fitter. Many athletes use Karvonen as an accessible starting point and graduate to threshold-based LTHR zones once they've done a 30-minute test.
For setting your easy aerobic work specifically, pair this with the talk test rather than trusting the number alone. See Zone 2 heart rate, explained.
Sources
Karvonen, M. J., Kentala, E., & Mustala, O. (1957), the original study introducing the heart-rate-reserve method. Maximum-heart-rate estimation follows Tanaka, Monahan & Seals (2001).