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The Two Methods

Karvonen (heart rate reserve). Subtract resting HR from max HR. That's your "reserve" — the range your heart actually operates in. Zones are set as percentages of that reserve, added back to resting HR. It's the most common method because it only needs two numbers a watch can give you.

Target HR = resting_HR + (max_HR - resting_HR) × intensity_fraction

Joe Friel LTHR. Lactate threshold heart rate is the highest HR you can sustain for 30-60 minutes at steady effort. Zones are set as percentages of LTHR. It's more accurate than Karvonen for trained runners because LTHR is anchored to a real metabolic event, not an estimated maximum. The downside: you have to do a 30-minute time trial to find LTHR.

Why Five Zones?

The five-zone model maps to distinct physiological adaptations:

  • Zone 1 — Recovery. Below the aerobic threshold. Pure parasympathetic-recovery work. Easy enough to hold a conversation in full sentences.
  • Zone 2 — Aerobic / Easy. Mitochondrial density and fat oxidation. Where 70-80% of total training volume should live for most runners.
  • Zone 3 — Tempo / Marathon. Just below the lactate threshold. Marathon goal pace lives here for most runners.
  • Zone 4 — Threshold. The lactate-clearance pace. Tempo runs and threshold intervals target this zone.
  • Zone 5 — VO2max. Maximal aerobic capacity. Short intervals (3-6 min) at very hard effort.

Common Mistakes

  1. Using 220 - age for max HR. This formula is off by ±10-15 bpm for most adults. Use the Tanaka formula (208 - 0.7 × age) as a better estimate, but ideally test it.
  2. Letting HR drift control easy runs. Heart rate drifts up 5-10 bpm during a long run at constant pace (cardiac drift). Don't slow down to chase a number — let the early miles set the pace.
  3. Treating heart rate as primary on hills or in heat. HR responds to many things — caffeine, dehydration, sleep deprivation, ambient temperature. Use pace as the primary control on most days.
  4. Skipping the LTHR test. If you train seriously, the 20-30 minutes once a quarter is worth it. Karvonen with a wrong max HR can put your zones off by 10+ bpm.

For pace-based equivalents, run a recent race time through the VDOT calculator. For the bigger picture on intensity distribution, see the polarized running training article.