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Archived noindex page. Kefiw's public focus is Property decision help.

Archived page

This older Kefiw page is kept for reference, marked noindex, and removed from the primary sitemap. The current Kefiw experience is focused on property decisions: cost, quotes, damage, buying, selling, owning, and packets.

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Operational Heart Rate Zones · Karvonen

Karvonen zones using HR reserve — more accurate than flat %HRmax.

Karvonen factors resting heart rate into zone calculation: zone_bpm = (HRmax − HRrest) × intensity + HRrest. More personalised than flat %HRmax — a fit person's resting HR is lower, so their zones shift up.

Part of: Structural Output

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Fields marked optional can be skipped; results update as you type
Operational Heart Rate Zones · Karvonen
HR Max (220 − age)
185 bpm
Reserve (HRR)
123 bpm
Operational Zones
Z1 · Warm-up124–136 bpmActive recovery, fat oxidation
Z2 · Aerobic136–148 bpmEndurance base, mitochondrial density
Z3 · Tempo148–160 bpmLactate threshold edge
Z4 · Threshold160–173 bpmVO₂max development
Z5 · Redline173–185 bpmAnaerobic · ≤ 2 min sustainable
Karvonen: zone_bpm = (HRmax − HRrest) × intensity% + HRrest. HRmax (220−age) is population estimate; lab test (VO₂max) is more accurate.

How to use

  1. Measure resting HR first thing in the morning (average over 3 days).
  2. Enter age and resting HR.
  3. Read the five zones with BPM ranges and physiological purpose.

Examples

35y · resting 62
HRmax 185 · HRR 123. Z2 aerobic 136–148 · Z4 threshold 160–173.

Before you act on the result

Health-related tools are educational planning aids. They can make a number or assumption visible, but they do not diagnose, treat, prescribe, or replace clinician guidance.

If the result points to risk, symptoms, medication questions, or urgent changes, use it as a note for a qualified professional rather than a final decision.

Next up

Zones set. Now count the calories burned.Kinetic Expenditure · MET → Pushing hard? Check sleep recovers the system.REM-Sync · Sleep Cycles →

Frequently asked questions

› Is 220 − age accurate? Trust & accuracy

Population estimate with ±10 bpm standard deviation. Lab test (VO₂max or field test) is more accurate.

› Which zone burns the most fat?

Z2 burns highest % fat; Z3-4 burn more total calories (and still substantial fat grams). Pure "fat-burning zone" framing misleads.

Tips & related reading

See the Structural Output hub →

Tips & how-tos

Relevant links

Related tools

Kinetic Expenditure · MET

Calories burned per activity using the MET (Metabolic Equivalent of Task) method from the Compendium of Physical Activities.

Max Load Capacity · Brzycki 1RM

Estimate one-rep maximum from a sub-max set using the Brzycki formula. Recovery / Hypertrophy / Strength zones.

REM-Sync · Sleep Cycles

Find the optimal bedtime or wake time based on 90-minute sleep cycles. Wake at the end of a cycle, not the middle.