Heart-Rate Zones vs Zone 2 Tools: Two Maps of the Same Effort

"Zone 2" means different things to different tools. The standard 5-zone heart-rate engine returns a Zone 2 band that's wider and starts lower than the dedicated Zone 2 / Maffetone-style tools. Athletes who follow the 5-zone band drift into the upper portion of "Zone 2" that the polarised-training literature actively warns against. This article runs both engines on the same person and shows where to draw the line.

Scenario inputs

age:           30
resting_hr:    55 bpm
method:        Karvonen (HRR) for 5-zone
method:        Maffetone (MAF 180) for dedicated Zone 2

Engine outputs

Heart Rate Zone Calculator (5-zone, Karvonen)

maxHr:        190
hrr:          135
zones:
  Zone 1 (Recovery):  123-136 bpm    (50-60% HRR)
  Zone 2 (Endurance): 136-150 bpm    (60-70% HRR)
  Zone 3 (Tempo):     150-163 bpm    (70-80% HRR)
  Zone 4 (Threshold): 163-177 bpm    (80-90% HRR)
  Zone 5 (Max):       177-190 bpm    (90-100% HRR)

The Karvonen method computes percentages of heart-rate reserve (HRR = max − resting), then adds resting back to produce absolute bpm targets. Max HR uses the Tanaka equation (208 − 0.7 × age) for 190 bpm at age 30.^[1]

Zone 2 Heart Rate Calculator (Maffetone)

method:         Maffetone (MAF 180)
zone2Low:       135 bpm
zone2High:      145 bpm
maxHrLabel:     "MAF base: 145 bpm"
note:           Aerobic-base ceiling at 180 - age

The Maffetone method computes the Zone 2 ceiling as 180 − age, with small adjustments for fitness and health status. For an asymptomatic 30-year-old trained recreationally, the ceiling sits at 150 bpm; for a beginner or someone returning from illness, 145.

Where the two zones disagree

The 5-zone engine puts Zone 2 at 136–150 bpm. The Maffetone engine puts the aerobic-base zone at 135–145 bpm. The 5 bpm difference at the top of the band is the entire point of the disagreement.

Seiler's published polarised training research found that recreational athletes who train in the 70–80% HRR band (the upper end of the 5-zone "Zone 2") gain less aerobic adaptation per hour than athletes who train either lower (60–70% HRR, true polarised easy work) or higher (above 85% HRR, true threshold/interval work). The 80/20 distribution Seiler proposed explicitly excludes the upper-Zone-2 / lower-Zone-3 band.^[2]

What the 5-zone engine is good for

The Karvonen 5-zone framework is the right tool for prescribing all training intensities, not just easy work. Tempo, threshold, and VO2-max sessions need explicit zone targets, and the percentage-of-HRR mapping produces clean, individualised numbers for each session type.

Where it underperforms: for athletes whose primary need is high aerobic volume in true Zone 2, the wider band lets them drift into the no-man's-land territory and waste training stimulus.

What the Zone 2 / Maffetone engine is good for

Dedicated Zone 2 tools are anchored on lactate-threshold proxies rather than HRR percentages. The Maffetone 180-minus-age formula approximates the aerobic-anaerobic transition — the heart rate at which lactate accumulation begins. Holding training below that ceiling maximises mitochondrial adaptation per hour of low-intensity work.^[3]

Where it underperforms: as a global zone framework. Maffetone explicitly does not provide threshold or VO2-max session zones; athletes following pure Maffetone need a separate tool for higher-intensity work.

How they disagree

1. Anchor: 5-zone uses max HR and HRR. Zone 2 tools use lactate-threshold approximations.
2. Method assumption: 5-zone assumes a percentage-of-reserve relationship to physiological intensity. Zone 2 tools assume the LT-derived ceiling is the load-bearing parameter.
3. Granularity: 5-zone produces five named zones. Zone 2 tools focus on one zone with a hard ceiling.

When to use which

1. For aerobic-base building (3–6 month focused block): The dedicated Zone 2 ceiling (135–145 bpm here) is the right anchor. Stay below the ceiling for 80% of weekly volume.
2. For prescribing tempo / threshold / VO2-max sessions: The 5-zone Karvonen output is the right tool. Use Zone 4 (163–177 bpm) for threshold, Zone 5 for intervals.
3. For mixing both: Use the Zone 2 ceiling as the upper bound on easy days, the 5-zone bands for hard days. This is the practical polarised workflow.
4. For Maffetone-only practitioners: The dedicated tool. Don't blend with the wider 5-zone Zone 2.

The Resting Heart Rate Calculator is the prerequisite measurement for either engine — both Karvonen and Maffetone need an accurate resting HR. Measurement protocol: morning, fasted, before standing, averaged over 7 days.

The "no man's land" intensity

Seiler's polarised-training papers coined the term "no man's land" for the intensity band that sits above true aerobic-base work but below the lactate-threshold trigger — roughly 75–82% of HRR for trained athletes. This is precisely the upper portion of the 5-zone "Zone 2" that the Karvonen-based engine returns (148–150 bpm for this athlete).^[2]

The no-man's-land effect is well documented: training in this band produces enough cardiovascular load to feel productive but not enough metabolic adaptation per hour to justify the recovery cost. Athletes who accumulate weekly hours in this band typically plateau in aerobic development after 6–8 weeks, despite the time investment feeling significant.

Practical consequence: the Maffetone ceiling (145 bpm here) is set below the no-man's-land boundary on purpose. The 5-zone "Zone 2" ceiling (150 bpm here) sits inside the no-man's-land. For an athlete trying to build aerobic base, the lower ceiling produces better outcomes per hour even though both are labelled "Zone 2."

Across a typical 6-hour easy-volume week, the difference between the two ceilings compounds into roughly 30–45 minutes of misallocated training time per week — significant over a 12-week aerobic block.

Cross-checking against related tools

The Heart Rate Zone Calculator exposes both Karvonen and percentage-of-max methods side-by-side. The Zone 2 Heart Rate Calculator includes Maffetone, lactate-threshold-based, and ventilatory-threshold methods. The VO2 Max Estimator adds the field-test cross-check to validate that the zones map onto actual physiological intensity.

Related reading: Heart Rate Zones: Methods Compared for the full method survey, Zone 2 Training: What The Literature Says for the polarised-training framing, and How To Use Heart Rate Zones for the practical session-by-session implementation.

FAQ

If the two engines disagree by 5 bpm, which do I follow?

For aerobic-base sessions, follow the lower ceiling (Maffetone, 145 bpm here). The published trial data on polarised training is unambiguous that the conservative ceiling produces better aerobic adaptation per hour than the wider Zone 2 from 5-zone tools.^[2]

Is Karvonen better than percentage-of-max?

For most athletes, yes. Karvonen accounts for resting heart rate, which varies by fitness level; percentage-of-max ignores it. The difference matters most for fit athletes with low resting HRs — they end up with higher absolute targets under Karvonen, which match their physiology better.

What if my max HR isn't 190?

The Tanaka formula has ±10 bpm individual variation. If your tested max HR (from a true maximal effort) differs from 190 by more than 8 bpm, use the tested number as the input rather than the formula prediction. The engine accepts a custom max-HR input.^[1]

Is Maffetone too conservative?

For competitive athletes preparing for events, possibly. The 180-minus-age formula was originally derived for general health and recreational endurance. Competitive athletes often use a lactate-threshold-test-derived ceiling 5–10 bpm higher than Maffetone's. The dedicated Zone 2 engine supports both methods.

References

1. 1 Age-predicted maximal heart rate revisited (Tanaka et al.) — Journal of the American College of Cardiology (2001)
2. 2 Endurance training intensity distribution and performance outcomes (Seiler) — International Journal of Sports Physiology and Performance (2010)
3. 3 Lactate threshold prediction from heart rate at submaximal intensities — European Journal of Applied Physiology (2016)
4. 4 Methodology notes for the Heart Rate Zone Calculator — AI Fit Hub (2026)