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Category Sport & Fitness

Age (years) 10–100 years

Resting HR (bpm) 30–120 bpm

Max HR (bpm, optional) If blank, Tanaka formula used

AT Intensity (%)

85%

Typical AT: 80–90% HRR

HRmax Formula

Anaerobic Threshold Heart Rate — bpm

Training Zones

Zone	Name	HR Range	% HRmax

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About

The anaerobic threshold (AT) marks the exercise intensity at which lactate accumulates in blood faster than it can be cleared. Below this point, aerobic metabolism dominates. Above it, glycolytic pathways flood the system with lactate, limiting performance to minutes rather than hours. Misidentifying your AT by even 5 bpm shifts your entire training plan: too low and you stagnate; too high and you accumulate fatigue without adaptation. Laboratory gas-exchange testing (measuring VCO₂/VO₂ crossover) remains the gold standard, but field-based estimation using heart rate reserve or deflection-point analysis provides actionable accuracy for most athletes.

This calculator implements three estimation methods. The Karvonen method uses heart rate reserve (HRR = HR_max − HR_rest) and places AT at a configurable intensity fraction, typically 0.80 - 0.90. The %HRmax method applies a direct percentage to maximum heart rate. Age-predicted HR_max follows the Tanaka equation (208 − 0.7 × Age), which outperforms the older Fox formula across populations. Note: all field estimates assume a healthy cardiovascular system and carry ±5 - 10 bpm uncertainty. Medications such as beta-blockers invalidate heart rate-based predictions entirely.

Formulas

The Karvonen method computes target heart rate from heart rate reserve (HRR), defined as the difference between maximal and resting heart rate. The anaerobic threshold intensity fraction f typically falls between 0.80 and 0.90 for trained athletes.

HR_AT = HR_rest + f × (HR_max − HR_rest)

Where HR_AT = heart rate at anaerobic threshold bpm, HR_rest = resting heart rate bpm, HR_max = maximum heart rate bpm, and f = intensity fraction (dimensionless, 0 - 1).

When maximum heart rate is unknown, the Tanaka age-predicted formula provides an estimate with standard deviation of ±10 bpm:

HR_max = 208 − 0.7 × Age

The direct %HRmax method bypasses resting heart rate entirely:

HR_AT = HR_max × p

Where p = percentage of max heart rate (typically 0.85 - 0.92). Training zones are then derived by dividing the range from HR_rest to HR_max into five bands anchored around the computed HR_AT.

Reference Data

Zone	Name	% HRmax	% HRR (Karvonen)	Typical RPE	Duration Sustainable	Primary Energy System	Training Purpose
1	Recovery	50 - 60%	40 - 50%	1 - 2	> 3 hr	Aerobic (fat oxidation)	Active recovery, warm-up
2	Aerobic Base	60 - 70%	50 - 65%	3 - 4	1 - 3 hr	Aerobic (mixed fat/carb)	Endurance building, fat metabolism
3	Tempo	70 - 80%	65 - 80%	5 - 6	30 - 90 min	Aerobic (carb dominant)	Aerobic capacity, marathon pace
4	Threshold (AT)	80 - 90%	80 - 90%	7 - 8	10 - 40 min	Mixed aerobic/anaerobic	Lactate clearance, race pace
5	VO₂max / Anaerobic	90 - 100%	90 - 100%	9 - 10	1 - 8 min	Anaerobic glycolysis	Max power, sprint capacity
Common HRmax Prediction Formulas
-	Tanaka et al. (2001)	HR_max = 208 − 0.7 × Age (SD ±10 bpm)
-	Fox (1971, legacy)	HR_max = 220 − Age (SD ±12 bpm)
-	Gulati (Women, 2010)	HR_max = 206 − 0.88 × Age
-	Gellish (2007)	HR_max = 207 − 0.7 × Age
Lactate Reference Values
-	Resting blood lactate	0.5 - 1.5 mmol/L
-	Aerobic threshold (LT1)	≈ 2.0 mmol/L
-	Anaerobic threshold (LT2/OBLA)	≈ 4.0 mmol/L
-	Maximal effort lactate	8 - 25 mmol/L
Typical AT as % HRmax by Sport
-	Elite marathon runner	88 - 92% HRmax
-	Trained cyclist	85 - 90% HRmax
-	Recreational runner	80 - 85% HRmax
-	Untrained individual	75 - 80% HRmax
-	Elite swimmer	82 - 88% HRmax
-	Cross-country skier	86 - 92% HRmax

Frequently Asked Questions

The Karvonen method uses heart rate reserve (HRR = HR_max − HR_rest), which accounts for individual cardiac fitness. A person with HR_rest of 50 bpm and another at 75 bpm will get different target zones even with identical HR_max. The %HRmax method ignores resting heart rate entirely, making it simpler but less individualized. For well-trained athletes with low resting rates, Karvonen produces more accurate threshold estimates.

The Fox formula (220 − Age) was derived from limited data in 1971 and overestimates HRmax in younger populations while underestimating it in older adults. Tanaka et al. (2001) performed a meta-analysis of 351 studies totaling 18,712 subjects and found 208 − 0.7 × Age to be more accurate across all age groups, with a lower standard deviation (±10 vs ±12 bpm).

Yes. Beta-blockers (metoprolol, atenolol) directly suppress heart rate by 20 - 30 bpm, invalidating all percentage-based calculations. Calcium channel blockers (diltiazem, verapamil) also reduce HR. Stimulants and caffeine can elevate resting HR. If you take any chronotropic medication, heart rate-based threshold estimation is unreliable. Use Rate of Perceived Exertion (RPE) or lab-based lactate testing instead.

The terms are often used interchangeably but refer to distinct physiological events. The first lactate threshold (LT1) occurs around 2.0 mmol/L blood lactate, where production begins to exceed resting clearance. The second threshold (LT2), also called Onset of Blood Lactate Accumulation (OBLA), occurs at approximately 4.0 mmol/L. The ventilatory anaerobic threshold (VAT) closely tracks LT2 in most individuals. This calculator estimates the LT2/OBLA equivalent using heart rate.

The polarized training model, supported by research on elite endurance athletes, prescribes approximately 80% of training volume in Zones 1-2 (below AT) and 20% in Zones 4-5 (at or above AT). Zone 3 (tempo) is used sparingly as it generates significant fatigue without the stimulus of higher-intensity work. A typical week for a runner might include 3 - 4 easy runs in Zone 2, 1 threshold session at Zone 4 for 20 - 40 min, and 1 interval session touching Zone 5.

At elevations above 1500 m, reduced partial pressure of oxygen (pO₂) shifts the threshold to a lower absolute heart rate. The reduction is approximately 1 - 2 bpm per 300 m of elevation gain above 1500 m. Acclimatization over 2 - 3 weeks partially restores threshold HR. When training at altitude, subtract 3 - 8 bpm from sea-level zones as a practical adjustment.