Key Takeaways

  • "Anaerobic threshold" is not one number. It is used for lactate thresholds, ventilatory thresholds and other markers, and reviews find they can differ[9][10][11]. This tool gives a heart rate at the second threshold and says which marker each answer is closest to.
  • The usual free method is a hard solo field test. Joe Friel's 30-minute version uses the average of the last 20 minutes[1], and the 20-minute version in his guide revised in September 2025 uses the average minus 5%[2].
  • Against lab thresholds the 30-minute test had a standard error of 5.7 to 8 bpm in runners[3][4], and ran about 6 to 6.8 bpm high in cyclists[5]. Good for training, not for precision.
  • With no test, a flat percent of maximum is a poor guide. In 1,272 lab-tested people, the second ventilatory threshold averaged 90.6 to 95.6% of measured maximum, and rose with training status[6].
  • There is no zone table here. Friel's current table is an image I could not read, and his older one has been replaced by him. See the Zone 2 and Target Heart Rate tools for zones.

What the Anaerobic Threshold Is, and Why It Has So Many Names

Everyone means roughly the same idea, but the number depends on how it was measured.

The idea is a point in a hard effort where the body stops holding a steady state and fatigue starts to build quickly. Scientists have named it many ways: lactate threshold, ventilatory anaerobic threshold, onset of blood lactate accumulation, heart rate deflection point and maximal lactate steady state[11].

They are not interchangeable. A 1988 review concluded the lactate threshold and the ventilatory threshold are not produced by the same mechanism, and sometimes one comes first and sometimes the other[10]. A 2009 review counted 25 different lactate threshold concepts[9].

Some labs fix it at a blood lactate of 4 mmol/L. In 18 men, the running speed at that point explained 92% of the variation in marathon speed[13]. Others find the point on the lactate curve farthest from the line joining its two ends, called D-max[14].

A newer argument is that the real boundary is critical power, not the maximal lactate steady state, which Jones and colleagues say underestimates the highest steady metabolic rate[12].

Joe Friel calls the heart rate from his field test the lactate threshold heart rate, and notes it is also often called the anaerobic threshold or functional threshold heart rate[1]. This page uses it that way, as a training anchor and not a diagnosis.

How the Calculator Works

Three starting points. Pick the one that matches what you have.

A field test. You do a hard solo effort and enter an average heart rate. For the 30-minute test the result is that average for the last 20 minutes, with no change[1]. For the 20-minute test the result is the average for all 20 minutes, minus 5%[2].

Worked examples: field tests

30-minute test: a last-20-minute average of 165 bpm gives a threshold of 165 bpm. The tool shows 157 to 173 bpm as one standard error either side. With a maximum of 185, that is 89.2% of maximum. 20-minute test: an average of 170 bpm minus 5% is 170 × 0.95 = 161.5, which rounds up to 162 bpm.

A result you already have. If a lab, a ramp test or your watch has given you a threshold heart rate, enter it. The tool shows it as a percent of your maximum and of your heart rate reserve, and sets it beside the lab averages below. The reserve figure is arithmetic: (threshold − resting) ÷ (maximum − resting).

No test. The tool applies lab averages for your sex and training status to your maximum heart rate, with one standard deviation either side. It is a range, not a point, because the lab data are a spread of people.

Worked example: no test

A man with a measured maximum of 182 bpm, medium training status. The lab average for that group is 93.5% at the second threshold, so 93.5% × 182 = 170 bpm. One standard deviation (3.4 points) either side gives 164 to 176 bpm. The printed table for that group gives 170 bpm at the second threshold at an average maximum of 182, which matches.

Your maximum heart rate comes from a number you measured, or from the same six age equations as the Target Heart Rate Zones calculator. Halves round up.

How to Do the Field Test

Friel's rules, and what the studies found when they checked them.

  1. Warm up the way you normally would. Friel's guides do not give a warm-up routine. For the power version of the test he says a road that is flat or a steady slight climb, with no stop signs or heavy traffic, gives better results[2].
  2. Test in the sport you want the number for. His current guide drops separate running and cycling ranges and relies on test data from the sport itself[2].
  3. Go alone. Friel says doing it in a race or with training partners pushes the number too high[1].
  4. Pace it as steady race effort, for the full time. Friel warns that most people start too fast and fade, which gives inaccurate data[1][2]. For the 20-minute test he suggests starting conservatively and deciding every 5 minutes whether to go a little faster[2].
  5. Do not watch your heart rate during the test. You are not aiming for a number[1].
  6. For the 30-minute test, press lap at 10 minutes and read the average for the last 20. For the 20-minute test, read the average for the whole effort and subtract 5%[1][2].
  7. Repeat it. Friel suggests early in base and build periods and about every six weeks, since the number changes with fitness[2].

Friel has given two versions. His 2011 post uses 30 minutes with the last 20 averaged[1]. His guide revised in September 2025 uses 20 minutes with 5% off[2].

A TrainingPeaks reprint of his older guide, updated July 2026, still shows the 30-minute test[26]. I found no study comparing the two, so pick one and repeat that one.

StudyWhoCompared withResult
Kraus 2011 (abstract)[3]20 runnersVentilatory threshold HRr = 0.69, SEE 5.7 bpm
McGehee 2005[4]27 runners and triathletesHR at 4 mmol/L lactateNo difference, SEE 8 bpm
Partridge 2016 (abstract)[5]50 cyclists and triathletesLT HR (1.5 mmol/L, D-max)Overestimated by 6.8 and 6 bpm

Studies that compared a field test with a lab threshold

That is why the 30-minute result comes with a range of ±8 bpm, the larger of the two running errors. The cycling authors concluded the test should not be used when precision is needed[5].

Two of the three are conference abstracts, and I could not read any of the full texts. McGehee's abstract does not say which part of the 30 minutes was averaged. I found no independent study of the 20-minute minus 5% rule, so the tool gives no range for it.

The Conconi test, which looks for a bend in heart rate against speed, is not offered. A review found its validity uncertain, although deflection points relate closely to the second lactate turn point when they can be found[15].

Where the Second Threshold Sits in Lab Data

1,272 people on a treadmill, with gas exchange measured.

Benítez-Muñoz and colleagues tested 971 men and 301 women with a ramp treadmill test to exhaustion and found both ventilatory thresholds[6]. They sorted people into low, medium and high training status from their oxygen uptake at the two thresholds and at VO2max.

The men averaged 36.8 years old, and the women 33.9. They were volunteers who came to a Spanish university lab for an exercise test between 2003 and 2023, not a random sample.

GroupPeopleVT1 % of maxVT2 % of maxVT2 bpmMax bpm
Men, low21274.6 ± 6.590.6 ± 5.2162 ± 13179 ± 11
Men, medium43678.6 ± 5.493.5 ± 3.4170 ± 10182 ± 10
Men, high31780.8 ± 4.894.6 ± 2.6175 ± 10185 ± 10
Women, low5377.9 ± 7.193.1 ± 4.1164 ± 13177 ± 12
Women, medium16081 ± 5.294.6 ± 3.2169 ± 12179 ± 12
Women, high8082.9 ± 4.995.6 ± 2.6176 ± 12184 ± 13

Mean percent of measured maximum heart rate at each ventilatory threshold, plus or minus one standard deviation (Table 2 of the paper)

Three things stand out.

  • The averages rose with training status in both sexes. The paper reports the differences as significant for men across all three groups, and for women between the low group and the other two[6].
  • The averages were also higher for women than for men in every status group, although I did not see the paper test that difference.
  • They are percentages of a measured maximum, not an age equation. The authors say a fixed percent of maximum may not match intensity across people of different training status[6].

Other work points the same way. In 50 experienced cyclists, a fixed percent of maximum misplaced individuals at the first threshold[8].

A Finnish study of 165 recreational runners (64 women) built intensity anchors from sex-specific averages, much as the "no test" mode does. The first lactate threshold came at a higher relative heart rate in women[7].

For the second lactate threshold, the mean error in heart rate was 2.8 to 5.2 bpm. The authors report that errors grew when the maximum values had to be estimated[7].

Some calculators, including the earlier version of this page, apply a flat percentage such as 85%, or 75 to 88% by fitness tier, with no source. The lab means above sit higher, at 90.6 to 95.6%.

The two are not strictly comparable, because the lab figure is a ventilatory marker on a treadmill and is a percent of measured maximum. But a flat figure with no source and no spread is the thing to be wary of.

How Far to Trust the Number

Four reasons a threshold heart rate is a guide, not a fact.

First, the marker. A field test, a lab lactate point and a ventilatory threshold are different things[9][10]. The tool names the marker for each answer.

Second, the test. A poorly paced effort gives the wrong average. Go out too hard and fade, or hold back and never reach threshold, and the number is just a heart rate you held for a while[1][2].

Third, the maximum. If you use an age equation, its error adds to the estimate. Robergs and Landwehr put it at 7 to 11 bpm[16], and Friel warns that 220 minus age is as likely to be wrong as right[2].

Fourth, who was studied. The people in the lab study averaged in their mid-30s, were volunteers, and included fewer women than men[6]. The field-test studies were of runners or of cyclists and triathletes, and the cycling result ran high[5].

Medication and health

Beta blockers slow the heart rate, so you may never reach a standard target however hard you work[24]. The American Heart Association says some medicines lower maximum heart rate[25]. A 20 or 30 minute all-out effort is vigorous. If you have heart disease, chest discomfort or dizziness on exercise, ask a doctor first.

Aerobic Threshold or Anaerobic Threshold?

Two different points on the same scale.

In Friel's current guide, the first lactate threshold (LT1) is the point at 2 mmol/L and tops zone 2, and the second (LT2) is at the border of zones 3 and 4[2]. The aerobic threshold people search for is the first one. The anaerobic threshold is the second.

In the lab data above, the first ventilatory threshold averaged 74.6 to 82.9% of maximum, well under the second. This tool shows that first threshold as a range in the "no test" mode.

For a full zone 2 answer, with the expert panel's definition, Maffetone's formula and the talk test, use the Zone 2 Heart Rate Calculator.

Why There Is No Zone Table Here

Zones built on a threshold need a source, and I could not use the usual ones.

The usual approach is zones as percentages of threshold heart rate. The best-known set is Friel's. His guide revised in September 2025 says he reworked his original 1987 zones, and that running and cycling are no longer split into different ranges[2].

The new table is published as an image, and I could not read the percentages from it. The older table is still widely copied, but he has replaced it, so I left it out.

The earlier version of this page also showed five bands running from 0 to 120% of threshold. Those had no source, and the top band could pass your maximum heart rate, so they are gone.

For zones, use the Target Heart Rate Zones calculator (percent of maximum or of reserve), or the Cycling Power Training Zones calculator if you have a power meter. To see a threshold in a session score, try the TSS calculator.

Limits and What Is Left Out

What the tool does not do, so you do not read more into it than is there.

It gives heart rate only. It does not give a threshold pace or power, because I found no source to turn a heart rate into either. It has no lactate-curve mode, so it cannot work out D-max or a 4 mmol/L point from your blood tests. It does not detect a Conconi deflection point.

It also does not adjust for heat, altitude, sleep, caffeine, or whether you are on a bike or running, and the lab averages are not split by sport.

Your entries are saved in your browser so the page remembers them, and Reset clears them. The calculator does not send them to our server. Ad scripts on the page work separately from it.

Frequently Asked Questions

Sources & References

  1. Determining your LTHR. Friel J. joefrieltraining.com (blog post, April 2011)
  2. A Quick Guide to Setting Zones. Friel J. joefrieltraining.com (revised September 2025)
  3. The 30-minute Time Trial As A Predictor Of Ventilatory Threshold Running Velocity And Heart Rate. Kraus RM, Westerkamp CW, Brtis TK. Medicine & Science in Sports & Exercise 43(5):627 (abstract) (2011)
  4. A comparison of methods for estimating the lactate threshold. McGehee JC, Tanner CJ, Houmard JA. Journal of Strength and Conditioning Research 19(3):553-558 (2005)
  5. Field Test for Estimation of Lactate Threshold Heart Rate. Partridge SM, Seipel AJ, Penry JT. Medicine & Science in Sports & Exercise 48(5S):704 (abstract) (2016)
  6. Differences in the ventilatory thresholds in treadmill according to training status in 971 males and 301 females: a cross-sectional study. Benítez-Muñoz JA, Benito PJ, Guisado-Cuadrado I, Cupeiro R, Peinado AB. European Journal of Applied Physiology 125:499-510 (2025)
  7. The accuracy of fixed intensity anchors to estimate lactate thresholds in recreational runners. Nuuttila O-P, Kaikkonen P, Sievänen H, Vasankari T, Kyröläinen H. European Journal of Applied Physiology 125(8):2161-2171 (2025)
  8. Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries. Meixner B, Filipas L, Holmberg H-C, Sperlich B. Translational Sports Medicine 2025:2008291 (2025)
  9. Lactate threshold concepts: how valid are they?. Faude O, Kindermann W, Meyer T. Sports Medicine 39(6):469-490 (2009)
  10. Possible mechanisms of the anaerobic threshold. A review. Walsh ML, Banister EW. Sports Medicine 5(5):269-302 (1988)
  11. Anaerobic threshold: its concept and role in endurance sport. Ghosh AK. Malaysian Journal of Medical Sciences 11(1):24-36 (2004)
  12. The maximal metabolic steady state: redefining the 'gold standard'. Jones AM, Burnley M, Black MI, Poole DC, Vanhatalo A. Physiological Reports 7(10):e14098 (2019)
  13. Onset of blood lactate accumulation and marathon running performance. Sjödin B, Jacobs I. International Journal of Sports Medicine 2(1):23-26 (1981)
  14. A new approach for the determination of ventilatory and lactate thresholds. Cheng B, Kuipers H, Snyder AC, Keizer HA, Jeukendrup A, Hesselink M. International Journal of Sports Medicine 13(7):518-522 (1992)
  15. A review of the concept of the heart rate deflection point. Bodner ME, Rhodes EC. Sports Medicine 30(1):31-46 (2000)
  16. The surprising history of the "HRmax=220-age" equation. Robergs RA, Landwehr R. Journal of Exercise Physiology online (2002)
  17. Age-predicted maximal heart rate revisited. Tanaka H, Monahan KD, Seals DR. Journal of the American College of Cardiology (2001)
  18. Longitudinal modeling of the relationship between age and maximal heart rate. Gellish RL, Goslin BR, Olson RE, McDonald A, Russi GD, Moudgil VK. Medicine & Science in Sports & Exercise (2007)
  19. Age-predicted maximal heart rate in healthy subjects: The HUNT fitness study. Nes BM, Janszky I, Wisløff U, Støylen A, Karlsen T. Scandinavian Journal of Medicine & Science in Sports (2013)
  20. Heart rate response to exercise stress testing in asymptomatic women: the St. James Women Take Heart Project. Gulati M, Shaw LJ, Thisted RA, Black HR, Bairey Merz CN, Arnsdorf MF. Circulation (2010)
  21. Normal cardiopulmonary responses during incremental exercise in 20- to 70-yr-old men. Inbar O, Oren A, Scheinowitz M, Rotstein A, Dlin R, Casaburi R. Medicine & Science in Sports & Exercise (the abstract gives the slope only; the intercept is confirmed through Robergs and Landwehr) (1994)
  22. Accuracy of Commonly Used Age-Predicted Maximal Heart Rate Equations. Shookster D, Lindsey B, Cortes N, Martin JR. International Journal of Exercise Science (2020)
  23. Exercise intensity: How to measure it. Mayo Clinic
  24. Beta blockers: How do they affect exercise?. Mayo Clinic
  25. Target Heart Rates Chart (reviewed August 2024). American Heart Association (2024)
  26. Joe Friel's Quick Guide to Setting Zones. Friel J. TrainingPeaks Learn (reprints Friel's 2009 text; page updated July 2026)
Manish Kumar
Manish Kumar

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Disclaimer: This calculator is for informational and personal journaling purposes only. It logs measurements and compares them to published reference values. It is not health, medical, or nutrition advice.