How to Calculate Heart Rate Zones

In 1978, Victor Katch and colleagues put 31 people on a cycle ergometer and had each of them ride at 60, 70 and 80 percent of their own max heart rate. At 60 and 70 percent, only one rider was clearly past the point where blood acidity starts to climb. At 80 percent, 17 riders were above that point and 14 were at or below it. Every rider was holding the same relative heart rate, and the group split almost in half between two different kinds of exercise.

Most watches still build heart rate zones the way Katch's protocol did, as fixed percentages of a maximum. In 2025 a joint expert statement from the American College of Sports Medicine and Exercise and Sport Science Australia cited that same study and concluded that fixed percentages of maximal anchors, including percent of max heart rate and percent of heart rate reserve, "will cause individuals to exercise in different training intensity categories."

This guide shows how to do the arithmetic for every common zone model, then measures how wrong each one can be. Zone formulas carry two separate errors. The first is an estimated max heart rate, which typically misses by about 10 beats per minute. The second is larger and less discussed. Even with a perfectly measured max, the heart rate at your first threshold can sit anywhere from 60 to 90 percent of it. The later sections cover field tests that remove both errors, how Apple Watch and Titan set zones, and a 20-minute session that gets you most of the way there. The performance physiology guide explains the oxygen delivery and lactate physiology that the thresholds mark.

01The short answer

Calculating heart rate zones takes three steps.

1. Pick an anchor. Your max heart rate, your heart rate reserve (max minus resting), or your heart rate at a measured threshold.
2. Get the anchor's value. Measure it, or estimate it from a formula such as 208 − 0.7 × age from Tanaka and colleagues.
3. Multiply by the zone percentages. For percent of max, each boundary is max × percentage. For heart rate reserve, each boundary is resting + percentage × (max − resting).

A 40-year-old with no test data gets an estimated max of 180 bpm from Tanaka's equation. Using Polar's five zones of 50 to 60, 60 to 70, 70 to 80, 80 to 90 and 90 to 100 percent of max, zone 2 runs from 108 to 126 bpm. With a resting heart rate of 55 bpm, the same 60 to 70 percent applied to heart rate reserve gives 130 to 143 bpm. The two methods disagree by 17 to 22 beats on a zone with the same name, before anything has been measured.

That gap is typical. The rest of this article explains where each number comes from and which one to trust.

02Four ways to build zones

Every zone system combines an anchor with a set of percentages. The anchor decides how closely the zones follow your physiology. The percentages decide how many zones you get and where the labels fall.

Percent of max heart rate

This is the default on most consumer devices because it needs one number. Polar's zones run from 50 to 100 percent of max in five 10-point bands and suggest 220 minus age as "the simplest way" to estimate the max. Titan's defaults start at 53, 74, 81, 87 and 93 percent. The American College of Sports Medicine, in the table reproduced in the 2025 joint statement, classes 64 to 76 percent of max as moderate and 77 to 95 percent as vigorous.

The method assumes that a given share of max means the same effort for everyone. Katch's riders showed in 1978 that it does not, and the section on thresholds below shows how large the spread is.

Percent of heart rate reserve

Heart rate reserve is the span between resting and max. The Karvonen formula, from Karvonen, Kentala and Mustala's 1957 study, applies the percentage to that span and adds the resting rate back.

Target heart rate = resting + fraction × (max − resting)

The method has a sound physiological basis. David Swain and Brian Leutholtz tested 63 adults on a cycle ergometer in 1997 and found that percent of heart rate reserve tracked percent of oxygen uptake reserve almost exactly, with a mean slope of 1.00 and an intercept of −0.1. Against percent of VO2 max, the same data gave a slope of 1.12 and an intercept of −11.6. A treadmill study of 50 adults by the same group in 1998 found the same pattern. ACSM's intensity table uses 40 to 59 percent of reserve for moderate exercise and 60 to 89 percent for vigorous.

Reserve zones sit higher than percent-of-max zones, and the gap shrinks as intensity rises. For someone with a max of 185 and a resting rate of 50, 60 percent of reserve is 131 bpm, which is 71 percent of max, 11 points higher. At 90 percent of reserve the gap is under 3 points. Heart rate reserve mostly changes where your easy zones fall.

Percent of threshold heart rate

Threshold models anchor the zones to your heart rate at a sustained hard effort, usually lactate threshold heart rate (LTHR), close to the second threshold. Joe Friel's field test for LTHR is a solo 30-minute time trial run like a race, with the average heart rate of the last 20 minutes taken as the estimate. McGehee and colleagues compared the 30-minute time trial with a laboratory threshold in 27 competitive runners and triathletes in 2005, and the heart rate estimate carried a standard error of 8 bpm.

The percentages layered on top of LTHR are less settled than the test. Andrew Coggan's levels, published by TrainingPeaks, put Endurance, level 2, at 69 to 83 percent of threshold heart rate. Friel's running zones put zone 2 at 85 to 89 percent of LTHR, and his cycling zones put it at 81 to 89 percent. For an LTHR of 165 bpm, Coggan's zone 2 is 114 to 137 bpm and Friel's running zone 2 is 140 to 147 bpm. Both are called zone 2, both are anchored to the same measured threshold, and they do not overlap.

Coggan's levels also anchor to power for cyclists, as percentages of functional threshold power (FTP).

Friel splits Zone 5 further into 5a, 5b and 5c for threshold-plus, anaerobic capacity and sprint work.

Three physiological zones

Training intensity research mostly uses three zones separated by two measured boundaries. The 2025 ACSM and ESSA statement names them Low, below the first metabolic threshold, Moderate, between the first and second thresholds, and High, above the second threshold up to the work rate at VO2 max. The authors state that the "direct measurement of metabolic thresholds" is the "best and preferred method (where possible)" for defining intensity categories, and that current markers, including percent of max and percent of reserve, "do not achieve category-specific cardiovascular and metabolic responses in all (or even most) individuals."

The first threshold is the lactate threshold LT1 or the first ventilatory threshold VT1. The second is LT2, the maximal lactate steady state, critical power or the respiratory compensation point, depending on how it is measured. Polarized training and most intensity distribution studies are written in this model.

Stephen Seiler's version of the model uses the two thresholds as its only boundaries.

Seiler's 2010 review of nationally and internationally competitive endurance athletes found about 80 percent of training sessions performed at low intensity, around 2 mmol/L lactate, with about 20 percent dominated by high-intensity work such as intervals near 90 percent of VO2 max. Seiler and Kjerland's 2006 study of junior cross-country skiers showed the same low-intensity bulk. The model's value is its simplicity. Keep easy days easy and hard days hard.

Five-zone scales map onto the three. Tønnessen and colleagues published the scale that Olympic and world champion skiers trained by, with typical values averaged from the self-reported zone cut-offs of 29 elite cross-country skiers and a note that "individual adjustments are required."

Those percentages describe elite skiers on average. The five-zone labels on your watch map onto the three physiological zones only as well as your thresholds match that average.

03Heart rate zones by age

Most people searching for zones by age want a table. Here is one, built from Tanaka's 208 − 0.7 × age and Titan's default zone percentages, which sit close to the elite skiers' scale above. Each boundary is rounded to the nearest whole beat, and each zone starts one beat above the top of the one below it, as Titan calculates them.

Treat every cell as a starting estimate for an average person of that age. The next table shows what the same zone 2 looks like when the formula misses by 11 bpm, about one standard error, in either direction.

At every age, the low and high versions of zone 2 do not overlap. About one person in three sits farther from the formula than this table shows. The age column tells you less about your zones than those two error columns do.

04Max heart rate formulas and their error

The formula most people know has the weakest pedigree. Robert Robergs and Roberto Landwehr traced 220 minus age in 2002 to a 1971 review by Fox, Naughton and Haskell, whose figure plotted about 35 data points from roughly 11 references with no regression. When Robergs and Landwehr fitted a regression to those points, the standard error was 21 bpm. The max heart rate glossary entry tells that history in full.

Better equations now exist, and they agree closely with each other on the average.

Tanaka's group found no difference between men and women and no effect of habitual activity, and concluded that 220 minus age underestimates max heart rate in older adults. The HUNT Fitness Study behind Nes's equation also found no interaction with sex, activity, VO2 max or body mass index. Gulati's cohort of asymptomatic women given clinical stress tests found that the traditional formula overestimates max heart rate in women. The healthy-volunteer studies and the clinical study disagree about women, which is one more reason to measure.

What none of the formulas can do is predict one person. Nes and colleagues reported a standard error of 10.8 bpm around their line. Robergs and Landwehr found standard errors of 7 to 11 bpm across the literature. Kasiak and colleagues tested 13 equations against measured max in 4,043 runners and 1,026 cyclists in 2023 and found root mean square errors of 9.1 to 10.5 bpm, with Tanaka's among the most accurate. If the misses are roughly normal, a 10.8 bpm standard error means about two people in three land within 11 bpm of the formula and about one in twenty misses by more than 21 bpm. Robergs and Landwehr judged errors up to 8 bpm tolerable for setting training ranges. A typical formula error is larger than that.

What a max error does to each zone

A wrong max moves every boundary by the same fraction as the boundary's percentage. For a percent-of-max zone that starts at 74 percent, an 11 bpm error in max moves the start by 0.74 × 11, about 8 bpm. For heart rate reserve, the arithmetic gives the same result for the max term. Differentiate resting + f × (max − resting) and a change in max moves the boundary by f times the change. The reserve method does nothing to protect you from a wrong max.

Compare those shifts with the width of the zones themselves. At a max of 185 bpm, Titan's default Zone 2 is 13 beats wide and Zones 3 and 4 are 11 beats wide each. An error of one standard error in max moves the upper zone boundaries by close to a full zone. A steady run that belongs in Zone 2 reads as Zone 3, or the other way around, with nothing about the run itself having changed.

Resting heart rate is the easy input. Its effect on a reserve boundary is (1 − f) times its error, so a resting rate that is 5 bpm off moves a 70 percent reserve boundary by 1.5 bpm. Whether you use a seated morning reading or the overnight value your watch reports matters far less than the max.

The bigger error is where your thresholds sit

Suppose you measure your max perfectly. The zones can still be wrong, because the percentages assume your thresholds sit at a typical share of max.

Iannetta and colleagues tested 100 adults, 46 women and 54 men, in 2020. They measured each person's lactate threshold with a ramp test and their maximal lactate steady state with repeated 30-minute rides. The lactate threshold fell anywhere from 60 to 90 percent of max heart rate. Maximal lactate steady state fell anywhere from 75 to 97 percent. Women reached both at a higher share of their max than men. The authors concluded that fixed percentages "conform poorly to exercise intensity domains and thus do not adequately control the metabolic stimulus."

At a max of 185 bpm, 60 to 90 percent of max is 111 to 167 bpm. That is a 56-beat range for the heart rate at the top of your easy zone, five times wider than the formula error on either side of the average. Katch's 1978 result is the same finding at a single intensity. Scharhag-Rosenberger and colleagues found it again with oxygen uptake in 2010. Twenty-one healthy men rode for an hour at 60 percent of VO2 max, and their blood lactate ranged from 0.7 to 5.6 mmol/L. At 75 percent it ranged from 2.2 to 8.0 mmol/L. The spread held even within subgroups of similar fitness.

Jamnick and colleagues' 2020 review in Sports Medicine judged that fixed percentages of maximal anchors have "little merit" for producing domain-specific responses, and found reasonable support for LT1, the gas exchange threshold and the ventilatory threshold as the boundary between moderate and heavy exercise. The practical ranking follows from that. A formula max with default percentages is a guess stacked on a guess. A measured max with default percentages removes the smaller error. Zones anchored to measured thresholds remove both.

05How to find your real max

A max test is an all-out effort. The ACSM's preparticipation screening, updated by Riebe and colleagues in 2015, rests on three questions: how active you are now, whether you have signs or symptoms of cardiovascular, metabolic or renal disease or a known diagnosis, and how hard you plan to exercise. If you are inactive, have one of those conditions, or have had chest pain, fainting or unusual breathlessness during exercise, see a clinician before a maximal effort. A supervised exercise test with ECG is the right tool in that case.

For a healthy, trained person, the field and the lab give similar answers. Boudet and colleagues put 16 endurance athletes through five exhaustive efforts in each of three settings, the lab, field tests and competition. Mean peaks were 194.3, 193.8 and 192.3 bpm, with no significant difference. The highest value came from the lab for 5 athletes, from field tests for 7 and from races for 6, and the same athlete's peak varied by about 6 bpm between efforts. The authors recommended the median of several maximal efforts over a single peak. In their athletes the median max sat 7.6 bpm below the single highest reading.

That finding argues for collecting more than one number. A usable field protocol is a 15 to 20 minute warm-up followed by a hill or treadmill effort that builds over several minutes and ends with two to three minutes as hard as you can go. On a trainer, a ramp can start at 100 W and add 20 W each minute until you cannot hold cadence above 60 rpm. On a treadmill, add 0.5 km/h or 1 percent grade each minute. Record it with a chest strap. In Gillinov and colleagues' 2017 comparison of wrist monitors against ECG in 50 adults, a chest strap agreed with ECG at a concordance of 0.996 and the Apple Watch at 0.92, and no wrist device was accurate on an elliptical with moving arm levers. Apple's own guidance is to wear the watch snugly and to pair a Bluetooth chest strap when the optical sensor cannot get a consistent reading.

Test in the sport you train. Millet, Vleck and Bentley's 2009 review of triathletes found that heart rate differs between cycling and running at both maximal and submaximal intensities. The size of the gap varies by study and by athlete. Basset and Boulay found only about 4 bpm between treadmill and cycle ergometer at matched percentages of VO2 max in 18 trained athletes. Persinger and colleagues, testing 16 healthy volunteers on both, found the ventilatory threshold at 89 percent of peak heart rate on the treadmill and 82 percent on the cycle ergometer. If most of your training is cycling, set your zones from a cycling test.

You may also have your max on record already. The finish of a 5K, a hill repeat that ended in a sprint, or the last interval of a hard session can reach it. Check any candidate against the seconds around it. A value that appears for a moment, jumps well above the readings before and after, or exceeds anything you have recorded in a race is more likely a sensor error than a new max.

06How to find your thresholds in the field

A laboratory step test with blood lactate or gas analysis gives the most direct answer. The lactate threshold entry covers those methods and their disagreements. Several field tests get close enough to set training zones.

The talk test for your first threshold

The talk test asks whether you can speak comfortably. During graded exercise you read a short passage aloud near the end of each stage and rate it as comfortable, not sure, or not comfortable.

Persinger and colleagues ran the test alongside gas analysis on a treadmill and a cycle ergometer in 2004. The stage where speech first became uncertain matched the ventilatory threshold on both. When speech was no longer comfortable, intensity was consistently above it. Quinn and Coons tested 15 young adults in 2011 and found the last comfortable stage at 64 percent of VO2 max, 82 percent of max heart rate and an RPE of 12, values closer to their measured lactate threshold than to their ventilatory threshold. Foster and colleagues showed in 2008 that the talk test moved with the ventilatory threshold when the threshold was pushed down by blood donation or up by training. They also found that, above the threshold, it took more than 2 minutes on average for talking to become uncomfortable, so short stages can make the test read high.

The joint ACSM and ESSA statement adds a limit worth keeping. Comfortable speech can end before the first threshold in inactive people and continue well past it in trained athletes. For a trained athlete, the last clearly comfortable stage is a conservative ceiling for easy work.

The heart rate drift test

Steve House's drift test at Uphill Athlete estimates the aerobic threshold from cardiovascular drift. After a warm-up of about 15 minutes, you hold a steady conversational pace for 40 to 60 minutes on a treadmill or a flat course such as a track, and compare average heart rate in the two halves. Divide the second-half average by the first-half average, subtract 1 and multiply by 100. Drift of 3.5 to 5 percent means your starting heart rate was close to your aerobic threshold. Under 3.5 percent means you can retest about 5 bpm higher, and over 5 percent means you started above it. The article recommends a chest strap or arm band and says wrist monitors are not yet accurate enough for this test.

The test works because heart rate climbs during steady work even at a constant pace. Coyle and González-Alonso described cardiovascular drift in 2001 as a progressive fall in stroke volume after 10 to 20 minutes of exercise, driven mainly by the rising heart rate. The article rules out trails, because heart rate changes every time the grade changes. Heat also adds drift, so run the test in cool, steady conditions.

The 30-minute time trial for your second threshold

Friel's 30-minute solo time trial, with a lap button pressed at 10 minutes and the average of the final 20 minutes taken as LTHR, estimates the second threshold. McGehee's 8 bpm standard error means roughly one runner in three lands more than 8 bpm from their laboratory threshold heart rate. Pace it evenly. A fast start and a fade produce a lower average that looks like a lower threshold.

Power tests for cyclists

Cyclists with a power meter can anchor zones to power as well as heart rate. The 20-minute FTP test is a solo all-out effort after a thorough warm-up, with FTP taken as 95 percent of the average. The lactate threshold entry covers how far that conversion can miss.

Vanhatalo, Doust and Burnley showed in 2007 that power in a 3-minute all-out cycling effort settles to a steady level over roughly the last 45 seconds. That end power matched critical power measured the conventional way to within about 5 W in 8 of 10 subjects. Work done above the end power estimates W′, the finite amount of work available above critical power.

Heart rate variability during exercise

A newer method reads the beat-to-beat pattern during a ramp. DFA alpha 1, a fractal index of heart rate variability, falls as intensity rises. Rogers and colleagues found that DFA alpha 1 reaching 0.75 on a treadmill ramp matched the first ventilatory threshold in 15 participants, at an average heart rate of 154 bpm against 152 bpm by gas exchange. A value of 0.5 tracked the second threshold less tightly, 171 against 174 bpm with a correlation of 0.78. The method needs clean beat-to-beat data from a chest strap and an app that computes it.

Perceived effort as a cross-check

The joint statement proposes perceived-effort anchors for its categories on the 6 to 20 RPE scale, 10 to 11 for Low, 12 to 14 for Moderate and 15 to 16 for High. The authors also report that individual RPE at the first threshold ranges from about 7 to 14, and at the second from about 9 to 17. RPE is a useful check on a heart rate zone and a poor substitute for a threshold test.

07What is zone 2 heart rate

Zone 2 has three common meanings. On a five-zone watch it is a band of max heart rate, 60 to 70 percent on Polar and 74 to 80 percent in Titan by default. In the popular endurance and longevity sense, it is the top of the easy range, the highest intensity just below the first lactate threshold. In training research, zone 2 is the band between the two thresholds, the moderate intensity that polarized programs keep small. The zone 2 glossary entry covers each definition and the evidence for zone 2 training.

For most people asking the question, the useful answer is physiological. Your zone 2 ceiling is your heart rate at LT1 or VT1. Iannetta's data put that ceiling anywhere from 60 to 90 percent of max, so a population answer will be wrong for many people. For a 40-year-old with a 180 bpm max, that spans 108 to 162 bpm. The talk test or the drift test above finds your own number.

Phil Maffetone's 180 Formula is the most searched shortcut for this ceiling. It starts at 180 minus age, then subtracts 10 for recovery from major illness or regular medication, subtracts 5 for injury, regression or frequent illness, adds nothing for consistent training, and adds 5 for two or more years of progress without problems. Maffetone presents the result as a maximum aerobic heart rate. It is another age-based estimate, so it inherits the spread Iannetta measured. Use it as a starting guess to check with a talk or drift test.

The endurance training guide covers how much zone 2 work to do and how to check your distribution against a polarized or pyramidal plan.

08Why your zone on a given day moves

Even a well-calibrated zone describes heart rate under typical conditions. Several things change heart rate at the same effort.

Day-to-day variation. Lamberts and Lambert measured 38 people over four days in 2009. Heart rate at a fixed workload varied least, about 3 bpm, at 85 to 90 percent of max, and varied more at lower intensities. A 3 bpm wobble is about a quarter of a Titan zone at a 185 max.

Drift. In a long steady session, heart rate rises at the same pace, as described above. A run that starts at the top of Zone 2 can end in Zone 3 without any change in muscle work.

Lag. Heart rate trails changes in work rate. Coggan notes that in short VO2 max efforts the average heart rate may never reach the target range, because heart rate responds slowly and cannot rise past your max. For intervals of a few minutes or less, pace or power is the better target and heart rate zones describe the steady parts of the session.

Sport. Thresholds and max can sit at different heart rates in running and cycling, as Persinger and Millet found. One set of zones fits the sport it was measured in best.

Medication. Drugs that act on heart rate, such as beta-blockers, change the relationship between effort and heart rate. Polar's guide advises consulting a healthcare provider before setting zones if you take medication or have a heart condition, and that applies to any zone system.

09How Apple Watch sets zones

Apple's user guide describes Heart Rate Zones as "a percentage of your maximum heart rate" that are "automatically calculated and personalized using your health data." Zones appear only if your date of birth is entered in the Health app on iPhone. Apple does not publish the formula and does not say in that guide whether resting heart rate enters it.

You can override the automatic zones. On the watch, open Settings, then Workout, then Heart Rate Zones, and choose Manual. On iPhone, the same setting is in the Watch app under My Watch, then Workout, then Heart Rate Zones. Manual mode lets you set lower and upper limits for Zones 2, 3 and 4. Zones 1 and 5 cannot be edited directly.

During a cardio workout, turning the Digital Crown to the Heart Rate Zone view shows your current zone, heart rate, time in that zone and average heart rate. Afterward, the Fitness app on iPhone shows estimated time in each zone under the workout's heart rate details.

Wrist accuracy is adequate for steady running and cycling. In Zhang and colleagues' 2020 meta-analysis of 44 studies, wrist devices averaged a bias of −0.51 bpm on treadmills, −4.55 bpm during cycling and −7.26 bpm during resistance training, with the resistance training error growing by about 3 bpm for every 10 bpm rise in heart rate. For zone work in running, the wrist is close enough. For hard intervals, lifting and a max test, use a chest strap.

10How Titan sets and uses your zones

Titan calculates its own zones from the heart rate samples in Apple Health. Zones you set on Apple Watch do not change Titan's, and Titan's do not change Apple's, so the zone on your wrist and the zone Titan assigns to the same minute can differ.

Where the settings live

Tap your avatar at the top left of Today to open You, then tap the Your Training tile. The Heart Rate section holds the Use Custom Max Heart Rate toggle, the Max Heart Rate value, the Heart Rate Zones editor and a summary of each zone in bpm. The heart rate zones help article documents each control.

How Titan chooses your max

With Use Custom Max Heart Rate off, Titan compares two numbers and uses the higher one. The first is the single highest heart rate sample in Apple Health over the last 30 days, from the heart rate sources you allow under data sources. The second is 220 minus your age, from the date of birth in Apple Health. The Max Heart Rate row shows the value Titan is using, and the note under the section shows your 30-day max.

That rule has two consequences.

• The age formula acts as a floor. A quiet month without hard efforts does not pull your zones down. The floor is 220 minus age, which sits above Tanaka's estimate before 40 and below it after. A 25-year-old gets a floor of 195 bpm, where Tanaka predicts about 190.
• A race sets your zones for a month. A true max effort becomes your max for 30 days, then drops back to the next-highest recent peak or the age floor.

If you know your max from a test, turn on Use Custom Max Heart Rate and set it with the stepper, which moves in 1 bpm steps from 80 to 240 bpm and starts at 180. Titan keeps the resolved max and zone thresholds for up to seven days and recalculates immediately when you change the custom max or edit a zone. When the saved thresholds change, a Heart Rate Zones Updated card on Today shows the previous and new upper limit of each zone.

How Titan draws the zones

Titan uses the percent-of-max model with five zones named Very Light, Light, Moderate, Hard and Maximum. By default they start at 53, 74, 81, 87 and 93 percent. Each zone runs to one percent below the start of the next, and Titan rounds each boundary to the nearest whole bpm. Every reading lands in a zone. Heart rate below the Zone 1 start counts as Zone 1, and anything above the top of Zone 4 counts as Zone 5, including readings above your max. If Titan has no custom max, no heart rate from the last 30 days and no date of birth, it uses fixed thresholds, with Zone 1 ending at 132 bpm and Zone 5 starting at 168 bpm.

Titan does not use resting heart rate in its zones. If you prefer heart rate reserve, you can reproduce it by converting each reserve percentage into a percentage of max.

Percent of max = resting ÷ max + fraction × (1 − resting ÷ max)

For a max of 185 and a resting rate of 50, 50, 60, 70, 80 and 90 percent of reserve work out to 64, 71, 78, 85 and 93 percent of max. Enter those as the zone starts and Titan's zones match Karvonen zones for those inputs. Titan shows your RHR Baseline in the Your Fitness section of You. Redo the conversion if your resting rate changes by more than a few beats.

What the zones feed

Zone time drives three parts of the app.

Training load and Exertion. Titan weights each workout minute by its zone number, one point for a Zone 1 minute up to five for a Zone 5 minute. The weighted total is your daily training load and feeds your Exertion score. If the heart rate samples linked to a workout cover less than 70 percent of its duration, Titan also reads samples between the workout's start and end. A workout with no heart rate at all gets a fallback load from its duration and activity type.

Training load focus. Trends groups zone-weighted load into Low aerobic from Zones 1 and 2, High aerobic from Zone 3 and Anaerobic from Zones 4 and 5. When Zone 3 starts near your first threshold and Zone 4 near your second, these three groups match the three physiological zones.

Time in zone. The Heart Rate Zones card on Today shows your workout minutes in each zone. The Cardio distribution charts in Trends plot Zones 2 to 5 and leave out Zone 1.

Because load weights each zone by its number, a boundary error becomes a load error. Take a 60-minute run at a steady 145 bpm. With a measured max of 190, Titan's Zone 2 runs from 140 to 152 bpm and the run scores 120. With a predicted max of 178, Zone 2 ends at 142 and the same run lands in Zone 3, scoring 180. The same run adds 50 percent more load, and the difference comes entirely from the max.

Matching Titan's zones to your thresholds

Once you have threshold heart rates, convert each to a percentage of your max and move the zone starts. Open the Heart Rate Zones editor from Your Training. Each zone has a stepper that moves its start by 1 percent, and each start must stay above the one before it, so lower Zone 2 first when you need to move Zone 3 below its default. Tap the checkmark to save.

Take a runner with a measured max of 188, an LT1 of 141 bpm from a talk test and an LT2 of 168 bpm from a 30-minute time trial. LT1 is 75 percent of max, so set Zone 3 to start at 76 percent and Zone 2 ends at 141 bpm. LT2 is 89.4 percent of max, so round up and set Zone 4 to start at 90 percent, which puts the first Zone 4 beat at 168 bpm. Set Zone 2 to start about 10 points below Zone 3, at 66 percent. Low aerobic now means below this runner's first threshold, High aerobic means between the two, and Anaerobic means above the second.

Titan keeps one set of zones for every activity. If you both run and ride, set them from the sport you do most, or from the one where zone accuracy matters to you.

11Set your zones in 20 minutes

This is the fastest path to zones anchored to your own first threshold. It takes one 20-minute session and five minutes in the app. It assumes you are healthy, already exercise regularly, and have answered the screening questions above.

Before you start. Pair a chest strap with your watch. Use a treadmill at 1 percent grade or an indoor trainer, so the workload stays exact. Choose a short passage to read aloud, about 30 to 40 words, and use the same one at every stage.

Minutes 0 to 5. Warm up at an effort that feels very easy.

Minutes 5 to 20. Run five 3-minute stages, each slightly harder than the last. On a treadmill, add 0.5 km/h per stage. On a trainer, add 15 to 20 W. Pick a first stage you are sure is conversational. In the last 30 seconds of each stage, read the passage aloud and rate it as comfortable, not sure or not comfortable. Note your heart rate at the end of the stage. Three-minute stages give the talk test the time Foster found it needs to turn negative above the threshold.

Read the result. Your heart rate at the last comfortable stage is your estimated first threshold and your zone 2 ceiling. The first not-sure stage marks the start of moderate work. If every stage felt comfortable, repeat the session another day starting at your final pace. If the first stage was already uncertain, start slower next time.

Minutes 20 to 25, in Titan. Open You, then Your Training. If you have a measured max from a race or a max test, turn on Use Custom Max Heart Rate and enter it. Otherwise check the auto value against Tanaka's 208 − 0.7 × age and your hardest recent races, and set a custom max if the auto value disagrees with both. Divide your first-threshold heart rate by your max, then set Zone 3 to start one percent above that share and Zone 2 about 10 points below Zone 3. Save.

Later. Add the second threshold with a 30-minute time trial on another day and set Zone 4 to start at it. Confirm the first threshold with a drift test when you have an hour, since drift and the talk test measure the same boundary in different ways. If the two disagree by a few beats, use the lower number for easy days.

12When to recalculate

Thresholds move with training. A rising first-threshold heart rate, or a faster pace at the same heart rate, is the clearest sign your aerobic base is improving. Retest after a block of six to eight weeks, after a long break, after illness, and after any change in a medication that affects heart rate. Repeat each test under the same conditions, with the same course, time of day, temperature, fueling and rest, so that a change in the result reflects a change in you.

Max heart rate moves slowly with age, by 0.64 to 0.7 bpm per year in the large studies. Recheck it once or twice a year, and whenever a race or test produces a clean peak above your current setting. If you leave Titan in auto mode, watch the Heart Rate Zones Updated card. It tells you when a new peak has moved every zone.

The TRIMP post explains other ways to turn heart rate into training load, and the resting heart rate guide covers the other end of the heart rate range.

13References

• Apple (accessed 2026). View Heart Rate Zones on Apple Watch. Apple Watch User Guide. https://support.apple.com/guide/watch/view-heart-rate-zones-apd897dccddf/watchos
• Apple (accessed 2026). Get the most accurate measurements using your Apple Watch. Apple Support. https://support.apple.com/en-us/105002
• Basset FA, Boulay MR (2000). Specificity of treadmill and cycle ergometer tests in triathletes, runners and cyclists. European Journal of Applied Physiology 81(3):214-221. https://doi.org/10.1007/s004210050033
• Bishop DJ et al. (2025). Physical activity and exercise intensity terminology, a joint American College of Sports Medicine (ACSM) expert statement and Exercise and Sport Science Australia (ESSA) consensus statement. Medicine and Science in Sports and Exercise 57(11):2599-2613. https://doi.org/10.1249/MSS.0000000000003795
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