How Diastra draws your heart rate bands, and the study behind every edge

Where does Diastra get your max heart rate?

Every band is a share of your max heart rate. Diastra checks four places for that number in this order. It also tells you which one it used.

1. A guided max test. You run a guided test, and Diastra reads the highest heart rate you held during the effort.
2. A number you type. You may know your max from a race or a lab test. When you have both a test and a typed number, the newer one wins.
3. Your own workouts. Diastra reads every workout your Apple Watch saved in Apple Health and finds the highest heart rate each one held.
4. An age estimate. Diastra estimates your max as 208 minus 0.7 times your age until one of the above replaces it. This is the Tanaka formula.

A workout peak has to pass two checks before Diastra uses it. Your heart has to hold the number for at least ten seconds across several readings, so a one-reading spike from the sensor is ignored. Then a second workout has to reach within 8 beats of the same peak.

The age estimate comes from Tanaka and colleagues. They pooled 351 studies with 18,712 people and then checked the result in a lab with 514 more.^[1] They also found that the older 220 minus age formula reads too low for older adults.^[1] A 60-year-old gets 160 from 220 minus age and 166 from Tanaka. The max heart rate formulas page compares the formulas in full.

Any age formula describes a group. A study of 3,320 healthy adults found that an age formula typically missed a person's measured max by about 11 beats.^[2] So Diastra drops the estimate as soon as a typed number, a higher test peak or a confirmed higher workout peak comes in.

Why does a low workout peak not replace the age estimate?

Most runs never reach your max. An easy week can top out at 150 beats a minute when your heart can reach 185. That peak shows how hard you ran that week. It says nothing about how high your heart can go.

So a workout peak replaces the age estimate only when it is higher than the estimate. Say you are 40. The estimate is 180. If your hardest workouts top out at 172, Diastra keeps 180. If two hard workouts reach 186 and 184, Diastra uses 186.

A guided test follows the same rule. Its peak replaces your max only when it is higher than the age estimate and higher than the max Diastra already uses. A number you type is the one exception. Diastra uses it as typed.

Diastra never lowers a measured max because months went by. Your max changes only when a harder effort, a test or a typed number gives a new one. The page on finding your max on Apple Watch shows how to get a real max into your workouts.

Where does Easy start and stop?

Easy is the band most runners call Zone 2. It is the pace you can hold a conversation at. In Diastra it runs from 60% of your max up to where the first lactate threshold falls on average. That threshold is the point where lactate in your blood starts to climb.

The top edge comes from blood tests on 165 recreational runners. Nuuttila and colleagues found the first threshold at 78.9% of max for men and 83.6% for women. The average for everyone was 80.7%.^[3] The authors wrote that the gap suggests men and women need different anchors.^[3] Diastra follows those averages. Easy ends at 79% of your max for men and 83% for women. When sex is not given, Easy ends at 80%.

Breathing tests give a wider range. Benítez-Muñoz and colleagues tested 1,272 adults on a treadmill. Their group averages for the first threshold ran from 74.6% of max in the least-trained men to 82.9% in the most-trained women.^[4] Esteve-Lanao and colleagues tested 1,411 trained distance runners and found it at 85.1% of peak heart rate on average.^[5] The three studies tested more than 2,800 people in all. Women came out higher than men in all three.^[3][4][5] That difference is why Diastra splits Easy by sex.

The bottom edge is 60% of max. Diastra does not credit heart rate below that as Easy. The Zone 2 heart rate page explains how this Easy band compares with the Zone 2 on most watch charts.

How far can your own threshold be from the edge?

A fixed edge is an average. Your own threshold can be far from it.

Nuuttila's team tested this directly. They placed each runner's first threshold at the average share of max for that runner's sex and compared it with the blood test. The fixed edge landed within about 16 beats of the real first threshold for 95 of every 100 runners. The miss at the second threshold stayed within about 9 beats.^[3] These are best-case numbers, because every runner's max was measured in the lab.^[3]

An average edge also splits runners into two groups. A fixed 80% of max left 57 of every 100 runners below their first threshold and put the other 43 above it.^[3]

Iannetta and colleagues found an even wider spread in 100 adults. Their first lactate threshold fell anywhere from 60% to 90% of max.^[7] Maximal lactate steady state is the hardest effort where blood lactate still holds level. In the same people it fell anywhere from 75% to 97% of max.^[7]

This spread is why Diastra never asks you to run harder inside Easy. Your own threshold could be 16 beats under the edge. A push toward the top of the band could take you past it. If the top of Easy feels hard, run slower.

The Easy edges come from running studies, and a bike gives lower numbers. A study tested 143 triathletes on a treadmill and on a bike. Their heart rate at the first threshold came 10 to 13 beats lower on the bike.^[6]

What is the gray band?

The gray band is the space between the top of Easy and 87% of your max. For men it runs from 79% to 87%. For women it runs from 83% to 87%. Nobody sets its edges. They move whenever the top of Easy or the floor of Threshold moves.

Gray minutes are real training, and they show up in your week as gray. They do not fill your Easy, Threshold or VO₂max targets. Gray minutes don't glow.

Where does Threshold start and stop?

Threshold is the fastest pace you can hold before fatigue stacks up quickly. In Diastra it runs from 87% of your max to just under 92%.

Both edges match the zone scales that coaches use. Olympiatoppen is Norway's Olympic sports center. Its scale sets the fourth zone at about 87% to 92% of max and the fifth at about 92% to 100%.^[8] A 2025 survey asked endurance coaches and athletes where their own zones start. Runners in the survey put the floor of zone 4 at 86.6% of max and the floor of zone 5 at 92.3%.^[9]

The band is drawn around the second lactate threshold. That is the point where lactate builds faster than your body clears it. Nuuttila's runners reached it at 90.6% of max on average. Women reached it at 91.7% and men at 89.9%.^[3] Women came out a little higher here too. All three numbers fall inside the band, so Threshold uses one band for everyone.

Breathing tests place the second threshold higher. Benítez-Muñoz's group averages ran from 90.6% to 95.6% of max.^[4] Esteve-Lanao's trained runners averaged 93.5% of peak heart rate.^[5] Diastra keeps the top of Threshold at 92%. That line matches the zone scales, and the blood-test averages fall under it.

Where does VO₂max start?

VO₂max is your aerobic capacity. It is the most oxygen your body can use when you go all-out. The VO₂max band starts at 92% of your max. It has no top edge and runs up to your own max.

The 92% line is the floor of the highest heart rate zone in both zone scales.^[8][9] Every group of coaches and athletes in the survey put that floor between 92.1% and 92.9% of max.^[9]

Interval research agrees with it. Helgerud and colleagues trained 40 men three times a week for eight weeks. One group ran four 4-minute intervals at 90% to 95% of max with 3 minutes of easy running between them. That group raised VO₂max by 7.2%. Groups that did the same total work at 70% or 85% of max raised it less.^[10] Diastra's 92% line falls inside that 90% to 95% range.

The VO₂max band is a heart rate band. It does not measure oxygen. A study of 162 young adults found that 92% of max heart rate came at about 85% of VO₂max.^[11] Fleckenstein and colleagues measured heart rate and oxygen in the same sessions with 12 highly trained runners. Short 30-second intervals gave 820 seconds above 90% of max heart rate, and 3-minute intervals gave 545.^[12] The same short intervals gave only 201 seconds above 90% of VO₂max, and the 3-minute intervals gave 328.^[12] Minutes in the VO₂max band show how long your heart worked near its max. Lab studies that report time at VO₂max measure oxygen, which is a different number.

Why are the edges rounded up to whole beats?

Your watch reports whole beats. The edges are shares of your max, so they often land between two whole numbers. Diastra rounds every edge up.

Take a 40-year-old woman with a max of 180. 87% of 180 is 156.6. Her Threshold band starts at 157, because 156 is only 86.7% of 180. Diastra grades every reading against the exact share. Rounding up makes each printed edge the first whole beat that grades in that band.

Here are her four bands.

A 40-year-old man with the same max sees Easy end at 142 and the gray band start at 143.

What do the bands look like at each age?

This table uses the Tanaka estimate for max heart rate. A max from your own workouts, a test or a typed number moves every row.

Beats a minute, with max heart rate estimated from age (Tanaka). A measured max moves every band.

How sure is each edge?

The heart rate zone calculator draws these edges for any age and sex.

What Diastra does with these bands

Diastra reads every workout your Apple Watch saved in Apple Health. It finds your max from those workouts, a guided test or a number you type, and it tells you which. It draws Easy, Threshold and VO₂max from that max, with the top of Easy split by sex. The watch holds you in your band with a tap whenever you drift out. Diastra credits only the minutes that held. Over the weeks it shows whether your training is working, in three words. Getting fitter. Holding steady. Slipping. Diastra works without an account.