What is your lactate threshold heart rate?

Why does "threshold" mean so many different things?

Ask three coaches what threshold means and you can get three answers. One talks about the pace where running stops feeling easy. Another talks about the hardest pace you can hold for a long time. A third gives you a heart rate from a test.

All three are talking about something real. Your body has two lactate thresholds. Each one has picked up several names over the years. Most of the confusion goes away once you know which threshold a name points at.

What are the two lactate thresholds?

Lactate is a substance your muscles make all the time. Physiologists now describe it as a key energy source for the body^[4]. Your muscles make more lactate when you run harder, and the level in your blood starts to change.

The first threshold is where lactate in your blood starts to rise above its resting level^[5]. A common rule of thumb says you can still talk in full sentences below it. Most easy running happens below this line.

The second threshold is the hardest effort where your body still clears lactate as fast as your muscles make it^[5]. Above it lactate keeps building until you have to slow down. The same rule of thumb says talk shrinks to a few words at a time here. Well-trained runners in one study held this effort for about 80 minutes before they had to stop^[2].

The term lactate threshold heart rate (LTHR) almost always means your heart rate at the second threshold. That number is what this page is about.

Why are there so many names for each threshold?

The names come from different tests and different decades. A blood test reads lactate from a drop of blood. A breathing test reads the air you breathe out through a mask. Each test finds its own version of each threshold, and each lab gave its version a name. One review counted 25 different ways to define a lactate threshold^[5].

Anaerobic threshold is the name that causes the most trouble. The physiologist Karlman Wasserman used it for the point where blood lactate starts to rise in a test that keeps getting harder^[4]. That point matches the first threshold. Some coaches and training plans use the same words for the second threshold. The name also carries an old idea that muscles run short of oxygen at that point. Research no longer supports that idea^[4].

Maximal lactate steady state is the fastest steady effort where blood lactate stays flat. Labs usually find it with four or five 30-minute runs at different fixed speeds on separate days^[6]. Critical speed comes from a different method. It uses how long you can hold several different fast speeds. Critical speed comes out a little faster than the maximal lactate steady state, and an effort at critical speed lasts only about 20 to 30 minutes. Physiologists still argue about which marker best shows the top of steady effort^[6].

Where does threshold fall as a share of max heart rate?

Three lab studies give a clear picture of the average and a wide picture of the spread.

• 165 recreational runners. Blood tests on a treadmill put the second threshold at 90.6% of max heart rate on average^[1]. It came at 91.7% of max for women and 89.9% for men. The first threshold came at 80.7% of max on average, with 83.6% for women and 78.9% for men.
• 22 well-trained distance runners. Their maximal lactate steady state came at 89% of max heart rate for men and women alike^[2].
• 100 adults. The maximal lactate steady state of 46 women and 54 men landed anywhere from 75% to 97% of max heart rate from one person to the next^[3]. The first threshold ranged from 60% to 90%. Both came at a higher share of max in women.

The averages agree closely. They put the second threshold near 90% of max heart rate, between about 89 and 92%.

The spread is the part a chart leaves out. In the study of 165 runners, a guess from the average for each sex came within about 9 beats a minute of the real second threshold for 95 in 100 runners^[1]. The typical miss was about 3 beats, and it went in both directions. Take a man whose max is 190. The men's average of 89.9% puts his threshold heart rate near 171. If he is like 95 in 100 of the runners in that study, his real number falls somewhere from about 162 to 180.

How does Diastra's Threshold band match the second threshold?

Diastra's Threshold band runs from 87% of your max heart rate up to one beat under 92%. Each edge rounds up to a whole beat. A runner with a max of 190 gets a Threshold band from 166 to 174 beats a minute.

Every study average above lands inside that band. The 90.6% from 165 runners falls between 87 and 92%. So do the 91.7% for women and the 89.9% for men. The 89% from well-trained runners falls inside it too.

Two bands frame it. Below Threshold is the gray band, which runs from the top of Easy up to 87% of max. Above Threshold is VO₂max, from 92% of max up to your max. Easy is Diastra's name for the Zone 2 most runners know. The top of Easy follows the first threshold and is split by sex. It comes at 79% of max for men, 83% for women and 80% for anyone who does not say.

The Threshold band is a range drawn around the research averages. It does not measure your own threshold, and the spread in the studies is wider than the band. A range gives a threshold run a target wide enough to hold while heart rate climbs through a long effort. Every edge moves when your max moves. How Diastra draws your bands lists every edge and the study behind it.

How can you test your own threshold heart rate?

Start with an easy warm-up. Then run the field test the coach Joe Friel describes for runners^[8].

1. Run 30 minutes alone at the hardest effort you can hold for the whole time. Friel says to run it with no training partners and not in a race.
2. Press the lap button on your watch at 10 minutes.
3. When you finish, read your average heart rate for the last 20 minutes. Friel calls that number an approximation of your LTHR.

Friel adds that the test gets more accurate each time you do it, because you learn to pace the start better.

Leaving out the first 10 minutes keeps the slow start out of the number. In a treadmill study of 24 men, heart rate made about two thirds of its change in about a minute after each change in speed^[9]. By that math it takes about 3 minutes to get most of the way to its new level. A flat route or a track helps. Use the same route and the same time of day when you retest, so the two numbers compare.

Your watch may already hold this test. Look for a run where you went hard and steady on your own for about 30 minutes. The average heart rate from minute 10 to the end gives you the same estimate. The run has to be one unbroken, all-out steady effort for the number to mean anything.

An interval session cannot do this job. The breaks between repeats give you rest. That rest lets you hold a higher heart rate in each repeat than you could hold in one unbroken effort. A threshold number taken from intervals reads too high.

Test in the sport you train in. In 143 triathletes who did a breathing test on a treadmill and on a bike, the men's heart rate at the second breathing threshold was 172 running and 163 cycling^[10]. The women's was 175 running and 169 cycling. A threshold from a bike test reads low for running.

Friel then sets his running zones as shares of LTHR instead of shares of max heart rate. His Zone 4 runs from 95% to 99% of LTHR and his Zone 5a from 100% to 102%^[8]. A chart built on max heart rate and a chart built on LTHR start from different numbers. The same zone name can point at different heart rates in each one.

How does threshold change with training?

Threshold matters because it shapes how much of your fitness you can use for a long time. A review of champion endurance athletes names three main factors in performance. They are VO₂max, the lactate threshold and efficiency^[7]. VO₂max and the threshold together set how much oxygen you can keep using through a long effort. Efficiency then decides how much speed you get from that oxygen^[7].

Training can move the threshold. In one small study, eight well-trained runners added one 20-minute run a week at about their threshold speed^[11]. After 14 weeks they could run faster before their blood lactate reached the same level. Their VO₂max did not change.

The biggest gains go to people who start out inactive. A review of 34 studies found large threshold gains in inactive people who began training^[12]. People who already trained gained less, and their gains were too small to be sure of.

Pace is the easiest way to see the change for yourself. If you run faster at the same threshold heart rate than you did a few months ago, your threshold has moved.

A heart rate number alone can mislead. Your threshold heart rate is a share of your max, and max heart rate varies a lot from person to person. In a Norwegian study of 3,320 healthy adults, an age formula missed people's real max by a typical 10.8 beats a minute^[13]. Max differed only a little between fit and less fit people of the same age. So a friend with a higher threshold heart rate is not fitter for that reason alone. Compare yourself with your own past tests, run the same way each time. Max heart rate by age shows how wide that spread runs.

What does Diastra do with your threshold?

Diastra reads every workout your Apple Watch saved in Apple Health. It finds your max heart rate from your own workouts, a guided test or a number you type, and it says which one it used. Your Easy, Threshold and VO₂max bands are drawn from that max. On a threshold run the watch holds you in your Threshold band with a tap when you drift out, and only the minutes that held are credited. Over the weeks Diastra shows whether your training is working with one of three answers. Getting fitter. Holding steady. Slipping.

The next part of this series covers threshold runs, from tempo runs to the Norwegian double-threshold method.