What Is the Lactate Threshold?
What Is the Lactate Threshold?

The fitness world is full of weird terminology that might make working out and getting in shape seem impossibly difficult. Just take “lactate threshold,” for example. Though it might sound like the spot where the milkman leaves his bottles, the lactate threshold is actually something you’ll likely encounter if you’re a regular exerciser. It can also be an effective indicator of your fitness level and something you can (and probably should) strive to improve.


What Is the Lactate Threshold?

Very simply, it’s the intensity at which exercise goes from sustainable to unsustainable. But if you want to get scientific, it’s the exercise intensity at which your body must switch from primarily aerobic (oxygen-dependent) energy production to primarily anaerobic (oxygen-independent) energy production. The switch causes a rapid spike in lactate levels as your body tries (unsuccessfully) to deal with an exponential rise in another byproduct of this energy production: hydrogen ions.

“That buildup of ions causes ‘muscle acidification,’ which you’ve likely felt as a deep burning sensation,” says Trevor Thieme, C.S.C.S., Openfit’s senior manager of fitness and nutrition content. ” It typically occurs when your heart rate reaches 80 to 85 percent of its maximum.”


So…what does that mean?

Let’s say you’re out on a run. You’re feeling good, so you push the pace. Naturally, your heart rate climbs. You still feel good, so you push it harder, and your heart rate increases even more, until you reach a point when your lungs are burning and your legs feel like they’re on fire. Keep going at that intensity and you might even feel a little woozy.

You’ve just blasted through your lactate threshold: that level of effort at which exercise goes from “tough, but bearable” to “Lord, make it stop.”


Lactate vs. Lactic Acid

Before we go on, let’s clear up a widespread misconception.

Upon reading about lactate and burning muscles, many people might jump to the conclusion: This is lactic acid we’re talking about, right?


Lactic acid a substance found in sour milk. It’s NOT produced during exercise, and it almost never builds up in the body.

Lactateon the other hand, is an entirely different substance. It’s found not just in working muscles, but in every cell in your body, at all times. Lactate is not a waste product that needs to be cleared from the system, and lactate itself actually doesn’t make your muscles sore.

“In truth, lactate threshold is a bit of a misnomer because lactate isn’t the problem,” says Thieme, adding that it’s the surplus of the previously mentioned hydrogen ions that causes the discomfort. “But, hydrogen ion accumulation threshold is a bit of a mouthful.”

One more time:

  • Lactate is a fuel and ion buffering agent, and it’s beneficial for you.
  • Lactic acid is a substance found in sour milk, not in working muscles (or anywhere else in the body for that matter).

Say it over and over to yourself until you believe it. (Still confused? More on all of this here).


The Aerobic and Anaerobic Systems, and the Lactate Threshold

All of this sciencey talk can sound way more confusing than it actually is. Here’s another way to look at how your body deals with challenging physical tasks, and why your muscles start burning when they do.

Consider a diner that employs two short-order cooks, Erin and Annie. When things are slow, Erin’s on duty: she’s smooth, efficient, and keeps the kitchen clean. When the diner gets busy, though, Erin can’t keep up, so the bulk of the work shifts to Annie. Annie’s super fast, but she stresses the kitchen staff and tires out fast.

Erin is your body’s aerobic system: she’s best for everyday tasks like eating, walking, working at a desk, and, if you’re in decent shape, easy jogging and other forms of light exercise. The aerobic system runs mostly on carbs (in the form of glucose) and fat, which it converts to energy with the help of oxygen. This process is clean and efficient, but slow. That’s why the aerobic system can only keep up with easy to moderate physical activity.

Annie is your body’s anaerobic system: she steps in when you to crank up the intensity—a sprint, a bike ride up Dead Man’s Hill, a 50-yard all-out swim—and need energy fast. The anaerobic system runs mostly on carbs. Oxygen never enters the picture.

Now…stay with us here. Turning glucose and glycogen into energy produces hydrogen ions and pyruvate. When those two things combine, you get lactate, which helps to regulate metabolism, power the nervous system, and maintain long-term memory. All of that is good!

But things take a turn for the worse when your body starts producing more hydrogen ions than can be combined with pyruvate. That tipping point is the lactate threshold, and it’s why most people can walk comfortably for hours, but can only sprint for a few minutes — walking doesn’t cause H+ levels to skyrocket like sprinting does. As the ions accumulate, your muscles become more acidic, contraction becomes more difficult, and you begin to feel that deep burn that’s so familiar to regular exercisers.


Can You Improve Your Lactate Threshold?

Since your lactate threshold corresponds to the most intense exercise you can handle before you hit the proverbial wall, it’s a fair measure of your overall fitness. And since you can improve your overall fitness levels, that should mean you can also increase your lactate threshold level. The question is: How?

“Exercising at or near your lactate threshold by doing sprint intervals, HIIT, and other high intensity activities can help you not only increase your threshold, but also function longer once you reach it,” Thieme says. “But in order to do that, you first have to know what your lactate threshold is.”


Lactate Threshold Test

To determine your lactate threshold, choose your preferred a form of steady-state exercise (running, cycling, rowing, etc.), strap on a heart rate monitor, and warm up for about 10 minutes. Then perform your chosen activity at the fastest pace you can maintain for 30 minutes without stopping. Your average heart rate for the final 20 minutes is your “lactate threshold heart rate,” or LTHR.



Like other technical fitness terms, such as periodization or plyometrics, lactate threshold sounds confusing, daunting, and only vaguely relevant to people pursuing general fitness. But in essence, it measures how intensely you can exercise before fatigue starts taking a toll on your performance. And the higher your lactate threshold is, the fitter and faster you’ll be. “The bottom line is that you can increase your capacity for high intensity effort,” says Thieme, “and who doesn’t want that?”