Lactate Threshold 101: The Basics

imageHate it or love it, you’re almost certain to be familiar with that burning sensation in your legs during a hard effort. The “running through molten peanut butter” feeling that plagues the homestretch of races and workouts. The sharp stab of exhaustion that makes even one more step feel nearly impossible.

Endurance athletes spend a lot of training time looking for that sweet spot just before they cross into the dreaded burn zone. If you haven’t heard of it before, welcome to the wonderful world of  training at Lactate Threshold! In this post, we’ll take a very basic look at what Lactate Threshold (LT) is and why it matters to ALL runners, not just elites or competitive racers. In a later piece, we’ll show you 3 ways to find your very own Lactate Threshold and give you tips on how to get the most out of LT training.

Ready? Set? Let’s go!

***Disclaimer: I’m still new to Lactate Threshold training. If you’re a coach or an expert, you’ll be able to tell that I am NEITHER of those things. Feel free to chime in and comment if you’re knowledgeable on LT and find mistakes in my own understanding of all this. I’m always up for learning more!

Ball-and-stick model of L -lactic acid
A sciency look at the stuff that makes going out too fast suck so hard. (Photo credit: Wikipedia)

Lactic Acid: Malicious or Misunderstood? 

Lactic Acid was discovered by chemists in the 18th century, and for a long time it had a pretty bad rap. Scientists thought that it was a harmful waste product in the body and, as a result, coaches advised their athletes to train at paces that kept them away from “feeling the burn” of lactic acid. Since then, however, scientists have redeemed lactic acid by determining that it’s not actually bad for us. Some of them don’t even think it’s what causes the burn! (more on that below) Some scientists have suggested that there are even benefits to having lactic acid in our bodies.

Think of lactic acid as the “exhaust” given off by contracting muscles, much like the exhaust given off by a car. Lactic acid is produced when glucose (our main source of fuel at high intensities) is metabolized. If you’re humming along efficiently on a slower run you won’t notice it. It’s still being produced, but the body uses fat as a fuel source at lower intensities and less lactic acid is produced when fat is metabolized. The body flushes it out of the tissues and uses it for other things. At moderate-to-higher intensity, however, the body switches over to breaking down carbohydrates as fuel and an increase in lactic acid production is the result. Hit the accelerator long and hard enough on a run, and the “exhaust” will start to build up.

When lactic acid is produced, both lactate ions and hydrogen ions are formed. Guess what? The science suggests that it’s more likely the hydrogen that sets off the chain reaction leading to “feeling the burn” during an intense workout.

Defining Lactate Threshold

Lactate Threshold is the intensity we can run just before lactic acid  begins to accumulate.

When lactic acid starts to build up in your muscles and “leak” into your bloodstream (we’re using that term to simplify things), you’ve officially surpassed your LT. This doesn’t mean you’re going to need to stop right away, but it won’t be long before you’ll need to slow down.

Kinda sorta there-ish. (from
Kinda sorta there-ish.

Paces faster than your LT can’t be sustained over long periods of time. According to endurance sports guru (and Racing Weight Cookbook author) Matt Fitzgerald, your LT corresponds to the fastest pace you can sustain for 30 to 60 minutes: that’s 30 minutes for less fit folks and 60 minutes for the highly fit. At the risk of sounding uber-vague, your LT is the pace that falls somewhere between super-high intensity and not-so-high intensity. Fast enough to be a challenge, but not so fast that your pace is erratic and you’re completely wiped out after the workout.

Hands down, Lactate Threshold is one of the most effective performance markers used by competitive coaches and athletes. Matt Fitzgerald explains that LT training makes us more capable of sustaining faster paces for longer periods of time. “It doesn’t make you faster,” he says, “but it does make you much slower to fatigue when running fast. Since LT intensity is in the neighborhood of 10K and half marathon race pace for most runners, we’re talking about a type of training that significantly increases how long a runner can sustain a desired race pace for such events.”

Training at LT pace is not easy, but it’s extremely valuable if you are training to race or simply to improve your endurance.

Who Cares?? 

It's worth paying attention to, I promise!
It’s worth paying attention to! Really!

If you’re currently feeling a bit overwhelmed by science-y facts ‘n figures, or if you are more of a recreational runner, you might be asking, “Why should I pay attention to all this fancy shmancy Lactate Threshold stuff? I don’t like to run fast or even race. Why does this matter??”

I think the most basic benefit of LT training is the variety it offers. Personally, I tend to lose motivation when all of my runs are the same over the course of a week. Before I started taking a closer look at the science behind my training, most of my workouts looked the same. Numbers and paces and training zones were way over my head (or so I thought…) so I just went out and ran the same courses at the same paces all the time. “Whatever feels good” was my mantra.

If that’s your thing, rock on! For me, though, “whatever feels good” got BORING. I stopped looking forward to my workouts because they were so predictable. The few times I DID try to run a bit faster, I’d hit that “peanut butter slog” at the same place/pace every single time. Even though I wasn’t technically training to get faster or race, I never really got stronger either. It was difficult to want to continue running when I couldn’t see any tangible improvements or benefits.

Adding LT workouts and goals to your weekly routine can help mix things up a bit. It can propel you to the next level of fitness. And it can give not only your legs but also your mind a new challenge, which keeps things interesting and fun….in a satisfying, sweaty, post-workout endorphin rush kind of way!

What do you think? Willing to learn more and give Lactate Threshold training a try? Already incorporating it into your routine? Not interested at all?


  • Fahey, T., PhD, Don’t “Dis” Lactic Acid, Sports Science, Vol. 36, No. 9, Muscular Development (September 1999)
  • Gladden, L., Lactate uptake by skeletal muscle. Exercise Sport Science Review 17:115-155 (1989)
  • Roecker, K., Predicting competition performance in long-distance running by means of a treadmill test. Med. Sci. Sports Exerc., Vol. 30, No. 10, pp. 1552-1557 (1998)

I'm a nomadic runner who loves moving from city to city with my husband and Great Dane. I write about training with a Type-B personality, battling bad running habits, and becoming comfortable with sub-3 marathon racing despite my race-phobia. After a soul-searching year away from running, I'm thrilled and terrified (thrillified?) to be making a major comeback in 2018!

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