Dear Coach: What is Lactate Threshold?

Understanding what lactate threshold is—and how to find yours—is an important part of training and performance.

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Figuring out what your lactate threshold is is an important part of getting your training right, so that you can be sure you’re working at the right intensity for the right amount of time. But before we dive into why you should care what your lactate threshold is, let’s first take a look at what it is and how to determine it.

What is lactate threshold?

Lactate, also known as lactic acid, is a substance produced by your muscles during exercise. Specifically, lactate is produced by the muscles when they use glucose (sugar) as fuel during exercise. (Sometimes lactate is described as the waste product of glucose utilization, but technically it’s a by-product.) The more glucose used by your muscles as fuel, the more lactate they produce. You with me so far?

Okay, good. Now we have to get a little more specific about your muscle cells. Your muscles are made up of both slow-twitch and fast-twitch fibers. Slow-twitch fibers are the primary muscle fibers used during lower-intensity effort levels, and they don’t produce a lot of lactate because they don’t use a lot of glucose for fuel (they rely more on fat). Fast-twitch fibers are the primary muscle fibers used during higher-intensity effort levels, and they produce a lot of lactate because they require a lot of glucose for fuel. Still with me? Cool. Let’s move on.

How it works

Picture yourself starting a workout at an easy effort level: you’re primarily using slow-twitch muscle fibers and you’re not producing a lot of lactate. Then, you increase your effort level to moderate: you’re now using a combination of slow-twitch and fast-twitch muscle fibers and you’re producing more lactate than you were at the easy effort level. Finally, you increase your effort level to hard: you’re primarily using fast-twitch muscle fibers and you’re producing a lot of lactate.

If you think of this progression from easy to moderate to hard as a continuous range rather than three distinct effort levels, your lactate threshold is the point at which you go from producing a little more lactate because you’re working a little harder, to producing a lot more lactate because you’re working a little harder. Got it? Great.

How do you determine your lactate threshold?

So, now we need to find out what your lactate threshold is. To measure lactate concentration in your blood at varying levels of exercise intensity, you typically need to go to an exercise physiology lab. This is scientifically precise, but expensive and also not necessarily available where you live. The good news, though, is that what you really care about is the associated pace, power, and/or heart-rate at your lactate threshold, because those are the metrics you use and monitor in training, and you do have the ability to measure those things yourself.

You can do a pretty good job of determining your threshold pace (run), power (bike), and/or heart-rate (run and bike) by performing a 30-minute all-out effort, after a proper 20-minute warm-up. Your average pace/power for the 30 minutes and your average heart-rate for the final 20 minutes are your thresholds. (Some also use a 20-minute test, where your threshold pace/power/heart-rate is 95% of your 20-minute average.) This works well because 20 to 30 minutes is short enough that you can work really hard, but not so short that you can tolerate the extreme lactate build-up that occurs above your threshold. It’s right at that tipping point—right at your threshold.

Why should you care?

Knowing your lactate threshold pace/power/heart rate is great for dinner conversation (not), but what’s really helpful are the training zones that are determined based on those numbers. Improving in triathlon is all about training smarter, and by knowing your training zones, defining your training accordingly, and then adhering to those zones in execution you raise the level of quality of your training. Additionally, your training zones can improve your ability to set appropriate and metric-focused race execution targets—and who doesn’t like to PR?

RELATED: Fitter & Faster Podcast: Everything Triathletes Need to Know About Training Zones

Alison Freeman is a co-founder of NYX Endurance, a female-owned coaching group based in Boulder, Colorado, and San Diego, California. She is also a USAT Level II-certified and Ironman University-certified coach as well as a multiple iron-distance finisher.