Lactate Threshold Explained: A Beginner's Guide for Runners

Lactate threshold is the hardest effort you can keep up before lactate starts building up in your blood faster than your body can clear it. For most runners it sits at roughly the pace you could race for about an hour, which is why coaches use it to set tempo and threshold sessions.

It sounds like lab talk, but you do not need a blood test to use it. Here is what is happening in your body, how to estimate your own threshold, and how to train it without overdoing it.

What is lactate threshold, in plain words?

When you run, your muscles break down carbohydrate for energy, and lactate is made along the way. At an easy pace your body clears and reuses lactate as fast as it is made, so the level in your blood barely moves. As you speed up, production rises. At some point it rises faster than your body can clear it, and lactate starts to pile up. That turning point is your lactate threshold.

Picture a bath with the plug out. The tap is lactate being made and the plughole is your body clearing it. Turn the tap up a little and the water level stays steady. Turn it past a certain point and the bath starts to fill. Run just under threshold and you can hold the effort for a long time. Run well above it and fatigue builds quickly, so you usually have to slow down within minutes.

Does lactic acid make your muscles sore?

No, and it is one of the most common running myths. Lactate is not a waste product that sits in your legs for days. Your body uses it as fuel, and blood lactate levels usually fall back to normal within an hour or so of a hard session. The soreness you feel a day or two later, often called DOMS, is generally linked to unfamiliar or downhill work, such as your first hilly run in months or a new strength move.

The burning feeling during a hard rep is real, but it is generally thought to come from other changes inside the working muscle rather than lactate itself.

Is there more than one threshold?

Yes, and this is where the jargon gets messy. Sports scientists often talk about two turning points. The first, sometimes called LT1 or the aerobic threshold, is where lactate first starts to rise above resting levels. It marks roughly the top of your easy, chatty running. The second, LT2, is where lactate starts to climb steeply. When runners and coaches say threshold, they nearly always mean this second one, and so does this guide.

You may see lab figures of around 2 and 4 millimoles per litre linked to these two points. Treat them as rough averages, not fixed rules. The real values vary from person to person, and different coaches, labs and watch brands use slightly different definitions.

Why does lactate threshold matter for runners?

Your VO2 max is the most oxygen your body can use, a bit like the size of your engine. Our guide to VO2 max explained for beginners covers it in full. Lactate threshold is about how much of that engine you can use for a long time before things fall apart. Two runners with similar VO2 max scores can race very differently, because one can work closer to their ceiling before lactate piles up.

Research suggests endurance performance comes down to a few things working together, mainly VO2 max, threshold and running economy (how efficiently you move). Many coaches focus on threshold because it tends to respond well to steady, consistent training. A higher threshold means your everyday pace feels easier, and you can hold a quicker pace for longer in a 10K, a half marathon or the running sections of a hybrid race.

How does lactate threshold relate to tempo and threshold runs?

Threshold runs are designed to sit at or just under your lactate threshold, usually broken into reps with short jogs in between. Tempo runs usually sit a touch slower, as one longer continuous block. Both help nudge your threshold upwards. We break down the details in tempo run vs threshold run: what is the difference.

In feel, threshold effort is often described as comfortably hard. Your breathing is deep and steady, you can say a few words at a time but not hold a conversation, and you could keep going for a while but would not want to. On a 1 to 10 effort scale, most runners put it at around 7 to 8.

How can you estimate your threshold pace or heart rate?

A lab test with small blood samples taken on a treadmill is the most precise option, but most runners do not need one. These simpler methods get you close enough to train with.

The 30-minute test is linked to US coach Joe Friel. Warm up for 10 to 15 minutes, then run for 30 minutes as hard as you can hold evenly, ideally on a flat route with no stops. Press lap at 10 minutes and use your average heart rate from the final 20 minutes as your threshold heart rate. Do it alone rather than in a race or a group, as company tends to push the numbers up. Your average pace for the full 30 minutes is a rough guide to your threshold pace.

Whichever method you choose, treat the number as a starting point. Fatigue, heat, sleep and hills all move it on the day, and many coaches suggest re-checking every 6 to 8 weeks rather than every week. If you want to set the rest of your training zones around it, our guide to running heart rate zones walks through all five.

What does a threshold session look like?

Every session starts with 10 to 15 minutes of easy running and finishes with 10 minutes easy. The main set sits in the middle. Here is a simple four-week starter block for runners who already run around three times a week.

A good threshold session ends with you feeling you could have done one more rep. If your last rep is much slower than your first, or you finish gasping, you ran too fast. On hilly routes, hot days or after a poor night's sleep, run by effort or heart rate instead of pace.

How often should beginners do threshold runs?

For most beginners, one threshold or tempo session a week is plenty, once you have a few weeks of regular easy running behind you. The rest of your running should be easy. A common guide is that around 80% of your running is easy and the remaining 20% is harder work.

If you train hybrid, remember that HIIT and heavy leg days tire you out too. A balanced week might look like this:

• Monday: full-body strength
• Tuesday: threshold run
• Wednesday: rest or mobility
• Thursday: easy run plus upper-body strength
• Friday: HIIT session
• Saturday: rest or a short easy run
• Sunday: long easy run

Try not to put a threshold run the day after a heavy leg session or a hard HIIT class, and keep at least one easier day between hard days.

What are the most common threshold mistakes?

• Running reps at race pace. Threshold is hard but controlled, never all out.
• Doing it too often. Two or three hard runs a week on top of HIIT and strength adds up fast.
• Chasing a pace on a bad day. Heat, hills and tiredness all change it. Run to feel.
• Skipping easy runs. Easy running builds the base that helps lift your threshold too.

How does Edge fit threshold training into your week?

Edge is a free fitness app, and Edge Pro builds a fully personalised plan across running, strength, HIIT and mobility, ready within 24 hours. Your threshold runs sit in the same plan as your gym and HIIT sessions, so hard days can be planned around each other rather than stacked. Not sure where your threshold pace sits? You can message a real coach anytime and ask. Edge syncs with Strava, Garmin, Apple Health and Coros, and Edge Pro starts with a free 7-day trial.

This article is general guidance, not medical advice. If you are new to exercise, returning from injury, pregnant, or managing a health condition, speak to your GP before starting, and see a physio for any niggle that does not settle.