Lactate Threshold

Lactate Threshold Definition

What is lactate threshold?

Lactate Threshold is simply the exact exertion level that, past which, causes the lactate levels in your blood to accumulate much faster than your body can clear them. This generally means that your body is working harder than it clear and you'll begin to feel fatigue build up quickly.

What does lactate threshold mean on a running watch?

Most modern running watches show you an estimate of your lactate threshold by relating it to a pace and heart-rate as a proxy for how hard you're working.

The idea being, that beyond the shown pace and heart-rate (your lactate threshold), you'll begin to accumulate lactate in your system faster than you can clear it.

Is my running watch's lactate threshold estimate accurate?

It's impossible to say how accurate your watch is for you personally, but always remember it is just an estimate. Your actual lactate threshold requires blood samples during hard work, which your watch can't do.

Your watch can only estimate this using your heart rate and pace as a proxy for effort level. So depending on how your watch translates those figures in it's formula, it can either be very accurate or very inaccurate.

Regardless how close your watch is to the real figures though, you can use your watch's estimate as a guide. If it improves over time, it's safe to say you're improving your lactate threshold. Watch the trends, not the actual figures.

What is lactate / lactic acid?

Lactic acid is a normal acid byproduct released by your muscles as they work. The harder your muscles work, the more they produce.

At easy paces it's cleared faster than it's produced.

Beyond your lactate threshold however, it builds up quicker than it's cleared. This is the acid that causes most of that burning type feeling you feel in your muscles when working hard.

When running, there is always a low level of lactate in your blood, it's a normal byproduct of muscles doing their job. At easy paces, this lactate is easily removed from your system. Most lactate you produce is actually recycled back into usable energy for your muscles and a small fraction is sent to be excreted through urine.

The problem with this recycling process, is that it's slow. At easy paces, you produce a small enough amount of lactate that it's ok and your body can easily recycle the lactate as you produce it. This means at slow paces, lactic acid should never really be a limiting factor.

Once you begin to work harder however, and the amount of lactate you produce increases, you start to build accumulate lactate faster than these recycling processes can keep up with.

The exact effort level (normally show by pace and heart-rate on modern watches) that your body produces more lactate than you can clear, is your lactate threshold.

How do I calculate my lactate threshold?

The golden standard, most accurate way is through a test in lab or with lactate blood pricks that measure lactate levels as your run.

Most people don't have mobile labs though, so there are a few ways we can get a good idea.

• Online Lactate Threshold Calculators - Estimates from a recent race normally.
• 30 Minute field test - run hard for 30 minutes after a good warm up, and use the average heart-rate and pace from the latter 20 minutes of the effort as your lactate threshold. Pace yourself evenly, it should be really hard towards the end.
• Use your watch's estimate - a helpful guide.

For full details, read my full guide to calculating your running lactate threshold.

How long can you run beyond your lactate threshold?

Most guidelines indicate that at an effort beyond your lactate threshold for around an hour. In theory, if you're able to run at your exact lactate threshold though, you could run much longer.