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The direct definition of lactate threshold (the point when the lactate concentration spikes above the body's capacity to remove it) isn't very useful without a measuring device. Instead, the lactate threshold pace is often described as the pace that can be maintained during 1 hour of steady max effort. I saw many remarks that the LT pace falls between the HM race pace and the 10k race pace.

Meanwhile, the most popular field test to obtain the lactate threshold is Friel's test (also known as the 30-minute test) which instructs to run 30 min at steady max effort and take the last 20 min avg as the lactate threshold pace (or LTHR). The result obtained with Friel's test is often described as an accurate approximation of the real LT.

How is it possible that the pace from the 30-minute test at max steady effort is a good estimation of the LT pace which is the pace at max steady effort for 1 hour?

For example, if I get a pace of 5:00/km from the 30-min test, then I can't run at this speed any longer or it would not be max effort. Definitely not twice as long. By this reasoning, the true pace at LT must be a slower pace than the result of Friel's test, probably a lot slower.

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It's a little bit of an interpretation problem, that Friel addresses in one of his blog posts.

Near the top of this page is a definition of lactate threshold:

So, in short, your lactate threshold is defined as the fastest pace you can run without generating more lactic acid than your body can utilize and reconvert back into energy. This pace usually corresponds to 10 mile or half marathon race pace.

So, your LT is your max effort for a 10 mile race. This max effort will be slower than a 30 minute max effort. If you could run 7 minute miles for 10 miles, that's about 1:10. You in theory should be able to run a faster pace for 30 minutes.

If you're having a hard time picturing that, think of max effort for a 5k vs max effort for a 400m.

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    Thanks John, but distance vs. duration interpretation is not my issue. I reread your answer a few times and I only see that you state the problem again. As you say, if my LT pace is at max effort for 10 miles (e.g. 70 min), then I can run 30 minutes at max effort with a faster pace. There is no way anyone can do max effort for 70 minutes at the same pace as max effort for 30 minutes. We know it and use this faster pace as an LT pace estimate anyway (and call it accurate).
    – oskarryn
    Oct 17, 2023 at 17:34

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