What is your preferred method of testing anaerobic threshold?

This is the weekly selection from our private training community: Oliver asked for feedback on threshold testing. Here is part of that discussion.

I have been getting frustrated using aerobic threshold and thought I was just doing something wrong/not reading the data correctly...

Yes, aerobic threshold can be confusing. It is the most important threshold, but there's too much kung-fu interpretation and explanation that goes on. For my own training, I would prioritize it, but for coaching, I would use anaerobic threshold. You can get 90% of the way there using some simpler rules of thumb.

What is your preferred method of testing anaerobic threshold?

I prefer using a ~4 mM lactate test on a calibrated treadmill at a sport-specific incline, but that comes with some important caveats:

1. Know that ~4 mM is only a proxy for anaerobic threshold. It's not worth pinning it down precisely, ~4 mM will be close enough, and you can test it with less fatigue than a field or lab test;
2. The treadmill needs to be calibrated to get accurate data because most brands' treadmill accuracy is horrible. The one brand I would trust is a Woodway (but they're crazy expensive;)
3. The treadmill test will give you a pace and heart rate for AnT. Use the pace as the benchmark for constant-grade training (i.e. treadmill, flat road, etc). Use the heart rate as the benchmark for variable terrain; and
4. For road runners, I would test with a 1-2% incline (depending on the pace) to compensate for the lack of wind resistance. For mountain athletes, use a 20-25% incline depending on the event they're training for. For skimo, 25%.

My second choice is the Uphill Athlete 30-minute test or the 30-minute Friel field test. (The tests are virtually the same.) In order to not force the pace, a field test should be done alone and not on a treadmill. Social pressure will force the pace, and it's too easy to do the same thing on a treadmill.