[Scott Johnston]

Great question.  The short answer as to why I didn’t question Judd’s (whose opinion I respect) assertion that you can find AeT in a VO2max test with a rapid ramp-up/short stages is that I don’t know how that could be done.  In hindsight, I should have asked him to explain how he does that.   All can do is explain my experience of looking at hundreds of these tests.

The long answer follows:

I’m not a physiologist, but my supposition is that when the ramp rate is too fast, especially in the low-intensity aerobic zones, the aerobic metabolism is playing catch up, and its response to the change in intensity has a significant time delay.  If that is true, the aerobic metabolism does not reach an equilibrium state, which takes several minutes.  If that is true, then the gas exchange data in the form of RER, the respiratory exchange ratio, while accurately reflecting the metabolism, will not give the same information as it would when the stages are long enough for metabolic equilibrium to occur. This is why METs (Metabolic Efficiency Tests) have 3-4-minute stages.   Ask the lab how long the test stages are.

Another BIG problem I often see in lab tests is the very short warm-up time before they start the test and start collecting data.  As I have explained, the aerobic metabolism is slow to get cranked up to full capacity and slow to respond to changes in intensity (remember, the aerobic metabolic pathway’s job is to provide energy for long duration steady state work.  The anaerobic path’s job is to respond to rapid changes in work rates).  So if the work rate increases suddenly, like going from near zero (driving to the lab and walking in) to even light exercise, the aerobic metabolism needs time to get firing on all cylinders.  If that happens, there is a very good chance, even with 3-minute stages, that the first few stages will have a lagging metabolic response.  I just evaluated a test like that yesterday for one of our coached athletes.  So a long, very easy warm-up of at least 10 minutes will give better results. But many labs don’t do that. Maybe it is because they want to get their customers in and out quickly so they can get on to the next one.

So, that’s my argument against using a short-stage gas exchange test for determining AeT.   I have seen this in so many tests, some with stages as short as 15 seconds.  What the center argument would be, I can’t imagine.  Maybe I need to get Judd back on to explain that.

As for the AnT, that is an entirely different argument.  The whole point of identifying the AnT is to determine the intensity that you can sustain for many minutes (like 30-60).  If that is the point, then why not just do a real test of maximum sustainable effort?  I call this kind of test a performance test. Since what we ultimately care about is improving our performance out in the field, we should use a performance test when possible.  The Gas Exchange Test is a proxy test, not a performance test.  Performance tests are like time trials.  The AnT test is simply going as hard as you can for 30+ minutes and seeing what your average HR is.  The AeT test measures HR drift during an hour of low-intensity exercise.  I also like to do AeT and AnT time trials on the same piece of terrain every couple of months to see if your training is improving your performance.  These tests are free, and you can take them whenever they fit into your schedule. They provide a true measure of performance.

If your performance is improving, you can’t be too far off the mark with your training.

I hope this helps.

Scott