I wasn't able to reply directly to the "sticky" post about the 2 x 20 AT test.

The author of that post wrote:
"The higher the percentage of maximum heart rate you can sustain for the duration of the test, the fitter you are. This translates into being able to cycle faster for a longer duration."

The AT should really be Lactate Threshold since AT is not as accurate a description of what the threshold is and measures.

The percentage of MHR a person sustains at their AT/LT is mostly genetic, and is only slightly influenced by the level of fitness unless you're comparing a completely untrained person with that same person when they have trained. Once a person reaches a relatively moderate level of aerobic fitness the HR at AT/LT will not change during the year by more than a few bpm even if they get fit enough to be National Champion.

Some untrained people, or slightly trained people will have an AT/LT that is 90% of their MHR, while another person who might be very fit will find their AT/LT HR to be near 80-85% of their MHR. It is genetic. This is one of the reasons MHR is a relatively poor guide for aerobic and anaerobic training.

You want to improve your performance (watts, speed, distance, etc.) at AT/LT, not your HR at AT/LT.

"Keep in mind, you are looking for ONE NUMBER.... not a RANGE OF NUMBERS... Often, I'll run through the first 20 minutes with my students, then when I talk to them in the 5 minute break, they say something like, "oh, I was between 156- 160". Aaaaaaaugh!!!!!!!!!! You are looking for that one number, not a range. So if it's 160, it's ONLY 160... not a range of different numbers that's "around" 160."

I don't think you're being fair to your students. A few bpm will make virtually no difference in the training benefit they'll derive. They can aim at 160 or 157 or 162 and the training effect will be about the same.

Lab tests will show that the HR near LT will in fact vary by 0-5 bpm depending on the accuracy of the measurement device, hydration status, level of glycogen stores both prior to, and during the testing, environmental conditions like heat and humidity, etc. And if you're repeating a 20 minute test (two 20 minute tests) to determine the AT/LT then these factors and possibly cardiac drift, level of fitness, and motivation will influence the results. Adrenaline alone can change the HR during the test by at least a few bpm.

If a person performed these tests a week apart it's quite possible their HR number would be different by a few beats because of these factors. Not a problem.

Sally's book was good for its time (10-15 years ago), but much has been learned since then about AT/LT testing and training. I don't think you'll find many (good) cycling coaches these days using % of MHR as a guide for training intensities. % of AT/LTHR or % of power at LT is much more common and more accurate/appropriate.


P.S. I've been lab-tested many times at one of the best labs in the US, by one of the foremost experts in the world of cycling physiology.