Well, this discussion is clearing things right up.
Can someone contrast and compare LT to AT? What’s the diff? What’s the import of the diff to training?
Does anyone have a link to an article in a reputable journal?
Clear as mud, eh?
Lactate Threshold – A direct, invasive measurement of actual blood lactate concentrations. Involves taking blood and analyzing it periodically during an increasing power test. The classic definition is the power level at which the concentration first moves above “baseline” by 1 mmol. Some texts use a pegged number of 2.5 mmol (“milli-mole”) instead. As long as the same definition is used across trials in any given study or application, it seems to make no material difference to the validity of the study. Regardless of what you might read in Tri magazines or on Mark Allen’s website, LT can only be precisely measured with blood testing.
LT is best stated as a power level (or pace for runners): “My LT is 175 watts”, “My LT is 7:00 per mile,” etc.
In real life, LT power is roughly a maxed-out 3 to 3.5 hour effort on a bike. Frankly, LT power is lower than most coaches and training gurus would have you believe. Fit half IM athletes can sit on LT for the bike. In an IM, most everybody has to sit below LT; elites will exceed it for stretches.
Aerobic Threshold – Another testing method (first researched intensively in Germany, I think), wherein the observer does not take blood, but rather takes HR and breathing measurements. In the classic application, at some point as the power is raised, HR goes from rising steadily to rising faster or even exponentially. That “inflection point” is defined as AT. AT will sometimes correspond to LT, but not always. Due to its imprecision, it is virtually never used in a serious study.
In real life, people define AT all over the place. I personally like Gordo Byrn’s method of simply becoming aware of your breathing; when you first begin to breathe more deeply, that’s about the low end of your AT (which he calls “AeT” to be more clear in his writings).
One other acronym: Anaerobic Threshold. Well, this is the messy one, because there simply is no consistent definition or way of measuring it. Again, contrary to what Tri magazine articles and Mark Allen say, the aerobic system doesn’t magically “switch over” to the anaerobic system at some point. Both are working, in varying proportions, all the time. There is no threshold that is crossed.
I once worked out with a wise coach who shrugged when I asked about Anaerobic Threshold. He just said, “It’s that effort level where you know you’d better slow down right away or your day is over.” A physiologist might say this is somewhere near VO2max, or Maximal Aerobic Power – but I think that, in general, Anaerobic Threshold is a messy and pointless concept for the vast majority of our training efforts. But, since its acronym is “AT”, it gets confused with the other “AT”.
As for the difference to your training – not a lot. To find your benchmark for a long, steady effort, read Gordo Byrn’s “Four Pillars” articles on his website. That’s what he calls AeT; it is inherently close to LT (although a bit lower, IMO). Use that HR range as your anchor point for a mix of workouts below, at and above AeT.
This stuff is perhaps best found in a textbook, rather than a journal article. But, I don’t know of a good textbook reference.