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Posted: November 20, 2004
Science of Sport: Lydiard Makes Me Hit the Books
The Running Research News Weekly Training Update
The great coach, Arthur Lydiard, is visiting the United States right now (his speaking tour ends on December 14), and his American sojourns always force me into the library.
The treks to the stacks are not a way of avoiding Arthur, who is a wonderful fellow, but are simply the result of Arthur's fondness for the use of the term "Aerobic Threshold," or AT (which I sometimes call "Arthur's Threshold").
In a letter to the Michigan Runner, Arthur once wrote "Performance can be improved only by raising the aerobic threshold," and also - reinforcing his point - "Aerobic threshold is the governing factor in performance levels in endurance events" (reference provided upon request).
That made aerobic threshold sound kind of important to me, but I'll have to admit I was puzzled by Arthur's statements and by his long-term attraction to AT. I have been a keen student of physiology since that fateful day in 1973 when, after the Dean of the College of Arts & Sciences at the University of Rhode Island told me that yes, I would have to declare a major before proceeding further with my education, the word "Zoology" suddenly and inexplicably slipped out of my mouth. Forms were signed, "add" cards were filled out, and a rigorous undergraduate program of physiology, anatomy, and embryology quickly was undertaken, followed by graduate studies and research of a physiological nature. Not once, however, was AT mentioned in any of my classes (in contrast, its sister - anaerobic threshold - was discussed more times than I care to remember), and - today - AT almost never makes an appearance on the pages of the top-of-the-line exercise-physiology texts or the in-the-know physiological journals. In short, I didn't learn about Arthur's Threshold during my formative years, and I don't hear about it during my current career as a running journalist. As a result, each Lydiard stop-over baffles me momentarily - and sends me scurrying for the shelves (you might think that I would remember the concept from one visitation to the next, but - alas - my long-term memory is not a strong point).
On the current Lydiard excursion, I took the bold step of putting together a Google search for AT, hoping to spare the crush of 25,000 undergraduates and yet one more trip across the Red Cedar to the MSU reference centers. On page one of my Google results, I found an extraordinary definition of Aerobic Threshold as the "point at which anaerobic energy pathways start to operate" (please see http://www.brianmac.demon.co.uk/endurance.htm).
Such an AT demarcation is certainly easily understandable to most runners. For many runners, it makes sense to think that there might be some point, some decent running velocity, at which aerobic processes just can't provide all of the energy which is needed to move along at that pace, causing anaerobic energy creation to "kick in" and provide a little lift.
The truth, however, is that the definition is farcical. If this statement about AT were true, it would mean that AT is the running pace you utilize during the very first step of your workouts. Your first step, after all, is the point at which anaerobic energy pathways begin their operations. There are several reasons for this, but - keeping things simple - we can say that no aerobic energy creation can take place without a little anaerobic energy generation happening first. When your muscles break down glucose for the energy you need to run, they first break the little fellow down to pyruvate, yielding some energy for muscle contractions in a process which is purely anaerobic (without oxygen). The pyruvate can then be metabolized aerobically to provide lots more fuel for your exertions, but the anaerobic part has to come first. In addition, the first step of your workout is actually fueled by the molecules of ATP which are already in your muscles; they use their high-energy phosphates to trigger muscle contraction in a process which is also entirely anaerobic.
I realized I needed to hit the stacks! But, I have to mention that the definition cited above was also packaged with the information that AT occurs at about 75 percent of maximal heart rate - and that it takes place at a ticker rate which is around 20 beats per minute lower than the one associated with anaerobic threshold. Interesting - but ridiculous!
My late-night raid of GV201.R4 reminded me that the notion of AT was actually first fully developed (in a scientific way) in 1980 by some fellows named James Skinner and Thomas McLellan at the University of Western Ontario (please see ref. # 1). Here's how Skinner and McLellan framed AT: If you start running at a very slow tempo but gradually and progressively increase your pace, until you finally reach a point at which your speed is so high that you can no longer continue (Skinner and McLellan envisioned this process as being gradual enough so that it would take about 25 minutes or so), lots of interesting things happen to you from a physiological standpoint, as follows:
(1) As your speed increases, your rate of oxygen consumption increases in a linear way (that is, the plot of oxygen-consumption rate as a function of speed is a straight line).
(2) As your speed increases, your heart rate increases in a linear way, too.
(3) As your speed increases, your ventilation rate (the amount of air passing in and out of your lungs each minute), increases in a linear way up to a certain speed. At that "certain speed," ventilation rate continues its linear increase, but with a steeper slope (the increase in ventilation per unit increase in speed is greater than before).
(4) As your speed increases, your rate of carbon-dioxide production increases in a linear way up to a specific speed, too. At that specific speed, it continues its linear increase, but with a steeper slope (similar to what happens with ventilation rate).
As Skinner and McLellan noted, these "break points" for both ventilation rate and carbon-dioxide production occur at about the same running speed, which for an individual runner is usually at an intensity of about 40 to 60 percent of VO2max (55 to 72 percent of maximal heart rate). They called this simultaneous break point (the speed at which both ventilation rate and carbon-dioxide-production rate begin a steeper rise in relation to running velocity) the Aerobic Threshold.
The Aerobic Threshold is not the point at which anaerobic processes begin to operate, as many have envisioned it (remember that anaerobic processes begin during the first stride of any run), but what is it? What is actually happening when ventilation rate and carbon-dioxide production turn north?
No one is absolutely certain, partly because the underlying processes are so varied and complex. Skinner and McLellean simply noted that the Aerobic Threshold had little to do with anaerobic processes and was probably related to changes in muscle-recruitment patterns and "an imbalance between the rate of pyruvate production and pyruvate oxidation." They were trying to get at the idea that extra pyruvate within the muscle cells might be converted to lactic acid, which could release hydrogen ions, which could step up breathing rate and carbon-dioxide production.
Perhaps we should not worry too much about what AT actually represents, however. After all, isn't Arthur's Threshold still tightly connected with endurance-performance capacity, as Arthur has said, no matter what is actually going on when it occurs?
In truth, the supportive evidence (for AT) is not very strong. Some studies have shown that AT fails to move upward at all in response to regular endurance training, and only a few investigations have linked upgraded ATs with improved performances. Most importantly, a careful search of the scientific literature since 1966 uncovers no evidence that AT is a good predictor of endurance performance (any sleuths who find otherwise - please contact me). In other words, if you lined up 100 similarly trained athletes according to their ATs, from highest to lowest, and then lined up the same group according to their 10-K times, from fastest to slowest, the lines would look quite different. In contrast, other variables such as maximal running speed, velocity at VO2max, and lactate-threshold speed have been found to be excellent predictors of endurance-performance capability in a variety of investigations.
So what's wrong with AT? It doesn't contain very much information for one thing, merely reflecting the running speed at which carbon-dioxide production and ventilation rate take off a little bit. In many cases, it is not even tightly linked with VO2max (and thus does not even reflect total aerobic capacity). Factors such as velocity at VO2max, maximal running speed, and lactate-threshold velocity, on the other hand, possess lots of info and can be used in a predictive way. A runner with a high velocity at VO2max, for example, automatically possesses great economy, a high max-oxygen-consumption rate, and often a high max running speed, too; AT tells us nothing about these critically important variables. A runner with a terrific maximal running speed has the right neuromuscular characteristics (expressed via explosive footstrikes coupled with long stride lengths) to be an excellent endurance performer, provided the underlying physiology is set; AT tells us nothing about these factors, either.
The bottom lines? There are four things which you need to be concerned about as a competitive endurance runner: (1) Velocity at VO2max, which can be improved optimally by training at your velocity at VO2max, (2) Lactate-threshold speed, which can be upgraded optimally by carrying out scalding sessions above your lactate-threshold intensity, (3) Max running speed, which can be bolstered by improving your running-specific strength and explosiveness, and (4) Running economy, which can be enhanced with strength training, hill sessions, and lots of running at goal paces. AT just doesn't make the list, and there is really no reason why it should.
Hate mail may be sent to firstname.lastname@example.org. Many thanks for joining me again this week; your interest is very greatly appreciated.
Very kindest regards,
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