I recently commented on a VeloNews article regarding the use of oxygen deficit as it relates to interval training. The article was so fraught with error, or deception, that I wanted to set the record straight on the topic. My goal by the end of this post is help everyone realize that more often than not many of these articles are poorly disguised attempts to sell you on a product, service, training method.
There are only 3 Energy Systems
Starting from the top, this one debunks many of the misconceptions and claims made about training zones. One reason why I like Greg McMillan’s take on Zones, is because they really do represent a quality that we wish to train, not really a quantity we can measure. Sure, zones are helpful in prescribing training and quantifying training stress, but these are just abstract ways to quantify a quality; this is actually the heart of social science (I say pseudo science sometimes) where we take someones statement and give it a score. When considered in context it is useful, but not really literal. In either case, the use of zones assumes two things mainly:
- each is distinct and measurable
- time is certain zones is better than other zones
The latter gets to the heart of threshold or sweetspot (an attempt to rebrand the former without any basis in reality), because time here is no more beneficial than any other area. In fact, research using high-intensity interval training (HIT) shows without a doubt that intensity above threshold and activation of high-threshold (ie, fast twitch) motor units yields better results; 30 sec sprints seem as effective as 4 min intervals at improving 40 k TT performance (Stepto, MSSE 1999).
Another important fact is that at no time is one single energy system producing all the energy. Time and intensity are a key driving force of ATP demand and production and that ATP is provided by either:
- Stored ATP and Creatine Phosphate (CP) – ~10 sec for each. CP is at the heart of why creatine monohydrate works as a supplement for REPEATED sprints. ATP is the ultimate energy source and CP helps deliver a third phosphate back to ADP to make make ATP which is then used again. Suffice it to say, you can’t really store extra ATP, but you can store a lot of CP. Also, ATP/CP are replenished during recovery using the AEROBIC system. Think of ATP as a wad of cash in your wallet; easy to spend and short lived.
- Glycolytic system produces rapid ATP and lactate ~30-90 sec. As you hopefully know by now, lactate is not the bad by-product its been made out to be, its basically an intermediate system to produce ATP rapidly, as well as be converted to ATP itself elsewhere in the body (beyond this article). Research indicates that lactate is not only useful, but that high lactate levels may yield greater returns on endurance training. Think of this system like a credit card; quick an easy purchases that need to be paid back in the future.
- Aerobic system produces the most ATP, but is slow in doing so. This means that to use this system you have to go much slower than the other two, but training allows you to really boost this system a lot. Despite what some website authors would like you to think, though, most of the energy derived during even maximal exercise of 2 min or longer comes from the aerobic system. Think of the aerobic system like an investment account, accruing interest; you’ve got a lot in savings to draw from, but it takes a lot more time and red tape to get all that money.
As I said earlier, all these systems function together to respond to duration and intensity during exercise. To get a better idea of how responsive the aerobic system is, though, I’ve provided a nice Figure 1, below:
It’s obvious from this classic depiction that by 90 sec more than 75% of ATP are supplied aerobically. So then, when an author tries to use flawed physiological reasoning to sell some type of training, I get highly annoyed. The idea that you need to warm-up hours on end to fully realize training benefits is flat wrong. Moreover, the (incorrect) use of Levi Leipheimer’s training to make this case is a logical fallacy; never mind the confirmation bias, we’re drawing conclusions from a training paradigm that has nothing to do with oxygen deficit. We’re made to believe the claims are true because the author uses an authoritative figure (a PhD) to make this case that is in fact based on a misrepresentation of facts. Why am I certain he’s incorrect? Review Figure 2, below:
O2 deficit (incorrectly labeled above as O2 debt) is essentially the ATP produced during exercise that could not be provided by the aerobic system. At the early stage of exercise the deficit is high based on system activation (Figure 1), while exercise at or near VO2 max can occur for similar reasons, though not for long. Incidentally, this latter point is one argument Tim Noakes has used against VO2 Max as we conceive it; in brief, how can max be max if we can exercise above max? The historical belief was that this deficit led to a (oxygen) debt that needed to be “paid” back after exercise, as was evidenced by athletes gasping for air even after short events. However, this concept has largely been refuted and the term Exercise Post Oxygen Consumption (EPOC) has replaced it. EPOC is the elevated O2 consumption (VO2) and energy expenditure after exercise, popularly called “after burn”.
The fact is, we need to supply muscles with energy and this may require using all systems maximally. However, at no time does the O2 deficit impact training outcomes; physiologically speaking, the VeloNews article is absurd nonsense. It’s clear that VO2 during submax training, like threshold, reaches a stable level within 2-3 minutes, so why is the your first interval junk then? Technically, you can run out your door and just start training without a warm-up (you’ll feel terrible), but its still training. Maybe if you train an hour you’ll burn marginally more fat, but it would be inconsequential. Finally, the author claims that the O2 deficit explains why sprint training requires a long warm-up and rest because your aerobic system is solely responsible for your recovery of ATP. Fatigue, however, is complex and not fully understood, and extends well beyond merely replacing ATP; I think the author must have skipped his lectures on neuromuscular fatigue.
I hope this article was informative and again highlighted the need for skepticism even from so called experts. Always ask yourself what the author has to gain by the article, then don’t be afraid to do a little research on your own. If it sounds too good to be true, or espouses one method as best, it is likely a deception. I believe George Brooks*, one of the leading exercise physiologists of our era and an expert in O2 deficit, summarizes this topic best:
“Measuring O2 deficit or debt may have a purpose in contemporary research, but measuring O2 debt after exercise is inadequate for estimating anaerobic metabolism during exercise.” Brooks, Fahey, & Baldwin; Exercise Physiology, 2005.