Aerobic and anaerobic are two terms that we find in frequent use in the health and fitness arena; but regrettably, they are sometimes used erroneously, or perhaps they are used in a way that does not truly enhance their training effects. The latter may even be a result of the former.
My purpose here is to dispel just a couple of the most common inaccuracies, following which I shall move on to a very simple and yet accurate way to explain what it is to exercise aerobically and anaerobically.
I believe it was my freshman year of high school when I was informed that aerobic exercise entails that done with oxygen, while anaerobic is that done without oxygen. The instructor, bless his heart, was no doubt attempting to avoid a complicated explanation. However, even the very statement itself, that aerobic exercise is with oxygen while anaerobic is without, is fatally flawed. We require oxygen to simply exist, yes?
At still other points, mostly in my adult life, there have been those who categorize any form of rhythmic movement or exercise besides strength training as aerobic exercise. In effect, these individuals are using the terms cardiovascular and aerobic interchangeably.
You may have your own anecdotes, perhaps including statements made by fitness professionals, of misuse of these terms. I would submit, however, that for the sake of the education we undertake and for our class participants in the Spinning® program, we must get these terms clearly defined and use them well.
Here, then, is as simple as I may offer: we require energy that may be expended (or burned) in order to exist (and certainly to move). Our bodies mobilize two primary fuels during rest and exercise: fat (actually fatty acids) and carbohydrate (blood glucose). The aerobic energy pathway favors the more efficient, longer term fuel source: fat. The anaerobic pathway (relying on carbohydrate) is more easily available in the short term, but carbyhydrate is present in much lesser quantities than fat, which means that anaerobic exercise typically leads to relatively rapid fatigue. Essentially, then, movements primarily done by large, thick muscles are too fast and powerful in nature to be done for any true endurance. Movements done, in contrast, largely by thinner and lengthier fibers favor slower speeds and/or less force applied, which allows for these movments to be done for endurance, or aerobically. The last detail is this: rarely to never are our energy systems functioning on a purely aerobic or anaerobic basis, which means our bodies actually expend fat and carbohydrate simultaneously! The major consideration is the same, though: the more toward the anaerobic or carbohydrate-based energy pathway we commit ourselves, the more rapidly fatigue will ensue.
Of course, what may be said regarding aerobic and anaerobic movement can be quite complex, and so the above delineation is far from complete; however, sometimes we find of benefit to create clear distinctions and move toward the more complex as we may.