In and out

It's hard not to laugh a bit when reminded “remember to breathe” by a trainer or other advice-giver when exercising. However, breathing is important for obvious and non-obvious reasons, and doing it right takes most people some practice.

Ignoring the obvious reasons why breathing matters, here's an explanation of the non-obvious. With the exception of anaerobic exercise, like weightlifting or any other activity that lasts less than about a minute, physical exertion requires oxygen, and the amount of power you generate is nearly directly proportional to how much oxygen your body absorbs and uses.

There's nothing magical about this. At the cellular level, most calories (energy) you burn come from sugar molecules. These molecules are held together by bonds that release the energy when broken. Your body breaks down such a molecule by using a fixed amount of oxygen. X calories, Y units of oxygen; 2X calories, 2Y units of oxygen. Thus, the number of calories expended when exercising aerobically (or not exercising at all, since being idle is an aerobic activity) is limited by how much oxygen your body can absorb and use. No breathing equals no energy consumption equals no power.

In case this isn't clear, I'll restate another way: no matter your level of fitness, whether you're a beginner or elite athlete, the amount of energy you consume is limited by how much oxygen you absorb and use. It stands to reason, then, that you don't want your upper bound to be set by something you have conscious control over, like breathing. Rather, you want the upper bound to be set by something you don't have conscious control over, like how fast your heart pumps oxygen-rich blood to the muscles.

You see, there are many potential bottlenecks in delivering oxygen to those sugar-burning muscle cells. Firstly, there's how much oxygen you're inhaling. After the oxygen is in the lungs and is available for absorption into the blood, there are several other possible limiters: (1) how much oxygen is absorbed per unit volume of blood, (2) how fast the blood is circulated through the body, and (3) how efficiently the muscles absorb oxygen from the blood. Fit persons' bottleneck is nearly always some combination of the first two: the efficiency of the cardiovascular system. (This is why professional endurance athletes such as cyclists are tempted to take drugs that boost the carrying capacity of the blood (e.g., EPO and blood doping) and/or drugs that stimulate the heart into pumping faster and harder.) However, unfit persons' bottleneck may be the third reason: the efficiency of the muscles absorbing oxygen. Though, it turns out that, on average, the muscles are capable of improving their efficiency by two- or three-fold, whereas the maximum efficiency improvement of the cardiovascular system is around one-fourth or one-half for most people. In other words, if you're unfit and your muscles can maximally absorb 1 unit of oxygen per unit time, then by becoming fit your muscles will maximally absorb 2 or 3 units of oxygen per unit time; your cardiovascular system will increase its capacity only from 1 unit to 1.25 to 1.5 units. It turns out that usually after a few months of training, the muscles will have grown past the capacity of the cardiovascular system and are no longer the bottleneck. This should make some sense with personal observation; unfit persons' muscles often feel sore after doing aerobic activities like running or swimming, but after a few months they stop feeling sore.^*

This all may sound like a lot, but there's not much to it, conceptually. Once you're past the first few months of training, your performance is limited by how much blood you can deliver to your muscles. In this light, aerobic exercise can be abstracted and generalized to this: the process of making yourself become sufficiently out of breath and then remaining in that state for an extended duration. That's how you increase the capacity of your cardiovascular system. There's pretty much no way around this; if you're not at least a little out of breath, you're simply not training hard enough. Furthermore, the more fit you become, the more out of breath you should be and the longer you should be out of breath. Of course, what you gain by your improved fitness is power—i.e., speed.

So remember to breathe. Drop that jaw, open that mouth wide, and breathe big and deep and fast. The route from the starting line to the finish line is full of energy-unlocking oxygen, so use it up.

[*] I think this has to do with how unfit persons' muscles recruit anaerobic processes to generate a significant percentage of power, even when the activity being performed is typical an aerobic one, like running. Furthermore, a fit person who is trained for a single activity limited to specific muscle groups, such as how cycling is mainly limited to the lower body, may find his muscles wholly unfit when switching to a different activity that uses different muscles groups, such as swimming and the use of the upper body. I think this is why fitness in one activity does not always translate to fitness in another activity and is a strong argument in favor of cross-training.