Date: 2006-01-21
Author: Mike Orr <>

The aerobic system is one of three metabolic pathways that provide energy to the muscles. SWAT Fitness has a good explanation. The muscles just take from whichever pathway has it most readily available. The aerobic system predominates most of the time; e.g., when sleeping, walking, or doing vigorous activities. That's good because it's fueled by fat and has no side effects except heavy breathing. It's called aerobic because it requires oxygen and produces carbon dioxide and water, thus the heavy breathing when the activity is vigorous. The problem is, the aerobic system can't keep up with explosive movements like weightlifting, running up a flight of stairs, or punching somebody out. That's where the other to pathways come in, ATP-PC (Phosphage) and Anaerobic Glycosis. ATP-PC is immediate -- the carb fuel is stored in the muscles themselves -- but lasts only thirty seconds before diminishing. Anaerobic glycosis is the breakdown of glycogen (from carbohydrates) without oxygen. It lasts three minutes, predominating when ATP-PC expires. But anaerobic glycosis has a byproduct, lactic acid, which irritates the nerve endings and causes the "burning" sensation that makes you want to quit. (Scientists disagree on whether it's lactic acid itself that causes the burn or the general pH imbalance in the blood, but for our purposes it doesn't matter.) So fitness can be defined as being able to tolerate/manage the burn until the aerobic system kicks in.

So "aerobic" exercises are kind of misnamed. They don't use the aerobic pathway exclusively. In fact, aerobic exercises are primarily designed to waste large amounts of energy. This both burns excess calories and forces the heart rate to go up, which makes the heart stronger. A stronger heart pumps more blood per stroke and can thus pump less often. Some believe this promotes longevity. Some people define fitness solely in terms of the heart: the lower the heart rate when doing the same amount of vigorous work, the more fit you are.

But what aerobics? Aerobics classes are about jumping around with or without little platforms. But anything that gets your heart rate up counts as aerobic exercise: calisthenics, bicycling, climbing stairs, boxing, running, swimming, doing construction work, skiing. Even weightlifting can be aerobic if you keep the rest between sets short and lift fairly rapidly. But some activities produce a higher heart rate and thus burn more calories than others. And there's a difference between general aerobic capacity and specific sports training. Any heartrate-raising activity will raise your general endurance level, but only activities similar to the particular sport movement will have the greatest impact on your sport performance. For instance, wrestlers and boxers generally run five miles or more a day. But Randy Couture says MMA fighting (UFC) is more like sprints than a marathon: it depends more on explosive movements than a continuous push. So he recommends interval training rather than steady running unless you really need to lose some fat first. You can use the "two minutes intense, two minutes slow" intervals used in boxing gyms, or count the "interval" and "hill" timings on an aerobics machine and do the same on an outdoor track.

My favorite aerobic machine is the elliptical bike. It burns more calories than the treadmill, stairmaster, rower, or bicycle, I think because you're moving both your legs and arms rapidly. Running and jump rope give a higher heart rate, but my mind wanders too easily when running and then I trip over the raised panels in the sidewalk. (You know, where there's a crack and one side is higher than the other. My toes always seem to hit the side of the higher panel in midstep. I can catch it when I'm walking, but when running it usually results in torn jeans and scraped hands when I land. And on the treadmill you hit the edge and fall off, or have to stomp really hard to prevent falling.) Bicycling is the least effective aerobic contraption, both because you're using only your legs and because the bicycle is the most efficient transportation mechanism in existence in terms of distance per calorie. Bicycling uphill, yeah. But bicycling flat, well, it beats walking. Speaking of walking, if you walk during the day to public transportation, and choose the stairs rather than the elevator, and walk to the store and library and other errands, even if you only walk ten minutes at a time, you'll burn some 300 calories over what you would with a door-to-door automobile lifestyle.