Aerobics, you either love it or hate it. For some bodybuilders, aerobic training forms the core of their fat-loss program, especially when preparing for contests. Such training often varies, with some doing about 20 minutes, twice a week, while others do two aerobic sessions a day, for 45 minutes duration of each session. Many Internet sites warn about the "catabolic effects" of doing excessive aerobic training. But the salient question here is: when does aerobic exercise become excessive? If you look at the question from a hormonal point of view, it would seem that bad effects begin at about the 60-minute mark. At that point, cortisol levels begin to significantly elevate. Cortisol is an adrenal corticosteroid hormone that, among other effects, can markedly induce muscle catabolic effects. It does this in tandem with myostatin, a protein that inhibits muscle growth. Cortisol promotes the release of myostatin. But an often overlooked feature of cortisol is that it helps to mobilize fat for use as an energy source. As such, it would appear that the rise in cortisol that occurs with longer exercise sessions occurs more to help promote fat use than for purposes of muscle breakdown. In fact, ingesting a source of branched-chain amino acids prior to doing aerobics blocks the catabolic effects of cortisol on muscle.
Still, common sense would decree that more exercise uses more calories, and as such should lead to greater fat loss. What isn't considered in this equation is that the greater the use of energy, the more of a compensation effect that occurs afterward. For reasons that are still hotly debated among scientists, the body seems to sense when a large amount of energy has been used up and then sets into play automatic processes that result in increased appetite as a means to compensate for those lost calories. Writer Gary Taubes often talks about this effect. He actually says that exercise is ineffective as a weight-loss tool because of the calorie compensation effect that occurs after exercise. The fact that countless people have lost significant amounts of body fat from a combination of diet and exercise doesn't seem to faze Taubes. Instead, he points to the 97% recidivism rate for most dieters. That is, nearly everyone who loses appreciable amounts of fat nearly always gains it back. But a closer look at such people reveals that those likely to gain back the lost weight are those who opted to diet strictly, but do little or no exercise. Just the opposite of what Taubes contends.
Although many will have you believe that losing excess body fat is merely a matter of ingesting fewer calories than you burn, it's a bit more complex than that because of several intervening factors. For example, there are hormones in the body that control the sense of hunger, and if these are upgraded, it would take a supreme amount of willpower to keep lost . . .