Aerobic training remains a point of contention for those engaged in bodybuilding and fitness activities. While the superiority of aerobics for helping to reduce excess body fat is clear, other issues arise that make many people reluctant to include any type of direct aerobic training in their fitness or bodybuilding regimes. One such issue is the notion that if you include aerobics in your training, you will lose muscle mass. I recall professional bodybuilder Vince Taylor once told me that he never did any type of aerobics in his training because it caused him to rapidly lose muscle mass. And there is some scientific basis to this contention. Concurrent training, or including both resistance training and aerobics in one workout, may compromise strength and muscle gains according to one school of thought. The reason offered for this interference of gains is because doing aerobics following a weight workout initiates changes in muscle or more specific adaptations, that favor muscular endurance over muscle protein synthesis. And since muscle protein synthesis is the cornerstone of increased muscular hypertrophy, the implications are clear.
Confounding the issue, however, are other studies that not only show no blunting of muscle gains with aerobic exercise but in some cases increased muscular growth. This is especially true for older people who are out of shape and begin a weight-training and aerobic program. Such people show changes in muscle tissue indicative of increased muscular hypertrophy, such as more activation of satellite cells, muscle stem cells heavily involved in the repair and muscular hypertrophy process. As such, the issue of aerobic interference with training remains controversial. From my experience of observing thousands of people at every level training over the years, I think that whether aerobics will interfere with resistance-induced muscle gains depends on a number of factors. Among these is how much body fat you have and whether you are thin or obese. Thinner people have a bit more problem with aerobics because they are at greater risk of burning up muscle protein, which would slow muscle gains. The other risk involves those who overdo aerobics in an effort to speed body fat losses. I recall one elite professional bodybuilder who did four hours of aerobics daily to lose body fat. When he started this, he was out of shape and nearly obese. But within three months, he was shredded, ripped to the bone, as bodybuilders like to say. But he had a lot of fat to burn, and he also used anabolic steroids, which not only helped to spare muscle tissue but also tended to speed fat loss because the drugs increase sensitivity to catecholamines, such as epinephrine and norepinephrine, which promote the release of stored fat in fat cells.
Back in the "Golden age of Bodybuilding," which many refer to bodybuilding in the 70s when Arnold was the king of bodybuilders, no one did aerobics except endurance athletes. Indeed, there was no aerobic equipment at all . . .