Cortisol is an adrenal steroid hormone that helps to protect the body from the effects of stress and also is the primary anti-inflammatory hormone in the body. We often hear about athletes who have cortisol injected into injured joints. Doing so almost immediately reduces localized inflammation and pain. However, this is a band-aid approach because the cortisol does nothing to aid the healing of the injury that caused the pain. Indeed, in some cases cortisol can make the situation worse for two reasons. One is that cortisol, by masking pain can lead to placing too much stress on the already injured area, which would make it worse. Second, improperly administered injected cortisol can weaken connective tissue and thus delay healing. From a bodybuilding and fitness perspective, cortisol has engendered a bad reputation because if its characterization as a "catabolic hormone." What this means is that high levels of cortisol tend to promote the breakdown of amino acids in muscle, leading to a loss of muscle mass, a catabolic or breakdown effect. This is in contrast to anabolic hormones, such as testosterone, growth hormone, and insulin, which all work to promote muscular growth or an anabolic effect. Indeed, one of the lesser known ways that anabolic steroid drugs work is by interfering with the actions of cortisol in muscle tissue. The steroids actually block receptors for cortisol in muscle and thus prevent the catabolic effects of cortisol. While the primary anabolic effect of anabolic steroids is to increase muscle protein synthesis, this doesn't last forever and eventually with continued usage, the drugs aren't as effective in this regard. However, as long as you continue to use anabolic steroid drugs, the cortisol-blocking effect continues.
This blunting of cortisol in muscle is the primary reason why those who use anabolic steroids can train with a greater training volume and frequency, yet still make or maintain muscle gains. I used to point this out when I wrote for bodybuilding magazines and described a particular bodybuilder's routine, which often involved a large number of sets and reps. They could get away with such a larger volume of exercise because the anabolic drugs they used, such as anabolic steroids and growth hormone, limited the negative effects of cortisol in their muscles. So-called "natural" or drug-free bodybuilders don't have such advantages, and the effects of gross overtraining are far more apparent in them. One study showed that natural bodybuilders who strictly dieted and lost substantial amounts of body fat while preparing for a bodybuilding contest also showed a nearly 80% decline in their testosterone levels at the time of their contest appearances. What would happen there is a gross imbalance between the anabolic hormone testosterone and the catabolic hormone, cortisol. This, in turn, would lead to considerably smaller muscle mass and definition. One way around this problem for natural bodybuilders is to increase their carbohydrate intake as the contest . . .