It is now clearly established that testosterone and anabolic steroid supplementation increase muscle mass and maximal voluntary muscle strength (105-108). Early studies suggested equivocal effects of anabolic steroid use on athletic or exercise performance (105). However, it is important to recognize that because of ethical reasons, most of those sanctioned studies did not administer anabolic steroids at the high dosages used by athletes. This prompted researchers to report no effects, whereas anecdotal reports by individual users touted large, substantial effects. Those anecdotal reports were tainted by their lack of scientific control for confounding factors, such as extent of training and "the placebo effect." Nonetheless, the findings in those "nonexperimental" studies suggested body mass gains of 10 or 20 kg, as well as up to a 30% increase in muscle strength (106). Several well-controlled short-term studies have found smaller, but significant, increases in body mass, lean body mass, muscular strength, and concurrent reductions in fat mass (105,106).
Anabolic steroid usage is not limited to "weight-lifting-power" athletes. Endurance athletes (e.g., distance runners and triathletes) have also used anabolic steroids. However, most studies have failed to demonstrate a substantial, beneficial effect of anabolic steroids on maximal oxygen consumption (i.e., key determinate to aerobic-endurance capacity) (103-105). It has been proposed that endurance athletes who use anabolic steroids choose to do so because they recover from exercise training bouts more rapidly. This idea seems logical, because performing more exercise training is a major stimulus to improve the cardiovascular-respiratory system and, thereby, aerobic performance, and androgen treatment should negate the decline in testosterone that normally follows heavy exercise.
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