ANABOLIC-ANDROGENIC STEROIDS: Mechanism of Action and Effects on Performance Thomas D. Fahey
Exercise Physiology Laboratory
California State University, Chico
Chico CA 95929 USA
Fahey, T.D. (1998). Anabolic-androgenic steroids: mechanism of action and effects on performance. In: Encyclopedia of Sports Medicine and Science, T.D.Fahey (Editor). Internet Society for Sport Science: 7 March 1998.
Anabolic steroids are drugs that resemble androgenic hormones (sometimes called male hormones) such as testosterone (Figure 1). Athletes consume them in the hope of gaining weight, strength, power, speed, endurance, and aggressiveness. They are widely used by athletes involved in such sports as track and field (mostly the throwing events), weight lifting, and American football. However, in spite of their tremendous popularity, their effectiveness is controversial. The research literature is divided on whether anabolic steroids enhance physical performance. Yet, almost all athletes who consume these substances acclaim their beneficial effects. Many athletes feel that they would not have been as successful without them.
There are several possible reasons for the large differences between experimental findings and empirical observations. An incredible mystique has arisen around these substances, providing fertile ground for the placebo effect. The use of anabolic steroids in the "real world" is considerably different from that in rigidly controlled, double-blind experiments (in a double blind study, neither the subject nor experimenter knows who is taking the drug). Most studies have not used the same drug dosage used by athletes. Institutional safeguards prohibit administration of high dosages of possibly dangerous substances to human subjects. Subjects in research experiments seldom resemble accomplished weight-trained athletes. Under these conditions, we must assess the results of sound research studies, as well as clinical and empirical field observations, in order to obtain a realistic profile of the use, effects on performance, and side effects of these substances.
How Anabolic Steroids Work
Male hormones, principally testosterone, are partially responsible for the tremendous developmental changes that occur during puberty and adolescence. Male hormones have androgenic and anabolic effects. Androgenic effects are changes in primary and secondary sexual characteristics. These include enlargement of the penis and testes, voice changes, hair growth on the face, axilla, and genital areas, and increased aggressiveness. The anabolic effects of androgens include accelerated growth of muscle, bone, and red blood cells, and enhanced neural conduction.
Anabolic steroids have been manufactured to enhance the anabolic properties (tissue building) of the androgens and minimize the androgenic (sex-linked) properties. However, no steroid has eliminated the androgenic effects because the so-called androgenic effects are really anabolic effects in sex-linked tissues. The effects of male hormones on accessory sex glands, genital hair growth, and oiliness of the skin are anabolic processes in those tissues. The steroids with the most potent anabolic effect are also those with the greatest androgenic effect.
Steroid hormones work by stimulation of receptor molecules in muscle cells, which activate specific genes to produce proteins (see Figure 1). They also affect the activation rate of enzyme systems involved in protein metabolism, thus enhancing protein synthesis and inhibiting protein degradation (called an anti-catabolic effect).
|Figure 1: How a Steroid Hormone Works|
Heavy resistance training seems to be necessary for anabolic steroids to exert any beneficial effect on physical performance. Most research studies that have demonstrated improved performance with anabolic steroids used experienced weight lifters who were capable of training with heavier weights and producing relatively greater muscle tension during exercise than novice subjects. The effectiveness of anabolic steroids is dependent upon unbound receptor sites in muscle. Intense strength training may increase the number of unbound receptor sites. This would increase the effectiveness of anabolic steroids.
Anti-Catabolic Effects Of Anabolic Steroids
Many athletes have said that anabolic steroids help them train harder and recover faster. They also said that they had difficulty making progress (or even holding onto the gains) when they were off the drugs. Anabolic steroids may have an anti-catabolic effect. This means that the drugs may prevent muscle catabolism that often accompanies intense exercise training. Presently, this hypothesis has not been fully proven.
Anabolic steroids may block the effects of hormones such as cortisol involved in tissue breakdown during and after exercise. Anabolic steroids may prevent tissue from breaking down following of an intense work-out. This would speed recovery. Cortisol and related hormones, secreted by the adrenal cortex, also has receptor sites within skeletal muscle cells. Cortisol causes protein breakdown and is secreted during exercise to enhance the use of proteins for fuel and to suppress inflammation that accompanies tissue injury.
Anabolic steroids may block the binding of cortisol to its receptor sites, which would prevent muscle breakdown and enhances recovery. While this is beneficial while the athlete is taking the drug, the effect backfires when he stops taking it. Hormonal adaptations occur in response to the abnormal amount of male hormone present in the athlete's body. Cortisol receptor sites and cortisol secretion from the adrenal cortex increase.