24.6–24.10

Hormones influence nearly every facet of an organism.

Growth hormones influence stature.

Figure 24-15Unsporting conduct. Many athletes have tested positive for illegal testosterone supplementation.

The Tour de France is one of the world’s most grueling tests of strength and endurance. The annual bike race occurs over three weeks, as riders cover more than 2,200 miles (3,500 km), in 21 separate stages. In 2006, an American rider named Floyd Landis, in 11th place overall, turned in a performance in stage 17 that was so improbably fast that some commentators called it “the greatest performance ever.” His win brought him within 30 seconds of the overall lead and propelled him, over the final four stages, to the Tour de France victory.

But Landis’s glory was not to last. Less than a week after his victory, it was announced that he had tested positive for unusually high levels of testosterone, which a second test confirmed. The typical ratio of testosterone relative to the hormone epitestosterone in men is 1:1 or 2:1. While the Tour de France allows ratios of up to 4:1, Landis’s level was 11:1. Moreover, the lab tests detected a synthetic form of testosterone in his bloodstream, in addition to the naturally produced hormone. Landis was stripped of his title and banned from the sport for two years.

Scandal has continued to surround the bicycling world, perhaps peaking in 2012 when Lance Armstrong, despite his denials, was also found to have used illegal performance-enhancing drugs over a long period of time. Later admitting to the drug-use charges, he was stripped of his seven Tour de France titles and banned from competition for life (FIGURE 24-15).

While the revelations that competitors resorted to illegal supplementation in an effort to boost physical performance have been disappointing, the history of sports is littered with drug scandals, frequently involving testosterone or its variants. Olympic gold medalist Ben Johnson, for example, was stripped of his medal and the world record for the 100-meter sprint in 1988 when he tested positive for a synthetic steroid hormone similar to testosterone. In 2003, 104 Major League Baseball players (of 750 in the league) tested positive for illegal performance-enhancing drugs, and in 2005, 111 professional football players did. And the scandals are not limited to men. Track-and-field athlete Marion Jones won five Olympic gold medals in 2000, only to have all of them taken away when she admitted that she had illegally taken performance-enhancing drugs, including a muscle-building “designer steroid” called tetrahydrogestrinone, or “the clear.”

Testosterone and many structurally similar steroid hormones affect the composition of the body. Experimental studies of testosterone supplementation in men reported weight gains of 5–12.5 pounds within 10 weeks. The gains were due primarily to increases in lean muscle mass in the shoulders, upper chest, and upper arms, areas with the highest concentrations of testosterone receptors. In randomized, controlled studies, researchers also documented strength increases of 5% to 20% in both experienced and novice athletes.

Figure 24-16The normal effects of testosterone in the body, and the harmful effects of testosterone supplementation.

Testosterone has also been shown to influence locomotor performance—speed and endurance, in particular—in animals. In an experimental study on lizards (the northern fence lizard, Sceloporus undulatus), two to three weeks of supplemental testosterone caused a 24% increase in sprinting speed and a 17% increase in stamina.

Such testosterone supplementation causes changes in physique and physical performance by activating processes that lead to increased muscle mass. Produced primarily by the testes in males (but also by the adrenal glands of both males and females), testosterone binds to receptors in target cells, then moves to the nucleus and influences gene expression (see Figure 24-5). The cells increase their protein synthesis and grow, resulting—in the case of muscle cells—in increased muscle mass (and simultaneously reducing the rate of production of fat-storage cells). Supplemental testosterone also increases cell division among satellite cells, small cells found in muscle tissue that aid in muscle repair. Additional responses to testosterone supplementation include the development of secondary sex characteristics, including chest and facial hair and a deepened voice—effects seen in both males and females.

There are numerous adverse effects to supplemental steroid hormones. They include increased blood pressure and risk of heart disease, damage to the kidneys and the liver (where the steroids are metabolized), development of breast tissue in males, and atrophy (shrinkage) of the testes as negative feedback leads to reduced production of testosterone in response to the increased levels of circulating testosterone (FIGURE 24-16). Also, because testosterone increases cell division—increasing muscle mass, for example—it increases the risk of unrestrained cell division in many tissues and, consequently, increases the risk of many types of cancer.