Bodybuilders live and die by their testosterone levels. Numerous studies by Shalender Bhasin and colleagues found that muscle mass and the capacity for muscle hypertrophy is directly proportional to blood testosterone levels. Testosterone also promotes aggressiveness and competitiveness, which are vital for any athlete. Bodybuilders seek to maximize muscle mass and minimize fat. This is a difficult task, because the body uses muscle proteins as fuel during periods of caloric restriction.
Research from Finland showed that blood testosterone levels decreased markedly in elite wrestlers who lost weight rapidly in two to three weeks. The athletes lost 8 percent of body-weight, 16 percent of fat mass and 8 percent of fat-free mass (includes muscle) during the study through caloric restriction, increased exercise and dehydration. Testosterone and luteinizing hormone decreased by 63 percent and 54 percent. The changes in these hormone levels were highly related to weight loss. The study showed that rapid weight loss associated with weight-class sports could have profound effects on metabolism, body composition and hormone status, which might negatively affect health and maturation in growing athletes.