Testosterone is an anabolic steroid synthesized in the testes. Anabolic hormones increase muscle mass, protein synthesis, and retention of nitrogen. It is estimated that 4%-12% of adolescent males abuse steroids to improve athletic performance or appearance.48 Studies on men with low testosterone showed that testosterone supplementation combined with resistance training produced a significant increase in lean-body mass and strength compared to resistance training or testosterone alone.49 Additional studies have shown that testosterone supplementation increases strength, lean-muscle mass, and bone density as well as reducing fat mass.50 One study showed that muscle strength and power increased in a dose-dependent manner with increasing testosterone dosage. This study also demonstrated that testosterone supplementation does not improve muscle fatigability or specific tension.51
Restoring testosterone levels can improve athletic performance but should be considered only for individuals with low testosterone levels. Side effects of supra-physiologic doses of testosterone can be severe, including liver disease, low sperm counts, changes in mood and behavior, increased hematocrit levels and prostate-specific antigens, decreased high density lipoprotein cholesterol (HDL), increased low-density lipoprotein cholesterol (LDL), and adverse changes in thyroid hormones.52,53 Unfavorable cardiovascular changes can occur, such as left-ventricular hypertrophy, which remain after discontinuing testosterone supplementation.54 Androgen precursors to testosterone, such as androstenediol and androstenedione, have also been studied. A study on adult males with normal testosterone levels during high-intensity resistance training found that supplementation with these products initially increased testosterone but that these levels returned to baseline within 16 weeks. In addition, the researchers did not find improvement in muscle strength or body composition, and found that there was an increase in estrogen-related compounds and adverse changes in lipid profiles and results of cardiovascular risk assessments.55
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