Testosterone, the male sex hormone that determines secondary sex characteristics in men, is important to capacity and endurance when exercising. As men age, they gradually lose testosterone in a process called andropause, which is somewhat similar to menopause among women. By age 70, as many as 40 to 50 percent of men have low testosterone levels (Anawalt 2001). Symptoms of andropause include the loss of bone and muscle mass, depression, loss of sexual function, and heart disease. At the same time testosterone is declining, growth hormone levels are dropping (Karakelides 2005).
While it might seem that testosterone and growth hormone supplementation would enhance exercise, study results have been conflicting and incomplete. A few small-scale studies have shown it is possible to temporarily boost growth hormone levels by taking supplements that naturally increase growth hormone and testosterone levels; however, there is not yet enough data to recommend hormone replacement in the context of increased exercise endurance and capacity (Anawalt 2001). Considering that some cancers are hormone dependent, testosterone supplementation should be approached with caution by aging men who want to boost their exercise capacity and endurance. Hormone replacement therapy should be done only under the supervision of a qualified physician and after comprehensive blood testing.