A study in the journal Clinical Endocrinology (51:687-91; 2000) examined testosterone levels in male runners, ages 55 to 65. The men ran an average of 40 miles per week, and they were matched against men of the same age who didn’t run but were otherwise healthy. The runners showed an average 25 percent higher testosterone levels than their sedentary counterparts. They also showed growth hormone levels that were four times higher than the nonrunners.
Both testosterone and growth hormone levels decline with age. That leads to several negative effects on body composition, including decreased muscle and increased bodyfat. Lower testosterone levels are also linked to greater visceral fat deposits in the abdominal area, which are associated with an increased risk of diabetes and cardiovascular disease. A relative lack of optimal testosterone levels can also lead to decreased sex drive and possible erectile dysfunction. That alone could be responsible for the frequent depression seen in men with lower testosterone levels.
While this study of middle-aged and older men showed an elevation of testosterone from regular aerobic exercise, other studies have shown that weight training is vastly superior to aerobic exercise in terms of maintaining anabolic hormones, such as testosterone and growth hormone. The key factor appears to involve intense training while avoiding overtraining. Excessive exercise of any type leads to increased cortisol release. Cortisol, an adrenal stress hormone, has an inverse relationship with testosterone and GH levels: As cortisol rises, the anabolic hormones decline.
Other means suggested to maintain testosterone levels in conjunction with a proper level of exercise include consuming at least 20 percent of calories as fat. Anything below that tends to decrease testosterone levels. Lack of sufficient sleep is also known to depress testosterone levels by as much as 40 percent. The amount of sleep needed, however, varies with individuals. Finally, lifting heavier weights (a subjective matter) coupled with less rest between sets is also associated with higher testosterone levels following training. IM