Competitive bodybuilders usually have no particular fondness for aerobics but grudgingly do it to lose fat, particularly prior to a contest. That makes sense, since fat can only be burned in the presence of oxygen, and no form of exercise requires a greater oxygen intake than aerobics. Contrary to what you may read or hear, it’s just not possible to fully duplicate the effects of aerobics with weight training alone. In fact, attempting to do so defeats the whole purpose of weight training, which is based on progressive resistance.
But many bodybuilders have slipped into overtraining by becoming a bit too enthusiastic about aerobics. In their zeal to get as cut as possible, some follow the maxim that “more is better” when it comes to aerobics.
Unfortunately, the brain perceives excess aerobics as a form of stress and responds by initiating a cascade of hormonal events that results in an increased secretion of cortisol. Among its many functions, cortisol promotes a catabolic pathway, leading to muscle breakdown and loss.
When cortisol is elevated, opposing hormones, the anabolic ones, usually decline. That helps explain the often low testosterone levels seen in endurance athletes, particularly those who overtrain and don’t get enough rest.
From a bodybuilding perspective, low testosterone coupled with high cortisol is disastrous. Not only do muscles atrophy under such conditions, but the higher cortisol levels also promote fat deposition in the trunk, obscuring muscle definition. Cortisol’s promotion of water retention further blunts hard-earned muscle definition.
A new animal study points to another mechanism whereby excessive aerobics may reduce testosterone levels.1 Twelve rats were divided into exercise and control groups. Those in the exercise group swam for three hours a day, five days a week.
That regimen led to significant declines in testosterone levels, sperm manufacture and internal sex-organ mass. The researchers measured levels of chemicals known to increase under oxidative conditions and noted that they were high in the exercising rats. The high oxygen intake associated with aerobics produces more free radicals, which are by-products of oxygen metabolism.
Normally, the body’s defense mechanisms neutralize the effects of free radicals, but in this case the level of exercise overwhelmed the rats’ defenses, leading to unchecked free-radical production. Free radicals tend to attack tissues rich in polyunsaturated fats, such as cellular membranes, and compromised cell function leads to various negative health consequences, including cancer and heart disease.
In the study the excessive aerobic activity led to damage to testicular cell membranes, which are rich in polyunsaturated fats. That, in turn, decreased the activity of enzymes involved in testosterone synthesis. It also reduced blood flow to the testes, lowering testosterone output.
Some caveats are in order. First, the study involved rats, and what happened to the rats may or may not occur in humans. On the other hand, human-subject studies have shown that excessive endurance activity often does result in lower testosterone levels. Another thing to consider is what constitutes “excessive” endurance exercise. The rats in this study exercised for three hours a day. Recent studies involving human subjects show that cortisol levels rise after one hour of continuous aerobic exercise. One hour would likely be a sensible time limit for aerobics, enabling you to gain all the benefits while avoiding the possible side effects.
Research shows that the body responds to regular exercise by upgrading its free-radical defense system, including the various antioxidant enzymes produced in the body that constitute the first line of defense. Still, it would be prudent to assist the defense systems by taking antioxidant supplements and eating foods rich in natural antioxidants, such as fresh fruits and vegetables. While all antioxidants offer benefits, a nutrient called lycopene, which is found in watermelon and in such cooked red vegetables as tomatoes, is known to concentrate in the testes. In fact, studies indicate that men who consume lycopene show about a 30 percent reduced risk of prostate cancer. I suspect that lycopene may also help prevent the oxidation that leads to the lowered testosterone synthesis described in the rat-based study.
1 Manna, I., et al. (2003). Effect of intensive exercise-induced testicular gametogenic and steroidogenic disorders in mature Wistar strain rats: a correlative approach to oxidative stress. Acta Physiol Scand. 178:33-40.
©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
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