Aerobics May Lower Male Hormones
Oct. 25, 1998
WASHINGTON (AP) _ Men who do a lot of endurance exercise have less male sex hormone than other men.
That's not an insult. In fact, it may indicate good news.
Researchers have found that men who do a lot of running have lower levels of testosterone even when they are not running.
But they warn that low levels of testosterone can be a sign of overtraining.
``Testosterone levels of the endurance-trained men were found to be 60-85 percent of the levels of matched untrained men,'' said researcher Anthony C. Hackney of the University of North Carolina, Chapel Hill.
Hackney's updated summary of research on the relationship of testosterone and aerobic exercise was posted on Sportscience, the Web site of the Royal Society of New Zealand, a scientific organization that is prominent for its focus on sports medicine.
Little is known about what happens to men whose testosterone levels apparently are driven down by exercise, the review article said. But so far, it appears that a little less may do some good, the article said.
For one thing, some researchers have found a heart-protecting benefit from lower testosterone levels. The report said German scientists have shown that lowering testosterone levels chemically increases production of high-density lipoproteins. HDL is the so-called ``good'' cholesterol that's said to protect coronary arteries from fatty deposits that can lead to clogging _ and thus to heart attack.
However, there is a possible sexual downside, the study noted. A handful of studies indicate that men who do high levels of aerobic exercise also produce fewer sperm cells.
And some researchers think that endurance-trained men have a lower sex drive, Hackney's report said. But there are too few cases to be sure of this _ and there is no proof that lower sex drive resulted from lower testosterone levels, it said.
Testosterone is a key hormonal trigger for muscle growth; it's one of the reasons that men can grow larger muscles than women can. However, even in endurance-trained athletes, increase in muscle mass doesn't seem to be diminished, the review said.
Why testosterone levels fall with regular, intense endurance exercise is still a mystery. It may be partly that muscles absorb more testosterone in response to exercise, and it may be that blood flow to the testes shrinks, reducing testosterone secretion by those organs, the article said. Also, exercise may interfere with activities of other hormones that stimulate testosterone production, it said.
The research also is vague on how long it takes to develop a testosterone shortfall, but some studies have found it develops after one to six months of intensive training, the article said.
Testosterone levels rise and fall normally during the day, but a workout also can affect them, and in differing ways, the review said. Men who exercise at less than full capacity can find their testosterone levels rise, even if they work out for up to 90 minutes, it said. On the other hand, moderate to hard exercise performed until the exerciser can do no more can drive down levels, it said.
The drop in testosterone among the truly hardworking athlete could be a theoretical indication that he's working too hard. Testosterone levels are lower among overtrained athletes, commented Dr. Thomas Schwenk of the University of Michigan.
The normal variability in testosterone levels makes it difficult to use the hormone as a marker for overtraining, Schwenk said. However, it can be measured fairly reliably first thing in the morning, said researcher Richard B. Kreider of the University of Memphis.
The trouble is that testosterone levels can't be counted on as a sign of overtraining because some athletes can overtrain without affecting the hormone levels, said Kreider, director of the Tennessee university's exercise and sport nutrition lab.
Athletes who are looking for signs of overtraining need also to check such things as their mood, Kreider said. If they constantly feel fatigued, and don't feel like training or competing, they may be overtrained or headed that way, he said.