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Men, Women and Speed. 2 Words: Got Testosterone?


New York Times- Health

BEIJING — No matter what happens in the men’s marathon here Sunday, one thing is all but certain. The winner will run the 26.2-mile course faster than the winner of the women’s marathon last Sunday.

The woman who won, Constantina Tomescu of Romania, was fast, of course, finishing the race in 2 hours 26 minutes 44 seconds — more than a minute ahead of the second-place finisher. But for a variety of intrinsic biological reasons, the best women can never run as fast as the best men, exercise researchers say.

Women are slower than men in running, in swimming, in cycling. Whether it is a 100-meter race on the track or a marathon, a 200-meter butterfly swim or a 10-kilometer marathon swim, the pattern holds

And even though some scientists once predicted that women would eventually close the gender gap in elite performances — it was proposed that all they needed was more experience, better training and stronger coaching — that idea is now largely discredited, at least for Olympic events. Researchers say there is no one physiological reason for the gap, although there is a common biological thread.

“To a large extent, it’s a matter of testosterone,” said Dr. Benjamin Levine, director of the Institute for Exercise and Environmental Medicine at Presbyterian Hospital and the University of Texas Southwestern Medical Center in Dallas. “That’s why systematic doping of women is even more effective than systematic doping of men. That’s why the East German women were so much more successful than the East German men.”

The hormone affects everything from muscle size and strength to the size of the heart to the amount of oxygen-carrying blood cells in the body to the percentage of fat on an athlete’s body. Every one of those effects gives men a performance advantage.

Testosterone, Levine said, gives men what he calls a bigger and better-fueled engine. Their skeletal muscles, which do the work during exercise, are bigger. And their hearts, which provide fuel for the work, are bigger, too.

It is not that every man is inherently better than every woman.

“A very lean, well-trained woman will be faster than a less lean, less fit man,” he said. But that is not the issue in the Olympics, where the men and women are among the world’s best.
Even when scientists correct for the fact that men are bigger than women — and bigger animals or humans have bigger hearts — men’s hearts are still larger than the hearts of women. Exercise makes hearts grow, but male hearts grow more than female hearts, Levine has found.
He recently conducted a study that recruited sedentary men and women and trained them to run a marathon. At the start of the study, Levine said, the men’s hearts and the women’s hearts were the same size relative to the size of their bodies.

“Gram for gram, they had the same size hearts,” he said. “We trained them for over a year. Heartbeat for heartbeat, they had the same training.”

And the result? “The women’s hearts did not grow anywhere near as big as the men’s hearts,” Levine said.

Another factor comes into play. Because men have more testosterone, they have less fat and more muscle than women

“That’s extra weight women have to carry,” said Hirofumi Tanaka, an exercise researcher at the University of Texas. It inevitably takes its toll, slowing women down.
Even the leanest women, like elite marathon runners, have a body fat measurement that is around 8 percent, compared with 4 percent for elite male marathoners.
“Unless women are doping and fundamentally changing their biology, they are left with body fat percentages that may be twice as much as men’s,” Levine said.
Female athletes and their coaches are well aware of the performance penalty that extra fat confers.

“Coaches tell them that if they want to be successful, they have to be leaner,” Levine said. “It’s a constant struggle for female athletes who are in sports where being lean is a determinant of success.”

But fat, researchers said, is only part of the explanation. “Even if you take body fat into account, women are still slower,” Tanaka said.

Another hindrance to women is their lower red blood cell counts; their hemoglobin levels tend to be 10 to 15 percent lower than those of men. The more red cells, the more oxygen-carrying hemoglobin is in the blood. And the more hemoglobin, the more oxygen getting to exercising muscles.

Women lose blood when they menstruate, but they also do not make as many red blood cells. Testosterone increases red blood cell production, said Dr. Mark Tarnopolsky, an exercise researcher at McMaster University in Ontario.

Yet red blood cell levels, too, are only a piece of the gender-gap puzzle. In the past, Tanaka said, researchers have removed blood from male runners to give them hemoglobin levels like those of women. The men were slower, but they still ran faster than women.

Testosterone also changes the makeup of muscles. Women, with their lower testosterone levels, end up with a smaller proportion of Type 2 muscle fibers, which are used to generate speed and power and strength, Tarnopolsky said. And, he said, he and his colleagues have found that women’s muscles are less efficient in storing and using glycogen, a carbohydrate that is the main fuel used in distance events.

“It’s the absolute ability to store and use carbohydrate that determines your speed,” Tarnopolsky said.

Nonetheless, researchers expect women’s performances to improve with time and with experience. No one thinks women — or men, for that matter — have reached a performance ceiling.

But, Levine notes, training, talent and a competitive drive can take women only so far.
“There are some biological factors that cannot be overcome,” Levine said.