Differences in Body

Differences in body fat arise at puberty when young women begin to store fat in their stomach, buttocks, and legs. This, in addition to skeletal differences, gives women's bodies their curvy shape. Men usually carry their fat in the abdomen. Overall, women have about 10% more body fat then men, which is necessary to maintain fertility. As we discussed in Chapter 2, body fat is required for female fertility because a hormone called leptin, secreted by fat cells, tells the brain if there are enough fat stores to support a pregnancy. When a female does not have enough body fat, the hormones that regulate menstruation are blocked and menstruation ceases. Lack of menstruation can be permanent and results in sterility and bone damage. Excessive exercise or starvation that leads to the cessation of menstruation, called amenorrhea, causes permanent damage when the estrogen that normally increases prior to ovulation is not produced.

Women may metabolize fat a little differently than men. Females seem to utilize more fat to produce energy than males, who tend to use the body's stored sugars more readily. In women, this has the effect of slowing down glucose metabolism, meaning that more sugars are available for prolonged exercise. This difference may result in a greater tolerance for endurance events in women.

Media Activity 12.5 Muscle Mass Data

Figure 12.12 Swimmer in streamline position. Fat makes a woman's body smoother and more buoyant.

Figure 12.12 Swimmer in streamline position. Fat makes a woman's body smoother and more buoyant.

The increased body fat that provides increased endurance may also be a physical advantage for women in long-distance swimming events—fat increases buoyancy and enables women to maintain the most energy-conserving streamlined position with less effort (Figure 12.12). In addition, fat provides increased insulation, thus slowing the rate of body-heat loss, and stores energy that can be converted to ATP during endurance events.

Women have improved their performance in endurance events more than men in recent years. For example, in 1972—the first year women were officially allowed to compete in marathons—the first-place woman won the Boston Marathon in a time of 3:10:26. That same year, the first man to cross the finish line did so with a time of 2:15:39. In 2002 the first-place woman finished with a time of 2:20:43, a difference of almost 50 minutes; the first-place man finished with a time of 2:09:02, only a six-and-a-half minute difference. In 30 years, women have made substantial athletic gains, bringing the finishing times of men and women closer together. This could simply be due to training; men have been training longer than women have and they once had access to better coaching and practice facilities. Whether or not this trend continues, ultimately making women faster than men at endurance events, remains to be seen—but men still have the advantage when it comes to events requiring a high level of intensity over a shorter period of time due to sex differences in the cardiovascular system.

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