What Exercise Science Doesn’t Know About Women

~Gretchen Reynolds

Several years ago, Dr. David Rowlands, a senior lecturer with the Institute of Food, Nutrition and Human Health at Massey University in New Zealand, set out to study the role of protein in recovery from hard exercise. He asked a group of male cyclists to ride intensely until their legs were aching and virtually all of their stored muscle fuel had been depleted. The cyclists then consumed bars and drinks that contained either mostly carbohydrates or both carbohydrates and protein. Then, over the next few days, they completed two sessions of hard intervals. One took place the following morning; the next, two days later.

Dr. Rowlands found that the cyclists showed little benefit during the first interval session. But during the second, the men who ingested protein had an overall performance gain of more than 4 percent, compared with the men who took only carbohydrates, “which is huge, in competitive terms,” Dr. Rowlands says. Other researchers’ earlier studies produced similar results. Protein seems to aid in the uptake of carbohydrates from the blood; muscles pack in more fuel after exercise if those calories are accompanied by protein. The protein is also thought to aid in the repair of muscle damage after hard exercise. Dr. Rowlands’s work, which was published in 2008, was right in line with conventional wisdom.
Not so his latest follow-up study, which was published online in May in the journal Medicine and Science in Sport and Exercise and should raise eyebrows, especially lightly plucked ones. After his original work was completed, Dr. Rowlands says, “we received inquiries from female cyclists,” asking to be part of any further research. So, almost as an afterthought, Dr. Rowlands and his colleagues repeated the entire experiment with experienced female riders.
This time, though, the results were quite different. The women showed no clear benefit from protein during recovery. They couldn’t ride harder or longer. In fact, the women who received protein said that their legs felt more tired and sore during the intervals than did women who downed only carbohydrates. The results, Dr. Rowlands says, were “something of a surprise.”
Scientists know, of course, that women are not men. But they often rely on male subjects exclusively, particularly in the exercise-science realm, where, numerically, fewer female athletes exist to be studied. But when sports scientists recreate classic men-only experiments with distaff subjects, the women often react quite differently. In a famous series of studies of carbo-loading (the practice of eating a high-carbohydrate diet before a race), researchers found that women did not pack carbohydrates into their muscles as men did. Even when the women upped their total calories as well as the percentage of their diet devoted to carbohydrates, they loaded only about half as much extra fuel into their muscles as the men did.
Why women respond differently seems obvious. Women are, after all, awash in the hormone estrogen, which, some new science suggests, has greater effects on metabolism and muscle health than was once imagined. Some studies have found that postmenopausal women who take estrogen replacement have healthier muscles than postmenopausal women who do not. Even more striking, in several experiments, researchers from McMaster University in Canada gave estrogen to male athletes and then had them complete strenuous bicycling sessions. The men seemed to have developed entirely new metabolisms. They burned more fat and a smaller percentage of protein or carbohydrates to fuel their exertions, just as women do.
What all of this emerging science means for women and the scientists who study (or ignore) them is not yet completely clear. “We need more research” into the differences between male and female athletes, Dr. Rowlands says. In his own study, a particularly intriguing and mysterious finding suggested that the female cyclists somehow sustained less muscle damage during the hard intervals than the men did. Their blood contained lower levels of creatine kinase, a biochemical marker of trauma in muscle tissue. Did estrogen protect the women’s muscles during the riding? And if so, why did the female cyclists who ingested protein complain of sore and tired muscles during the sessions? “Honestly, I don’t know,” Dr. Rowlands says, adding that he does not think that his findings suggest that women should skip protein after exercise. “It’s true that we didn’t see evidence for a benefit,” he says. But his study was one of a kind. The findings need to be replicated.
In the meantime, female athletes should view with skepticism the results from exercise studies that use only male subjects. As Dr. Rowlands says — echoing a chorus of men before him — when it comes to women, there’s a great deal that sports scientists “just don’t understand.”