Women will never run a marathon faster than men, a sports scientist tells Time. Although women have higher body-fat ratios and presumably a larger emergency energy store, females do not have the muscular power that males have, and that may be the "differentiating factor." When matched for weight, men outrun women by average speeds of 10%.
"You have to have testosterone in your body for 20 years to develop the strength that the Kenyan male runners have," the exercise professor says. "I suppose if you could genetically engineer women—if you could put men's muscles into them—they could be as fast."