For a species that prides itself on its athletic prowess, human beings are a pretty poky group. Lions can sprint at up to 50 m.p.h. when they're chasing down prey. Cheetahs move even faster, flooring it to a sizzling 70 m.p.h. But most humans—with our willowy spines and awkward, upright gait—would have trouble cracking 25 m.p.h. with a tail wind, a flat track and a good pair of shoes.

Nonetheless, the human race is undeniably becoming a faster race. Since the beginning of the past century, track-and-field records have fallen in everything from sprints to miles to marathons. The performance arc is clearly rising, but no one knows how much higher it could climb. At some point, even the best-trained body simply has to up and quit. The question is, just where is that point, and is it possible for athletes, trainers and scientists to push it higher?

By almost any standard, the best yardstick for measuring how steadily—if slowly—athletic performance has improved is the mile run. In 1900 the record for the mile was a comparatively sleepy 4 min. 12 sec. It wasn't until 1954 that Roger Bannister of Britain cracked the 4-min. mark, coming in six-tenths of a second under the charmed figure. In the half-century since, uncounted thousands of mile heats have been run, yet less than 17 additional seconds have been shaved off Bannister's record—about a third of a second per year.

The credit for the improvement goes mostly to better training and equipment, but shoes and diet can get only so good before they—and the runners—hit a wall. "It's conceivable the record could be 3 min. 30 sec. in 50 years," says American Olympic miler Steve Holman. "But bringing it down much more is a long way off." Scientists agree. In 1987 researchers at Canada's McGill University developed a mathematical model that predicted a world mile record of precisely 3 min. 29.84 sec. in 2040.

All bets are off, however, if genetic engineers find a way to intervene. What slows the human body down is less the architecture of its skeleton than the chemistry of its muscles. The key to speed is making muscles contract faster, and the key to that is gassing them up with as much oxygen as possible. "About 80% of the energy used to run a mile," explains physiologist Peter Weyand of Harvard University, "comes directly from oxygen."

Muscles process oxygen through cellular components known as the mitochondria. Human mitochondria take up only about 3% of the space in a cell. But in animals that run the fastest, mitochondria are far bigger; the mitochondria of an antelope—an animal that easily runs a 2-min. mile and does so in wispy mountain air 7,000 ft. up—are three times larger than ours. "If you could genetically engineer humans to have more mitochondria, bigger hearts and more blood vessels," says Weyand, "we might run about 40 m.p.h."

MORE>>

PAGE 1 | 2