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THERE is one secret to running a marathon: oxygen. And whoever takes the
men’s and women’s gold medals in late September will need a body like a
sponge—one that sucks up oxygen as fast as possible.

Since they’re in the race for the long haul, marathon runners can’t blast
through their reserves the way their speed freak colleagues do. They need oxygen
so that muscles can burn their fuel without tiring. “The muscles of elite
marathoners can take all the oxygen their bodies can throw at them and more,”
says Will Hopkins, a sports scientist at the University of Otago in New
Zealand.

The rate a top marathon runner can take up oxygen is enormous—50 per
cent higher than an average person. The perfect marathoners come endowed with
large lungs and airways that can suck up as much air as possible. Training
increases the size of their heart, allowing it to pump more blood with each
beat, and also increases the number of blood vessels that feed oxygen to the
muscles.

The streamlining of the oxygen assembly line continues all the way into the
invisible world of the muscle cell. A top marathoner’s muscles should have
double the normal number of mitochondria, the cell’s engines, which use oxygen
to burn sugars for energy. “You can think of their bodies as assembly lines
delivering oxygen from the atmosphere to their muscles,” says Susan Ward,
director of the Centre for Exercise Science and Medicine at the University of
Glasgow.

This oxygen superhighway needs the right sort of muscles, however. Fast
twitch muscle fibres are a disadvantage. Instead, slow twitch fibres tend to
make up at least 75 per cent of marathoners’ leg muscles. Slow twitch muscle
fibres use oxygen efficiently and can sustain a lower speed of contraction for a
very long time.