The Marathon and the Limits of Endurance

The marathon is measured today at exactly 42.195 kilometres, an oddly precise figure with a curious history. Its name comes from an ancient Greek legend. After the Athenians defeated an invading army of Persians on the plain of Marathon in 490 BC, a messenger, traditionally named Pheidippides, is said to have run all the way to Athens to gasp out news of the victory before collapsing and dying on the spot. Whether or not the tale is true, it gave the modern race both its name and its aura of heroic exhaustion. The story may owe more to legend than to history, for the ancient sources disagree and some place a far longer run at the heart of the tale, but its grip on the imagination has never loosened, and the picture of a lone runner spending his last breath on a message has become inseparable from the race.

When the modern Olympic Games were founded, the organisers revived the story as a sporting event, and the first marathon was run at the 1896 Games in Athens over a rough version of the legendary route. The distance was not yet fixed, however, and early marathons varied in length from one occasion to the next. The now-standard 42.195 kilometres was settled only at the 1908 Olympics in London, where, according to the usual account, the course was lengthened so that it could start beneath the walls of Windsor Castle and finish directly in front of the royal box inside the stadium. That extra distance, added almost as an afterthought for the comfort of royal spectators, was later fixed as the official length for all marathons, so that runners ever since have chased a finish line whose exact position was decided by the width of a palace lawn.

Behind the sporting drama lies a deeper biological story, for humans are, by the standards of the animal kingdom, extraordinary long-distance runners. According to what is known as the endurance running hypothesis, our ancestors evolved bodies suited to covering great distances on foot, quite possibly in order to hunt. Rather than trying to out-sprint their prey, early humans may have chased animals at a steady jog until the animals overheated and gave up. A surprising number of features of the human body seem built for precisely this kind of effort. The idea is still debated, but it draws support from the fact that humans, though hopelessly slow over short distances compared with a deer or a dog, can keep going at a steady pace for hour after hour in a way that very few other animals can match.

The most important is the way we keep cool. Most mammals shed heat by panting, which cannot be sustained at full speed for long, whereas humans sweat over a nearly hairless skin, allowing the body to lose heat continuously even while running hard. Springy tendons, above all the Achilles tendon at the heel, store energy at each footfall and return it like a catapult, and the large gluteus muscle of the buttock, unusually big in humans, braces the trunk with every stride. Taken together, these traits make sustained running remarkably efficient. On its own, none of them would be decisive, but combined they add up to a body unusually well tuned for covering ground, a legacy that every marathon runner unknowingly puts to the test.

None of this makes the marathon easy. Somewhere after about thirty kilometres many runners meet what they call the wall, a sudden and crushing fatigue that strikes when the body's store of glycogen, its most readily available fuel, begins to run out. To hold it off, runners train their bodies to burn fuel efficiently and take in carbohydrates, in the form of drinks or gels, throughout the race. Even elite athletes must ration their effort with great care, and the very fastest have pushed the limits astonishingly far: in a specially arranged event in 2019, the Kenyan runner Eliud Kipchoge covered the marathon distance in under two hours, a time so remarkable that it was not accepted as an official record but which showed just how far human endurance can be stretched. Reaching such times demands not only rare natural gifts but years of punishing training, a carefully managed diet and a shrewd sense of pace, and even then the body's limits are never far away, waiting in the closing kilometres for anyone who has misjudged the effort.