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According to legend, the only participant in the first marathon (490 BC) was a soldier who ran from the Plains of Marathon to Athens to announce the victory of the Athenians over the Persians in a battle which marked a turning point in the Greco-Persian War. That runner died upon delivering his message ("Niki" = "victory"), and so became an icon of loyalty, endurance and, it would seem, exertional heat injury. (Marathon champion Frank Shorter is reported to have muttered, at the 16-mile mark of one race, "Why couldn't Pheidippides have died here?") Since the revival of the Olympic Games in Athens in 1896, long-distance running as exemplified by the marathon has been the subject of extensive scientific research. Physical fitness is determined by one very simple measure: The ability to take up oxygen. The more fit an athlete is, the greater is his ability to take up oxygen. A metabolically-normal resting adult will take up 3.5cc of oxygen per kilogram of body weight per minute. (3.5 cc/kg/min is also known as one metabolic unit, or MET.) A 154-lb adult at rest would use 225cc of oxygen per minute. With exercise, the athlete's metabolic rate increases, and oxygen consumption must rise. Humans are very inefficient machines, though: 80% of the energy produced is wasted as heat, and only 20% is converted into mechanical energy. Relative degrees of physical fitness vary with age: What is outstanding fitness for an 80 year old is mediocre for a 16 year old. The ability to exercise to an oxygen uptake of 14cc/kg/min is a cutoff point for suitability for heart transplantation. Patients who can reach this level of performance do just as well with medication as they would do with a new heart. In patients with coronary artery disease, the ability to exercise to an oxygen uptake of 35cc/kg/min is associated with a good long-term outcome, regardless of the severity of underlying coronary artery disease. Quantitatively, elite long distance runners are quite different from the rest of humanity. Steve Prefontaine's maximum oxygen uptake of 97cc/kg/min is the best we have encountered, and is nearly 3 times that of a fit adult. By comparison, a men's marathon run in 2:13:00 in ideal conditions requires an oxygen consumption of 76.2cc/kg/min. In other words, a top marathoner can sustain for more than 2 hours twice the maximum oxygen uptake of an ordinary, fit adult. Since 80% of this metabolic energy is being given off as heat, heat dissipation becomes a critical issue for the long-distance runner. Heat balance is determined by 7 factors:
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