Mindful of the race's start in about 24 hours, Larsen rushed to the athlete's dining hall at the Olympic Village, where he found an American working behind the counter. She surreptitiously stashed the specially designed vests in a walk-in freezer.

The next afternoon, the chilled vests arrived at the start line of the marathon in a cooler. Distance-running star Deena Kastor and her two American teammates strapped them on, then sat alone, shivering, in an air-conditioned locker room as most of their rivals warmed up by jogging in the ferocious, nearly 90-degree heat.