This fall, the Stanford football team and the San Francisco 49ers began using Rapid Thermal Exchange (RTX), a new cooling system for athletes invented by two Stanford scientists. Normally, when athletes are overheated, they stand in front of giant misting machines or dump buckets of ice water over their heads. But they shouldn't. These methods are not only an inefficient way for an athlete to cool down, but they can actually be quite dangerous.

Take the case of Korey Stringer. When the Minnesota Vikings offensive tackle died in August 2001, his body temperature was nearly 109 degrees. He had been practicing in sweltering heat and, after vomiting three times, he left the field and sought relief in an air-conditioned trailer. There, he lost consciousness for good, eventually dying of multiple-organ failure brought on by heatstroke.

In the months after Stringer's death, Stanford's Craig Heller and Dennis Grahn conducted a series of experiments on ''exertional hyperthermia'' and the methods for combating it. What they found was surprising. Bringing someone suffering from hyperthermia into a cool environment, it turns out, is precisely the wrong thing to do. When warm skin encounters coldness, the blood vessels near the surface of the skin constrict. Heat becomes trapped inside the body and is redirected to the core, which causes a spike in temperature.

RTX, known informally as the Glove, cools athletes from the inside out, rather than the outside in. It is premised on the little-known fact that our palms, along with the soles of our feet and our cheeks, are ''natural mammalian radiators,'' as Heller puts it. When the body is overheated, it naturally increases blood flow to the palms.

The Glove consists of an airtight, transparent chamber shaped like a giant Dustbuster, inside of which is a metal plate, resting on top of a pool of circulating cool water. A wilting athlete puts his or her hand into the chamber and places it on the plate, which is usually about 70 degrees. A mild vacuum pressure further increases blood flow to the hand. After the blood has been cooled in the athlete's palm, it returns through the veins directly to the heart, and is then circulated to overheated muscles and organs, cooling the body, according to trials, by more than three degrees in 10 minutes.

The system, which is being marketed by AVAcore Technologies, will sell for approximately $3,000 per unit. The biggest obstacle the inventors may have to overcome is the flip side of the paradox that killed Korey Stringer: because RTX cools gently, and from the inside, it doesn't feel immediately refreshing. ''I thought it was hocus-pocus,'' said Kyle Matter, a Stanford quarterback. ''But I tried it when my legs were cramping, and it brought my legs back.''