You can also simply hold on to the Coldfront or Cool Girls packs. The palms—which are hairless and full of blood vessels that lie close to the surface—are an efficient place for the body to shed heat. "They turn into little radiators," says H. Craig Heller, a biology professor at the Stanford University School of Medicine. Heller and his colleagues have shown that cooling hands with a special mitt can boost athletic performance and endurance, and delay the onset of fatigue. Our muscles start to falter when we overheat, but in one of their studies
, those who consistently cooled their hands for three minutes between exercise sets were able to do significantly more push-ups and pull-ups at the end of the three-week trial than when they started.