“It’s interesting—not what you would expect,” murmurs Sue Jesch, Smartwool’s design director. The diagrams scattered across the table before her look like pages from Gray’s Anatomy, with front and side profiles of men and women painted with blotches of color. Some pages map out sweat zones. Others depict variations in temperature. “Women run pretty hot in their top half,” says Jesch. “Maybe that’s a childbearing thing. Nature wants to keep that womb warm.”
In 2011, VF Corporation, the parent company of Smartwool and The North Face, commissioned a 1,200-person study examining how women and men respond to exercise in hot and cold temperatures. Sensors on subjects’ skin recorded surface temperature and perspiration rates, while questionnaires determined where on their bodies subjects thought they ran hot and cold, so researchers could compare perception against reality.
Turns out women run warmer than they perceive. The study found that in winter, women’s coldest zones are the backs of our hands, our glutes, our outer arms, and, oddly enough, our kneecaps. Our upper backs, calves, collarbones, and pelvis actually emit lots of heat during stop-and-go, cold-climate activities like skiing. During hot-weather exercise, women’s legs are markedly cooler than their upper bodies, while men are more evenly balanced. And women’s feet are always colder than men’s, regardless of the outside temperature.