Another myth is that you have to acclimatize to cold, just as you do to heat. It’s true that peoples’ bodies adapt to hot weather and that adaptation makes people feel better when they exercise in the heat. It also improves performance. With heat adaptation, you sweat more profusely, your sweat is less salty and your blood volume increases.

But exercise physiologists find only modest adaptation to cold. The body’s main responses to cold — constricting blood vessels near the skin, shunting blood to the body’s core and shivering — do not improve if you spend more time in the cold. Nor are the physically fit any better at adaptation than the sedentary.

“Right now, we’re not sure if there is any degree of habituation,” said Robert Kenefick, a research physiologist at the Army Research Institute of Environmental Medicine.