Unconventional exercise

Sometimes called "sprinter's lung" and caused by the sudden and deep intake of bitterly cold air into one's lungs.

I thought it was this...

The reason, of course, is that the human body is adapted, after surviving five major ice ages, to heat air quickly as it passes through the nose and mouth. In fact, the one legitimate lung condition that troubles runners in cold air doesn't come from the cold. In his 10 years of working with Nordic skiers at the U.S. Olympic Committee training facility in Lake Placid, New York, exercise physiologist Ken Rundell, Ph.D., found that as many as 50 percent would develop "skier's hack"--a transient cough--during or after training.
In subsequent research at Marywood University in Scranton, Pennsylvania, Rundell proved that the dryness of cold air causes the "airway narrowing," a term he prefers to the more common "exercise-induced asthma." To diminish this problem, Rundell suggests using a scarf that will trap your natural water vapor when you exhale, and then allow you to "recycle" it when you inhale
A buff helps, but makes your mouth + jaw damp. Which then gets cold.