The Skinny on Humans and the Cold

I've heard that Alaska mountain-climbing legend John Waterman prepared for a solo winter ascent of Denali by lying in a tub filled with ice water. Whether Waterman's chilly soak is fact or embellishment, the ice bath nonetheless inspired me to research the cold tolerance of humans.

Over the years, many people have shed their clothes for the sake of human cold-tolerance research. Many of those people were in the Army or the Air Force. Military leaders were interested in ways to prepare infantryman for cold-weather warfare in the Arctic. Other studies were performed out of pure interest, such as several by the late Laurence Irving, a well-known Alaska scientist.

Irving, a former professor of zoophysiology at the University of Alaska Fairbanks, in 1960 noticed with great curiosity two UAF students who walked around campus barefoot, even in winter. In accordance with their religious beliefs, the students wore only light clothing and wore no shoes or socks. Irving detailed the study in his book, Arctic Life of Birds and Mammals, Including Man.

Irving convinced the students to sit for him in a room cooled to about 32 degrees. The students were allowed to wear light clothing, and Irving measured the temperatures of their fingers, toes and chest as they sat for an hour and studied.

For comparison, Irving recruited a "vigorous young airman" to undergo the same test. After 30 minutes, "the airman's toes became so painful and he began to shiver so violently that I caused him to terminate the test lest he shake himself apart," Irving wrote.

The students who walked barefoot on snow every day didn't begin shivering until after almost 50 minutes in the room. Irving also noticed the cold-adapted students were very conscious of what happened to their bodies, unlike the numb airman. Their fingers and toes experienced cycles of cooling and warming. Every time their fingers and toes dropped to about 50 degrees, the students felt a tingling of warmth, which was followed by a steady rise in the temperatures of their fingers and toes to about 68 degrees.

The study was an illustration of how humans can acclimate their bodies to cold weather and eventually feel little pain while walking barefoot in the snow, Irving wrote.

Human beings can be considered tropical animals, according to Jacques LeBlanc, a Canadian physiologist who wrote "Man in the Cold." Since no studies have been published on what temperatures a human can reach before perishing, LeBlanc wrote that unclothed humans can be compared to rats, who freeze to death when temperatures drop to about 5 degrees Fahrenheit.

Among LeBlanc's studies was the long-debated question of whether fat people stay warmer than skinny people. LeBlanc persuaded six people with varying waistlines to strip naked and endure a temperature of 50 degrees for over an hour. LeBlanc found that a man carrying four inches of subcutaneous (just under the skin) fat didn't start shivering until standing for an hour. A man with less than an inch of body fat started shivering after just 20 minutes. Studies on swimmers of the English Channel also showed that swimmers with more fat had higher body temperatures as they swam than did thinner swimmers. LeBlanc concluded that subcutaneous fat acts as an insulator that retains body heat.

Rather than soaking in a glacial tub, perhaps John Waterman could have gorged himself to achieve the same warming effect. But then he'd have to carry all that insulation up the mountain.