The Fitness Fixer
The Fitness Fixer

Three Common Swimming and SCUBA Myths in the News Again

On Monday July 7, a news show Troubled Waters featured a story of two scuba divers who floated 19 hours overnight after they and their dive boat did not connect after a dive on the Great Barrier Reef in Australia.

In their television interview, the two divers told various points of the situation. Three of the concerns were common myths often repeated in scuba training.

1. They mentioned they experienced signs of hypothermia. Technically, not any chilling is hypothermia. Being uncomfortably cold does not mean you have hypothermia. Shivering and teeth chattering does not mean you have hypothermia. You can even become incapacitated by cold before becoming hypothermic. In informal conversation, the two terms of hypothermia and chilling are often used interchangeably.

2. The woman of the pair stated she had read in a book, which had a section about progression of hypothermia, that exercise is not good and can be counterproductive. They were worried that body movement would, "send blood to the muscles away from your core, and your organs" and for that reason, make them colder.

I have read the book they mention. It is a book of wonderful stories and great writing, interesting medicine, but the physiology is frequently off. As a physiologist, I notice these things. When I teach medical students in their classes, I often see that they do not want to learn physiology, they only want to learn what medicine to give and where to cut. I tell them that without understanding the reasons for how the body resulted in the situation in the first place, they will only repeat the mistakes of their teachers by giving medicines and cutting.

Back to the shivering divers floating all night, waiting for rescue. It is not always the case that exercise in the cold must only make you colder. Exercise in cold water can generate enough heat to match or surpass the large thermal drain, depending on water temperature, work load, duration of exposure, your body composition, what you are wearing, and other factors. It is true that exercise in cold water increases heat loss, but it is an important point that it does not mean that you will always cool. Whether you stay comfortable or get cold depends how much heat you keep and how much you lose. If you generate more heat than you lose, you will be warmer than when you started. When I worked on cold water immersion for the Navy, we studied body cooling in pilots downed in cold water, and how long they could survive (all volunteers, really they loved my studies). We also studied divers. Some divers sent for underwater missions during the Gulf War were overheating underwater and had to wear ice vests with their scuba gear.

3. The last myth is a popular one. I am a scuba instructor and have heard this one repeated often. The two divers mentioned that the woman of the pair was menstruating and that there were sharks in the water. The woman said, "I'm shark bait is what I'm thinking." Diver researcher Dr. Carl Edmonds found that Australia's shark attack tracking system reported nine times more shark attacks on men, even though there was an even number of male and female swimmers.

Menstrual blood does not attract sharks. Neither does menstrual blood attract grizzly bears during camping trips, cause wine to sour as stated in ancient religious writings, or cause wings to snap off airplanes, as pilots insisted in the 1920's. The term man-eating shark, for now, remains.

I explain these myths and more about swimming and diving physiology, underwater and in heat and cold, in the book Diving Physiology in Plain English.

Related Fitness Fixer:

Photo 1 divers in cold water from my friends at Naval Medical Research Institute MNRI
Photo 2 of Dr. Jolie Bookspan diving with silly friend
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About the Author


Dr. Bookspan is an award-winning scientist whose goal is to make exercise easier and healthier.