The Scuba Diver’s Ideal Body

I think we should look towards the anatomy and physiology of marine mammals to answer this question.

Dr. Klaus M. Stiefel

As a scientist, my arguments are meant to be objective and devoid of personal bias. The pursuit of the unprejudiced truth, untainted by my own opinions, is ordinarily my goal.Not this time. I’m sure you can all appreciate the tongue-in-cheek attitude, but despite the jokes, I’m also making some truly valid points here.

What is the scuba diver’s ideal body? I think we should look towards the anatomy and physiology of marine mammals to answer this question.

The Scuba Diver’s Ideal Body

First is the issue of insulation. Mammals generate their own body heat, and wherever they are, in the tropics or in Antarctic waters, their core body temperature remains nearly constant. It is critical for African gazelles to get rid of heat; whales, dolphins and seals in cold, ocean water must preserve it.

One strategy is to grow in size. The surface area of an animal roughly grows with the square of its diameter; volume grows with the cube of the diameter. As a consequence, a larger animal has more volume per surface area, and will lose proportionally less heat via this relatively smaller body surface. This is why whales are gigantic, and even the smallest dolphins and seals are relatively large mammals. Hence, a larger diver is a warmer diver.

Another heat conservation strategy is to use what I call “bioprene,” or body fat. It’s a great insulator, and a decent layer of it will keep you comfortable during extended dives. Whales have massive amounts of blubber, keeping them warm even in the icy waters of the polar oceans. And we humans can take advantage of that strategy as well.

Interestingly, women who, on average, have a higher body-fat percentage than men are better adapted for enduring cold water. Sponge and pearl divers in places with relatively cold water, such as Korea, are traditionally women. A few scientific studies have investigated the physiology of these Korean female divers, and they found that these women have a basic metabolic rate significantly higher than non-diving Korean women of the same age groups: their bodies have learned to burn more calories to keep them warm. Like so many other aspects of the human body, heat generation can be trained. This is why extra millimeters in your wetsuit can be addictive: Once you add more and more neoprene, your body forgets how to burn more calories to maintain a normal body temperature in cold water, and you will have to keep wearing as much neoprene, or add more. I know divers who moved to Hawaii a few years ago, initially diving in a 3 mm shorty, and after giving in to neoprenic temptation, are now swimming above the corals in 7 mm of neoprene with a hood.

While fat is a good insulator, there are disadvantages for a diver. Fewer blood vessels run through body-fat deposits than through other bodily tissues, and hence the gas exchange in blubber is slower. This has implications for decompression — adipose tissue is a “slow tissue,” and the nitrogen you breathe in at depth will stay in your body longer if you have lots of this slow tissue, which is thought to increase the risk of decompression accidents. What do I make of this trade-off between the benefits and downsides of body fat? I think a moderate amount of fat is reasonable for a diver; don’t strive for the rail-thin fashion-model or bodybuilder look if you intend to keep warm. So have another beer and say yes to another scoop of ice cream to build valuable biological-insulation material. Go ahead, a scientist told you to.

Whales have more special adaptations for diving, including a special capillary net in their circulatory system to remove excess bubbles before they can do any damage to vital organs. Until genetic engineering can provide me with one of these, I will have to stick to the non-deco times and decompression schedules computed on my wrist.

There is something else we can learn from marine mammals: they are excellent swimmers. When would-be divers ask me if they must be good swimmers to be divers, the answer is no: being able to swim reasonably well is sufficient. But, as scuba divers, we should nevertheless aim to be as strong as possible in the water. I swim in the ocean — more challenging than a pool — for all of my cardio. No, I can’t swim nearly as well as even the frailest dolphin, nor am I a competitive contender, but I am moving about much better than many other divers. I can confidently kick my way through currents, eddies or breaking waves, and a lengthy surface swim does not tire me out.

Many marine mammals are powerful animals. Have you ever seen two male elephant seals slug it out? A humpback whale breaching? These are great displays of strength, and strength training too is useful for divers. It increases body mass, which keeps you warm (see above), and it surely helps in hoisting tanks around, handing cameras back onto boats and in walking up steps on shore dives with all your gear on. Even if you can do most dives without being particularly strong, being fit can only help if something goes wrong.

So, I argue that the ideal scuba diver is strong and stocky, in shape, but with some subcutaneous body fat, and trained to cope with cold water. Kind of like the guy I see in the mirror every morning.

Have any tips of your own for staying in tip-top shape? We’d love to hear them!