January 2003

By Selene Yeager

|Related Product| |---| | Buy "Scuba Diving Explained: Questions and Answers on Physiology and Medical Aspects of Scuba Diving" now| Many of us have seen divers so large they can barely pull themselves from the water. Divemasters tell of large scuba lovers linking weight belts together because they can't circle their ample waists with just one. And Dr. Lawrence Martin, M.D., author of Scuba Diving Explained, figures most dive boats sit a little lower in the water these days, because, as he says of his latest excursions, "everyone's overweight."

Well, "everyone" may be a slight exaggeration--but only slight. According to the latest data from the Centers for Disease Control and Prevention, almost one-third of Americans are now obese, and more than two-thirds are overweight. We know extra poundage hurts your health on dry land. But at what point should weight keep you docked from diving?

"Being overweight or even obese in and of itself doesn't mean you can't dive," says Dr. Martin. "But there are risks to consider and special precautions to take. Plus, there's certainly a minimum level of fitness that divers should maintain to keep the sport safe."

The Heart of the Matter

Hands down, the biggest risk overweight divers face is heart attack--one of the most common causes of sudden death under water in all divers, regardless of their wetsuit size. It's general knowledge that when you exert yourself, whether it's by freestyle swimming or bailing a boat, your heart must pump harder to deliver oxygen-rich blood to your working muscles. But what most divers don't consider is that the mere act of dunking your body in water puts your pump under increased pressure, as the amount of blood flowing into your heart's chambers increases. Add to that the pressure from sucking high-density gas through a regulator, and your heart is churning on all cylinders before you even start your descent.

"Diving isn't like running a marathon, but it has all kinds of exertion people don't consider," says dive doc Ernest Campbell. "Carrying heavy gear, climbing ladders and swimming can force your heart to beat pretty hard."

If you reach a point where the heart itself can't get enough blood, which is a particular risk for overweight people, who often have high blood pressure or other cardiovascular risks, the heart can't function and cells in the heart muscle can start to die--and that, fellow divers, is the "big one," a heart attack. "Divers with a BMI of more than 30--the marker of obesity--are at excessive risk, because they are already prone to coronary artery disease," says Dr. Campbell.

Like a Nitrogen Sponge

Aside from putting undue pressure on your pump, diving with extra pounds also elevates your risk for DCS. If you were to set a pound of muscle and a pound of fat side by side, the muscle would resemble tuna steak--dense, fibrous tissue that's not easily permeated. The fat would look more like a washed up jellyfish, soft and squishy. There's a disadvantage to having too much of the latter, more supple tissue--it sucks up nitrogen. In fact, nitrogen is five times more soluble in fat than it is in lean muscle, so a person who is 30 or even 40 percent body fat absorbs a great deal more of the gas most responsible for DCS than someone whose body fat is in a more healthy 15 to 25 percent range.

"The danger here is that nitrogen loads can become high in adipose [fat] tissue, and bubble formation can be extensive," says Dr. Campbell. "But you wouldn't develop pain from this. Instead, these gas bubbles would be dumped into the blood where they are carried to the heart and lungs. If the gas bubble loads are high enough, you can end up with a serious condition, like a brain embolism."

Excess weight can cause any number of heart and lung problems, says Dr. Campbell. "I've dived with a 375-pound diver who had acute pulmonary edema on one dive and a subsequent coronary event on another."

Fit To Dive

All that said, we've all been aboard with divers (maybe including ourselves) who have the classic aquatic-mammal build, yet seem to dive and survive as happily as their trimmer counterparts. Though excess weight, and certainly obesity, make taking the plunge a riskier proposition, with the right steps you can reduce your risk on every dive, increasing your chances for a longer, healthier dive career. Here's what the experts recommend.

Take some giant strides. The more physically fit you are, the less oxygen you use when you exercise, no matter what you weigh. "Obviously, you have to demonstrate some physical fitness even to get dive certified," says Dr. Martin.

But being able to pass the swim test is a minimum. You should be fit enough to handle unexpected challenges, like swimming against strong currents or having to assist a dive buddy back to the boat. The best way to do that: Commit to a regular aerobic exercise routine, where you're working hard enough to break a sweat for 45 minutes four to five days a week. Even more moderate levels of aerobic activity can boost your overall fitness. "When you can swim several laps in the pool without difficulty, ride a bicycle for a half an hour or jog a half mile without collapsing, you're probably fit for diving," says Dr. Martin. As a bonus, being physically fit also reduces your risk of hyperventilation and panic stress reactions.

Go gear hunting. A wetsuit should be snug. It should not cinch your torso like a neoprene corset. Far too often, large divers squeeze themselves in too-tight wetsuits that constrict their chests and squish their lungs like Slim Jims. This isn't just uncomfortable; it's dangerous, as it makes proper breathing difficult, if not impossible, which not only burdens your heart, but also can lead to carbon dioxide buildup. Many suits come in size 3XL; you can even find 4XL. Invest the time and money into getting a suit that fits you properly.

Ditto for your weight belt and BC. Body fat helps you float, so the more you have, the more weight you'll need to carry to descend. And your BC shouldn't be so tight-fitting that it is difficult to inflate properly.

Err on the conservative side. Remember dive tables were originally modeled after fit, young, buff Navy divers--not sedentary desk jockeys. Overweight divers not only absorb more nitrogen, but they also tend to consume more air than leaner divers because it takes more work just to move through the water. Take this into consideration and dive conservatively. Don't push your depths or bottom time, and make generous safety stops to minimize your risk of getting bent.

What's Your BMI?

The more body fat you have, the higher your risk for heart troubles and DCS. Below is a guide to calculating your body mass index (BMI) a widely used indicator for body fat. Whether you're a new, plus-sized diver gunning for your C-card, or you're a veteran diver carrying a little more to love since your certification, if your BMI is high, pay attention to the tips in this article to keep yourself--and your dive buddies--safe.

Plug your height and weight into the following formula to calculate your BMI:

(Weight in pounds ÷ Height in inches ÷ Height in inches) x 703

So if you're a six-foot-tall, 170-pound diver, your BMI would be 23:
(170 ÷ 72 ÷ 72) x 703

The guidelines for both men and women*:
Underweight: BMI less than 18.5
Healthy weight: BMI of 18.6 to 24.9
Overweight: BMI of 25 to 29.9
Obese: BMI of 30 or more

* If you are very muscular for your height (like a football player), your BMI will register high, though you are certainly fit for diving. This index is based on the average population.