Extra fat weight provides divers benefits such as increased buoyancy, extra padding and insulation. However, some diving authorities have pinpointed the health problems and increased risk of decompression sickness due to body fat. There are several simple and sophisticated methods in measuring body fat.

Some divers worry when they don’t fit into their tightest wetsuit. Others don’t worry until they can’t fit into the dive boat. A quick look around most dive boats reveals that being a little plump seems to be the norm among divers. Is that all bad?

When Does Fat Help In Sports?

Success in different sports depends on characteristic body sizes and compositions. Football linemen almost always have more than an average amount of fat compared to other athletes. Fat weight is an advantage to linemen for the added mass and padding for blocking ability. Increased muscle mass accompanies the extra fat weight to carry the whole package around.

Sumo wrestling is another sport where extra fat weight helps. Linemen and sumos don’t have to run around much. It’s not a big disadvantage to carry extra weight. Other sports where the players have more fat than average athletes are baseball, discus throwing, ice hockey and swimming.

When Does Fat Hinder Sports?

Extra fat weight is a burden to carry across distance or against gravity. The high calorie cost of transporting extra weight makes low body fat advantageous to running, gymnastics and climbing. World class distance runners almost always have extremely low body fat. Runners and gymnasts, along with boxers and wrestlers, often adopt unhealthy dietary restrictions trying to keep their weight low enough to help them in their chosen sport.

What About Diving?

Divers are not known as a skinny minny bunch. That’s not entirely bad. Fat helps selected aspects of diving. Fat keeps you warm in cold water. You don’t have to be obese to reap the thermal benefits. Any amount of fat adds insulation. In those with quite a lot of extra fat, the body puts on more muscle to carry it all around, furthering the thermal advantage in cold water and usually increasing overall strength. Fat increases buoyancy, adding safety and comfort to long swims. Extra padding under heavy equipment cushions the burden. High body weight, whether from fat or lean, provides the loading your bones need to stay dense and strong. Obese people have low rates of osteoporosis.

The same fat that keeps you warm in the cold makes you warm in hot weather, too. One predisposing factor to overheating is being large, round and fat. For divers, overheating is more a problem on the boat or beach than underwater. Extra fat weight is more work to carry around. That, too, is more a problem topside than in the water, where buoyancy rules and you rarely need to go anywhere fast. So what’s the beef, so to speak?

Several past posts described the woes of being overfat  –  the orthopedic problems, the risk of heart attack, stroke and some cancers, the gastrointestinal problems and higher incidence of snoring. Cosmetically, the modern preference for a lean athletic silhouette seems, in many circles, to have replaced the full bodied, corpulent, turn of the century ideal.

If the health and perceived beauty risks don’t faze you, try this on for size: less bottom time. Some diving authorities feel that being fat increases the risk of decompression sickness, although the underlying specifics have not been separated out to satisfaction. They recommend that fat divers reduce their bottom time as a safety margin. The Australian Diving Medical Centre has, for many years, reduced bottom time in proportion to extra weight. A diver overweight by 20 percent loses 20 percent of allowable bottom time. A diver who should weigh 170 for his height and frame, but weighs 204, shortens a 50 minute bottom time to 40 minutes. The same diver, if overweight by one-third, winds up with only 33 minutes’ bottom time. This is in addition to recommendations to reduce bottom time by 10 percent for every 10 years after age 30.

For divers, a balance between not being too fat and not being too skinny is a sport specific goal. How do you know how fat you are?

Are You Fat?

Many divers carry more than the recommended amount of body fat. How do you know if you’re one of them? There are many tests, some you can do yourself at home or in the gym with simple equipment. Others require sophisticated measurement machinery run by skilled operators and interpreters.

APPLES AND PEARS: Where you carry your fat is as important or more so than how much you have. The apple versus pear test requires only a mirror. Carrying fat primarily in the upper body and abdomen gives an apple shape to your figure. Fat distributed on the hips and thighs makes a body more pear shaped. Apple shaped people have a greater risk of obesity related disease like heart disease, colon cancer, diverticulitis, diabetes and high blood pressure than the pear shaped – beer bellies are more a health risk than thunder thighs.

WAIST TO HIP RATIO: The waist to hip ratio test further defines the apple vs. pear test. Take your waist and hip measurements. Divide the waist by the hip measurement. Answers above 0.8 for women and 1.0 for men indicate a tendency toward the more problematic apple shape. For example, waist 37 inches, hip 36 inches (94 cm and 92 cm). The answer is 1.03, not good for anyone.

INSURANCE TABLES: One way to predict health, according to insurance companies, is to check your weight against values in tables telling the ideal weight for your height. According to the height and weight tables of the Metropolitan Life Insurance Company, if you are more than 20 percent above their supposed ideal weight, you are obese. Exercise scientists recommend against relying on insurance tables as there were problems in the procedures for developing them and, like other tests limited to height and weight, they ignore relative fatness.

BODY MASS INDEX: The Body Mass Index (BMI) compares how heavy you are relative to your height. To calculate BMI, divide your weight in kilograms by your height in meters squared. According to this test, if your BMI is more than 25, you are fat. Above 30, you are obese. At 5 foot 10 inches (1.78 meters), a weight above 174 pounds (79 kg) is fat, above 209 pounds (95 kg) tips your BMI past 30. At 5 foot 4 inches (1.63 m) your BMI passes 25 at weights above 146 pounds (66 kg) and 30 at weights above 175 pounds (80 kg). This test does not distinguish very muscular people from those who are overfat, and misses light, yet high fat people.

SOMATOTYPING: Height and weight tests do not account for musculature and body dimensions. Somatotyping is a method of classifying your body according to three characteristics – thinness, fatness and muscularity. Thinness is called ectomorphy. Fatness is called endomorphy. Muscularity is called mesomorphy. Each type has specific characteristics of limb and body dimensions, with varying proportions of fat, bone and muscle.

Everyone is a mixture of the three types in differing amounts. Some people predominate in one type, giving them the long, linear and delicate appearance of the ectomorph; the round, soft and short necked look of the endomorph; or the hard, square and rugged muscled body of the mesomorph. In football many players score high in both mesomorphy and endomorphy. Swimmers are usually endo-mesomorphs. Gymnasts are usually ecto-mesomorphs. Sprint runners score higher in mesomorphy than distance runners.

Casual somatotyping is done by the eyeball technique. Complete somatotyping requires trained analysis, photographs or close inspection of naked subjects in three planes, caliper skinfold measurements, reference tables and equations. Coaches use somatotyping to identify those who would excel in different sports. Somatotyping helps physicians identify those body types with specific disease tendencies. Male mesomorphs and endo-mesomorphs have higher predisposition to coronary artery disease than male ectomorphs.

ANTHROPOMETRICS: As part of somatotyping, or as a separate assessment, the size of the body’s frame is determined with calculations using measurements of bone lengths and widths. Knowing frame size helps determine optimum weight. One test, the Health-Carter, measures elbow and knee widths and biceps and calf circumferences. Another, the Skeletal Frame Technique, measures widths of the shoulders and hips. The Tipton technique computes the minimum healthy weight for a given frame based on width and depth of the chest and width of the ankle, wrist and hip at two sites.

INDEX TESTS: The Ponderal Index is your height divided by the cube root of your weight. Ponderal Index is used to determine degree of endomorphy. The Quetelet Index is another simple index of general body proportion. The Circumference Test is nothing more than the familiar tape measure around the waist, hips, chest, leg, arm or whatever.

THE JIGGLE TEST: Jump in the air. When you land, see how long it takes for all your parts to stop jiggling. Higher times indicate higher fat amounts.

Why Measure Percent Body Fat?

A slender looking person of normal weight can have a high amount of body fat. A person weighing above average for their height may have heavy musculature and little body fat. The second person is above average weight, yet low body fat. The first is normal weight and overfat, even though not seeming to be. The distinction lies in their amount of body fat relative to their total weight.

Percent body fat loosely relates to overall physical health. How it relates to diving health is not as well defined. Moreover, two divers may be the same height and percent body fat yet have different total amounts of fat. Take two divers, each 5 foot 10 inches tall, both with 20 percent body fat. One is 150 pounds and has 30 pounds of fat. The other is 250 pounds with 50 pounds of fat. The larger diver has more total pounds of fat.

The distinction between percent fat and total pounds of fat may have some bearing on the popular yet unsubstantiated assumption that women’s risk of decompression sickness may differ from men’s owing to higher characteristic percent body fat. A larger man may have more total pounds of fat. A 120 pound woman with 20 percent fat carries 24 pounds of fat. A 180 pound man with only 15 percent fat tops that with 27 pounds of fat. The three pound margin is 12.5 percent more fat weight for the man. A 200 pound man with only 15 percent fat lugs around 30 pounds of it and rare is the 200 pound male diver with only 15 percent fat. It is not known if percent fat or total fat weight matters more in decompression sickness or even if either contribute directly.

Measuring Percent Body Fat

Several tests determine how fat you are. These are called body composition analysis. Accuracy of some tests is poor, others moderate to excellent. Although the average body fat percent usually quoted is 15 percent for men and 25 percent for women, recent studies reveal the average American, male or female, is closer to 22 percent fat.

CALIPERS: Calipers are a small, simple and inexpensive instrument. Calipers measure the thickness of your folds of fat at up to ten sites on your body. Simple equations translate the sums of different sites into percent fat. Caliper measurement is painless unless the tester enthusiastically grabs and squeezes. The error of measurement is large, usually about 7 percent, varying greatly with the experience of the tester, making it not a true measure but a gross estimation. Caliper testing is often misused, particularly in health clubs. If a first reading shows 25 percent fat and, weeks later after an exercise program the second reading is 22 percent, it does not necessarily mean the person lost 3 percent fat. The large error of measurement makes it impossible to tell.

CADAVER ANALYSIS: Cadaver analysis is a technique of cutting the body open to directly measure fat stores. Cadaver analysis is not recommended for divers.

HYDROSTATIC WEIGHING: Hydrostatic weighing, also called underwater weighing, is the gold standard of body composition analysis techniques. It has the lowest percent error of all currently used tests. In underwater weighing, you sit on a scale underwater. Your body density is determined from equations after the buoyancy from the air in your lungs (left after you exhale as fully as you can) is subtracted. The final reading is suspect if the person tested is unwilling to exhale completely U/W and hold the exhale for as long as it takes for the tester to get a good measurement.

TECHNO-MARVELS: Sophisticated body composition analysis includes bioelectric impedance, potassium ion determination, ultrasound, near-infrared interactance, CAT scans, creatine absorption, proton absorptionmetry and nuclear magnetic resonance imagery. These tests need further validation and require expensive equipment.


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