Tuesday, September 27, 2005

Ideal Body Weight for Diving, Scuba Calories

In response to a question about diving and obesity - here is an answer giving the ideal body weight for diving:

Edmonds, in the book, Diving and Subaquatic Medicine, states that weight should be less than 20 % above the average ideal weight for age, height and build. Obesity is undesirable because it increases the risk of decompression illness, there being an increase in nitrogen absorption of 4.5 times in fat. Sport diving is more lenient than commercial in this regard in that the bottom times can be reduced according to the percentage that the candidate's weight exceeds that expected for height and build.

Body mass index (BMI) is a method for determining the percentage of fat. It is determined by weight in Kg divided by height in meters squared.

In some areas of the world where medical fitness is more stringently regulated than the US, a high BMI (body mass index) would deter one from diving. Complicating conditions of adiposity include diabetes mellitus, dyslipidemia or hypertension and their associations with coronary artery disease. The BMI is important to divers due to the fact that people with high BMI are more prone to coronary artery disease and an untoward coronary event while diving. A BMI above 30 kg/m2 is thought to be excessively risky for diving. Of course, measured %BF can sometimes show that the diver is quite large and muscular and this needs to be taken into consideration. Figure your BMI by going to this web site:
http://www.nhlbisupport.com/bmi/bmicalc.htm

In one of our newsletters, reference was made to the approximate number of calories burned while scuba diving. The figures quoted (393 kcal for a person weighing 130 pounds, 413 kcal for 155 pounds, 604 kcal for 190 pounds) were all estimates but seemed inordinately high to some people who felt that scuba diving was essentially a sedate activity in a weightless milieu.

In researching a valid answer to this question we came up with some data that hopefully explains the burning of oxygen - and thus calories (kcal). There are quite a few variables in the equation, such as water temperature, level of fitness of the individual, size and body configuration of the diver, current, surge and buoyancy. Swimming energy is also proportional to the square of the velocity and workloads for higher use are tolerated by only the very fit.

Maximum burning of oxygen in the very fit is 40ml/kg/minute (VO2). Resting VO2 is 3.5ml/kg/min. or 1.5-2 kcal (1 MET). All things being equal, the act of scuba diving at a speed of 1 knot burns about 25 ml/kg/min of O2 (about 60% of maximum), the diver moving about 70 feet per minute. (Bove, ’Diving Medicine’, 1997).

A resting value of 3.5ml/kg/minute interpolated to 25 ml/kg/min is 8 kcals/min. A diver swimming for one hour at this rate would burn 480 calories, depending upon any or all of the variables noted above. See also: Nutrition and Diving


Best regards for safe diving!
Ern Campbell, MD
Scubadoc's Diving Medicine
http://www.scuba-doc.com