# I am looking for any information you might have for hydrostatic weighing.

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I am a Physical Education major. I am looking for any information you might be able to email to me dealing with hydrostatic weighing. I am working on a major laboratory project and could use some assistance. The lab deals with percent body fat, so any additional info on that would help also. I don’t know whether you are willing to do this kind of stuff or not. If so great if not that’s understandable too. Thanks for your time.

It all started with a Greek mathematician named Archimedes who while taking a bath figured out that his body mass determined how much water overflowed his tub. I would suggest you pick up an exercise physiology book by William Katch & Frank Katch or contact an exercise physiologist at your university as this is a learn by demonstration technique.

Hydrostatic weighing is considered by many to be the most accurate means for assessing body fat (fat floats) and muscle mass (muscle sinks) over skinfold caliper or electrical impedance. However bone density also will affect the results as African Americans have the densest bones, Northern Europeans (whites) average and Asian people have the least dense bones.

The water temperature (4 degrees Centigrade or 95 degrees Fahrenheit) affects water density, swimsuit (nylon), hydration and fed status of the participant are critical. In addition, the participant must practice exhaling all the air from their lungs prior to being submerged under water for 5 seconds. (Can you imagine someone telling you to force all the air out of your lungs and then dunk you under water?) This procedure may be repeated 8 to 12 times depending on the participant’s ability to expel air each time. The difference between an obese and lean individual’s results from hydrostatic weighing are small (0.93 and 1.10 grams/milliliter) so the procedure must be done accurately and repeated.

The participant’s weight out of the water is determined and then their weight in the water. Air weight is divided by water weight to determine the person’s specific gravity (density). The above numbers are close to butter and round steak respectively.

Joanne Larsen is a licensed, registered dietitian with extensive clinical experience in nutrition therapy in hospitals, clinics, mental health and long term care. She has a bachelor's degree in dietetics with a minor in chemistry and a master's degree in nutrition with a minor in counseling. She is a member of the Academy of Nutrition and Dietetics (formerly American Dietetic Association).