16 Exercise Physiology Exam 41. Know and understand the principle of Archimedes and how it applies to the procedure of human body volume measurements.- This is the trick that Archimedes found out when he had to figure out if a crown was made of solid gold. When an object is submerged in water, it will displace its volume in water. This means that to find the volume of an object, it is placed in water and by seeing how much water it displaces, that is the object’s volume. So we have volume, but how is this related to body comp?! Remember, that mass/volume will give you density, and there is a formula to have the percent of fat using the density. So simply take their mass (weight in Kg) divided by the volume and you will get density. This is the GOLDEN STANDARD!! So when a person is placed in water, the volume of the person is equal to the volume of the water that they displace. This is useful because there is a formula to find percent fat mass from the density of an object. Density is equal to mass/volume. Finding the mass of a person is easy (just weigh them), but this is the easiest way to find the volume of a person. The density is also called the specific gravity. 2. Understand the differences and usefulness of different body composition and anthropometric assessment procedures discussed in the text and class. What are the general assumptions used by indirect measures. - Different procedures exist to measure body composition. Among these are the skin fold, the bioelectrical impedance (BIA), underwater weighing (explained in question 1), x-ray, and Tony Berardi16calculating BMI. Direct means that they are taking it at an autopsy. Clearly, this is not too practical, as your body composition isn’t too useful if someone is doing your autopsy….. (because you are dead!) Everything gone over here are all indirect, and they assume that all mass in the body is either muscle or fat; they don’t take into account water mass, bone weight, or air volume. Skin folds are the most common, and this is based on the fact that most of our fat is subcutaneous meaning that a majority is found at the surface of the body. Using this knowledge,seven skin fold sites are pinched with a caliper, and these numbers are plugged into a formula toget percent of body fat. All the pinches should be made on the RIGHT side of the body. This method is not that accurate (depending on if the tester has no idea what they are doing and how to assess the sites correctly), and can be affected by many things, like exercise (this will increase the thickness of your skin), if you are dehydrated (lack of water will decrease the thickness of the skin) and age. As you age, fat moves to being more visceral, so an old person would be calculated as having less fat. Then we have the underwater weighing. This is the gold standard and yields the best result, but it isn’t that practical (who has a tank of water and a human sized scale sitting around?), like the skin fold is. Fat is less dense than water, so the more fat that someone has, the less they will sink. The BIA is pretty stupid. This is a hand held device that sends a current from one hand to the other. Fat does not contain electrolytes, so it doesn’t conduct current as well as lean mass, which has electrolytes. So the slower the current is at reaching back to the machine, the more fat a person supposedly has, since the lack of electrolytes impedes its travel. As you can probably see, a lot of things can affect this. If you are dehydrated, then you will have more electrolytes in your blood (because of less water) and will conduct the current faster and your body fat will be underestimated. If you are hydrated, the opposite will happen and the fat Tony Berardi16amount will be overestimated. If your skin is warm, then the current will travel much faster and underestimate it, then if your skin is cold, the current will travel very slow. This had me at 2% one time. Clearly not right. And the funny thing is, gyms and health screens use BIA exclusively, and you can see how unreliable this test is…so if you go to Gold’s Gym and they have you do a stupid BIA, and it reads you at 30% body fat, don’t be alarmed! Unless you’re significantly overweight, you are NOT 30% body fat. X-ray will reveal bone mass, and you can calculate fat mass from this. BMI is an anthropometric measurement taken from one’s weight in kg and height in m^2. It is in the units of kg/m^2. This will put someone in ranges of underweight, normal, overweight, and obese. <18.5 is underweight, 18.5-24.9 is normal, 25-29.9 is overweight, and above 30 is obese. But this is not the best measurement for fit people, as it doesn’t take into account muscle, which weighs more than fat. Another anthropometric is waist circumference (girth). This is a really good measurement for the amount of fat that is in the abdominal region. Fat in this region is the best measurement of your risk for heart problems. More fat in the abdominal region leads to insulin resistence, which leads to diabetes, which leads to unnecessary stress on the heart. If you have excess fat, lose it with the goal to be healthy, not just to “look good”. The two common classes are android and gynoid shape Then you can get fancy with the bodpod, a $10,000 machine. The machines measures the volume of the machine and then measures the volume with you in it and finds the difference. This is fairly accurate, yet expensive. I have done a few, and it is pretty freaky sitting in it. It is COMPLETELY silent in there; if you thought you have heard silence before, try to get into this test.Tony Berardi16o So the best one is underwater weighing and waist circumference (for anthropometric). But underwater weighing is the gold standard for measuring % body fat. o The norms are around 15% for men and 26% for women. 3. What are the body composition differences between males and females?- Males have less body fat, because only 3% is essential, whereas 12% is essential in females. This is due to the fact that females need fat for their menstrual cycle and all that good stuff. Women have a more important role then men do: to bring new life into the world and this requires some extra fat!4. Understand the difference between essential and storage fat, and the difference between FFM and LBM.- Essential fat is what the organs need to function properly. This is needed for the bone
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