SO MANY POSSIBILITIES!
Body composition is regarded as one of the fitness components, related to the make-up of the body as it pertains to the tissue types and content of a person's body. We can address the content of a person's body in absolute units of weight (kilograms and pounds), or in relative units, mainly percentage of the whole. It is more common to use the relative unit of percentage. For example. the extent of fat tissue (a.k.a. adipose tissue) is often presented as body fat percent rather than fat mass/weight in pound or kilograms.
Often in science we prefer relative units, ant thus percentages, since they allow more easily to compare between people, sexes, and more. Furthermore, research shows that in many cases related to phenomena of health and fitness, their occurrences correlate to relative measure, rather than absolute measures. For example, it is a person's body fat percentage that correlates to health problems, not their absolute fat mass/weight.
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The basis for all and any body composition analysis methods, is the idea that increased muscle mass and decrease fat mass due to long term adaptations to long term (chronic) healthy exercising and diet, bear with then multiple diverse health benefits. The true and horrible way to know exactly how much fat and muscle mass a person has, would be to take them all out. This requires the person to be dead (we prefer people to be alive), and the conclusions would bear little meaning if at all to a dead person.
Thus, in order to assess a person's health based on their body composition, and to be able to draw as accurate conclusions as possible in order to influence their lifestyle, dietary intake, and exercise prescription plan, we estimate their body fat percentage as externally and invasively as possible. Over the years, several method related to body composition have evolved, each with advantages, disadvantages, and a different ability to accurately estimate body fat percentage, muscle mass, active muscle mass, overall body volume, and more.
The main methods that we as humanity have come up with include 1) Skinfolds measures; 2) Circumference measures; 3) Water displacement (underwater weighing); 4) Air displacement (mainly using the bod-pod); 5) DEXA (dual energy x-ray absorptiometry; a.k.a. bone densitometry); and 6) BIA - Bioelectrical impedance analysis.
Over the next several posts in this mini-series of posts, I will survey each method, how it is used, advantages and disadvantages, the assumptions at the basis of the method, and more. For now, let's briefly explain each method as an introduction and basis for later posts about body composition. Skinfolds measurements are based on an assumed statistical correlation between sub-skin (subcutaneous) fat mass and total body fat mass. Thus, measuring skin folds in anatomical locations where subcutaneous fat mass is the greatest, should best represent the body's total fat mass.
Circumference measurements is somewhat similar to skinfolds in the sense that certain areas of the body will display as greater fat mass, which in turn will increase the circumference of the body part measured accordingly. The assumption is that increased circumference results from increased fat mass, correlating to increase total body fat mass.
Water displacement is a pretty accurate method to assess body composition, based on Archimedes' principle that states that a body immersed in a fluid experiences an upthrust equal to the weight of the fluid displaced. Accordingly, as we get into a tub full of water, the water level rises in a linear correlation to the volume of our body since it is pushed aside (i.e. displaced). Very similar to water displacement is the idea of air displacement. If we enter an area with a known volume of air, air will move to the extent of the volume of the body now entering the same area, and displacing it.
The DEXA sends two low-dose X-rays through the body and its diverse tissue types. Each tissue will absorb the rays differently, and thus can be represented differently visually and digitally by the DEXA machine.It allows to accurately differentiate between bone mass, lean mass, and fat mass. Bioelectrical impedance analysis assumes that electrical currents travel differently through different types of tissue. For example, fat tissue slows down the speed in which an electrical current travels through it, while muscle allow it to move faster. By measuring the time and overall distance that the electrical current traveled, it assumes what it traveled through. To be continued in the next posts of this mini-series; Stay tuned!
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