THE BODY MASS INDEX EXPLAINED.
Over time, science and people keep (or should I say kiip) looking for ways to estimate and assess a person's health in non-invasive ways. One of the ways to estimate a person's health through their weight is the body mass index, or BMI for short.
Originally, BMI is calculated by dividing a person's body weight in kilograms (1Kg = 2.2lbs) by their height squared or to the second power, in meters (1 meter = 100cm = 3.28 feet or 39.37 inches). The assumption of BMI as a tool is that mass is symmetrically distributed around the vertical axis of the body. The vertical axis of the body is an imaginary axis (line) that begins at the head, and runs all the way to the ground. For purposes of discussion of symmetry, it is meant to run down the middle of the body.
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Using American units, BMI is calculated by dividing the person's body weight in pounds (lbs) by their height in inches squared or to the second power, then multiplying the outcome by 703. A reminder that one foot is equal to 12 inches. Thus, a person that is 183 cm tall, is 1.83 meters tall, 6 feet tall, or 72 inches tall. 1 inch = 2.54 cm, and 1 foot = 30.48 cm.
The BMI scale spans from zero (in theory only) to infinity (in theory). realistically, a person will have a BMI less than 18.5 Kg/m2 if suspected under-weight (UW); 18.5 - 25 for suspected healthy people; 25.01 - 30 if you are suspected of being over-weight (OW); 30.01 - 35 if you are suspected of being obese stage I; 35.01 - 40 if you are suspected of being obese stage II; A BMI greater than 40 means you are suspected morbidly obese (MO).
Being under-weight or being obese can come with a clinical meaning. A BMI of less than 18.5 can mean that a person is anorexic the lower their BMI is (yet not necessarily so). A BMI greater than 40 (being morbidly obese) increases the risk that the person's body weight becomes a prime reason for death (morbid means deadly or lethal), and serves as one of the criteria for being approved for bariatric surgery.
While you may calculate BMI, I would warn you NEVER to interpret BMI without knowing how the person's looks like currently. Since the calculation for BMI (regardless of which unit of measurement is used) depends on a person's weight, and weight itself is simply the mathematical result of mass times local gravity, then anything of weight will influence the BMI calculation.
Yet, BMI assumes (incorrectly) that if you are over-weight or obese to any extent, that the high value is because of excessive fat mass (more fat than considered healthy). The problem is that people can be of heavy body weight and not be fat (fat in the meaning of high body fat percentage; excess fat tissue to an unhealthy extent).
Since skeletal muscle mass weighs 1.7 times more for the same volume (cubic inch or cubic cm), athletes with excessive skeletal muscle mass weigh more than the average untrained person, and end up having a BMI indicative of being over-weight or perhaps even obese. This, in spite of possibly having normal or perhaps low body fat percentage.
Furthermore, BMI can be problematic due to its dependency on body weight, since a person the is weighed just after eating could "come out" over-weight rather than suspected healthy, just as a person dehydrated or fasting, can come out suspected healthy or under-weight, though it is not true.
Since BMI assumes symmetry around the vertical axis, and since people are not completely symmetrical, BMI has a basic bios to it as a scientific and professional tool. Without explaining it in depth, dividing a person's body weight by their height has an inherent mistake, since a relationship between the two already exists. A person missing a limb does not comply with the assumption of symmetry inherent to BMI.
Furthermore, a prosthetic limb in some cases could weigh more than an original limb, increasing a person's BMI, even if weighed into the calculation, while a prosthetic limb in some cases could weigh less than an original limb, decreasing a person's BMI, even if weighed into the calculation.
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Additional limitations to the use of this specific BMI scale include women that are pregnant, while they are pregnant and some weeks after; Non-biologically matured people, especially children; and not measuring weight under the same exact conditions. While not very realistic, the person's weight should be measured while naked, and the height measured barefoot.
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