How do you calculate the Body Mass Index?
short answers for big questions
The Body Mass Index is one of the most used criteria so as to know about adult’s state of thinness/normality/obesity. In spite of being widely used, its use is not consensual, since it doesn’t have in mind the influence of racial and ethnic difference. Another big problem concerning the BMI is due to the fact that it doesn’t have in mind people with lots of muscular mass, such is the case of sportsmen and sportswoman.
To calculate the BMI, we use the following formula: `IMC = p/a^2`. We have to notice that `p` stands for weight in Kg and `a` stand for height in metres. After calculating the Index, we use the following table:
| Condition | BMI (Women) | BMI (Men) |
|---|---|---|
| Under the weight | `< 19.1` | `< 20.7` |
| Normal weight | `19.1 - 25.8` | `20.7 - 26.4` |
| Slightly under the weight | `25.8 - 27.3` | `26.4 - 27.8` |
| Above the ideal weight | `27.3 - 32.3` | `27.8 - 31.1` |
| Obese | `> 32.3` | `> 31.1` |
The problem with the BMI is that if you are trying to establish a mathematical relation between two measures of different dimension (Mass and Height). In order to understand the reason for this incompatibility, you have to pay attention to the following: the eight is a linear measure, this is, it is the distance between two specific points: The region of the sole and the highest point of the head. The Body Mass (usually known as weight) is a three-dimensional measure. Mass takes up space, so it has volume. Coming back to the formula, when we square the denominator, we are changing a linear measure into a surface measure as it happens when we want to calculate the area of a land. So, the formula establishes a wrong relation between volume and surface, which are completely different mathematical concepts.
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