The density of the human body is an important characteristic of the health of the body, so it is useful to know how to calculate it. Moreover, this value is of fundamental importance in some sports. Let's consider this question in more detail in the article.
Density as a physical quantity
In physics, density is understood as a coefficient linking mass and volume of a body into a single equality. The formula for this quantity has the form: ρ = m / V. That is, it can be calculated if you know exactly the mass of the measured object and the volume that it occupies in space.
Since mass is measured in kilograms and volume in cubic meters, the units of density will be kg / m 3 or g / cm 3 .
The average density of the human body and health
Before proceeding to the consideration of human density, it is necessary to recall that our body consists of the following main tissues:
Each of them contains water. The least fluid is in the bones, then in the adipose tissue. Muscle contains the most water. If we subtract the weight of adipose tissue from the total mass of a person, we get a figure, which is usually called dry body weight.
In the 60s of the last century, as a result of studying the dried human corpses of three white people, scientists found that their average fat density was 0.901 g / cm 3 , this value for the dry mass was 1,100 g / cm 3 . However, more recent studies have shown that the dry mass density actually varies between 1.082 g / cm 3 and 1.113 g / cm 3 .
What is this data talking about? Everything is simple, the lower the average density of a person, the more fat is contained in his body, which means that the higher the risks of cardiovascular diseases.
Specific figure for density
It is difficult to give a specific value of the density value by which it can be said that it is normal. This is due to a huge number of factors affecting its importance. It should take into account the mineral composition of the bone, muscle mass, weight of adipose tissue, the values of which vary depending on age, gender and individual characteristics of the body.
Nevertheless, some data collected from a number of literary sources can be cited. Some of them give a figure for the average density of the human body 1070 kg / m3. Others say that its minimum values are 930-940 kg / m 3 . This scatter of values is associated with one simple fact: a person’s density can decrease significantly if he fills his lungs with air. So, the density of the human body 1070 kg / m 3 indicates that he completely exhaled air from the lungs, on the contrary, the value of 930 kg / m 3 is obtained with a full breath.
How is human density calculated?
As mentioned above, for this you need to measure body weight and volume. There are no problems with the mass, just stand on the scales and immediately get the exact value in kilograms. Volume measurement is more complicated.
The body volume of absolutely any complex shape can be precisely determined by immersing it in a liquid, for example, in water. Then the amount of fluid that has displaced a completely submerged body will be exactly equal to the desired indicator. This property is used to determine the volume of a person who is seated on a special chair, asked to exhale weight from the lungs, and then immersed in water. By measuring its weight under water, you can get the appropriate figure to determine the desired indicator.
Density and swimming ability of a person
As noted above, if a person takes a deep breath, then his average density drops below 1 g / cm 3 . In turn, from the law of Archimedes it follows that if the average density of the body exceeds this value for the liquid in which it is located, then this body will inevitably sink. The density of fresh water is 1 g / cm 3 , so if a person fills his lungs with air, he will never drown. Note that sea water contains a large amount of salts, which increase its density. In some cases, this increase exceeds the value of 1070 kg / m 3 , so a person can lie in such water, not afraid to drown even with a full exhalation. A vivid example is the Dead Sea, the density of water in it is 1240 kg / m 3 .
It is also curious to consider the issue of this item from the point of view of a person’s gender. The female body on average contains more adipose tissue than the male. Fat is a relatively loose matter (0.901 g / cm 3 ), which means that it is easier for women to stay on water than men.
The average density of men and women: calculation
The above values indicate that when you exhale, the average density of the human body is 1070 kg / m 3 . However, this value is not indicated for women and men. In this paragraph of the article, we will try to obtain it for each sex, based on the above figures. We also take into account that in a healthy state the percentage of fat in a man’s body is 15.5%, while for a woman this figure is 22.5% (these values are average for the corresponding normal limits).
First we get the formula for the average density. Let the human body weight be m kg, then the mass of fat in it will be equal to p * m, and the dry mass will be equal to (1-p) * m, where p is the percentage of adipose tissue. The human body volume is equal to the sum of the volumes of fat and dry weight. Given the formula given at the beginning of the article, we obtain: V = p * m / ρ 1 + (1-p) * m / ρ 2 , here ρ 1 and ρ 2 are the densities for fat and dry mass, respectively. Now we can calculate the average density of the whole body, we have: ρ = m / (p * m / ρ 1 + (1-p) * m / ρ 2 ) = 1 / (p / ρ 1 + (1-p) / ρ 2 )
Given that ρ 1 = 0.901 g / cm 3 and ρ 2 = 1.1 g / cm 3 (the values are given above in the article), then substituting the percentage of fat for men and women, we get:
- for men: ρ = 1 / (0.155 / 0.901 + (1-0.155) / 1.1) = 1.064 g / cm 3 or 1064 kg / cm 3 ;
- for women: ρ = 1 / (0.225 / 0.901 + (1-0.225) / 1.1) = 1.048 g / cm 3 or 1048 kg / cm 3 .
The calculated values are close to the number 1070 kg / m 3 . Everyone, knowing the percentage of fat in their body, can use the above formula to calculate their own average body density. Recall that this value corresponds to the state when the person exhaled maximally.