The density of the human body is an important characteristic of the he alth 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 take a closer look at this issue in the article.
Density as a physical quantity
In physics, density is understood as a coefficient that connects the mass and volume of a body into a single equality. The formula for this quantity is: 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 is in cubic meters, the density units will be kg/m3 or g/cm3.
Average human body density and he alth
Before we move on to the consideration of human density, it must be recalled that our body consists of the following basic tissues:
- fatty;
- muscular;
- bone.
Each of themcontains water. The least liquid is found in the bones, then in adipose tissue. Muscles contain the most water. If you subtract the weight of adipose tissue from the total mass of a person, you get a figure that is commonly called lean body mass.
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/cm3, this the dry weight value was found to be 1.100 g/cm3. However, later studies have shown that dry mass density actually varies between 1.082 g/cm3 to 1.113 g/cm3.
What does this data say? It's simple, the lower the average density of a person, the more fat his body contains, which means the higher the risk of cardiovascular disease.
Specific figure for density
It is difficult to give a specific value of the density value, by which we can say that it is normal. This is due to a huge number of factors influencing its value. Here one 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 of 1070 kg/m3. Others say that its minimum values are 930-940 kg/m3. Such a spread of values is associated with one simplefact: the density of a person can decrease significantly if he fills his lungs with air. Thus, the density of a human body of 1070 kg/m3 indicates that he has completely exhaled air from his lungs, on the contrary, the value of 930 kg/m3 obtained with a full breath.
How is human density calculated?
As mentioned above, for this you should measure the mass and volume of the body. There are no problems with the mass, you just need to stand on the scales and immediately get the exact value in kilograms. Volume measurement is more complicated.
The volume of a body of absolutely any complex shape can be accurately determined if it is immersed in a liquid, for example, in water. Then the amount of liquid displaced by a completely immersed 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 the weight of air 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 human swimming ability
As noted above, if a person takes a deep breath, then his average density drops below 1 g/cm3. In turn, it follows from the law of Archimedes that if the average density of a 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/cm3, so if a person fills his lungs with air, he will neverwon't drown. Note that sea water contains a large amount of s alts, which increase its density. In some cases, this increase exceeds the value of 1070 kg/m3, so a person can lie in such water without fear of drowning even with a full exhalation. A striking example is the Dead Sea, the density of water in it is 1240 kg/m3.
It is also curious to consider the question 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 thin material (0.901 g/cm3), which means that the fair sex can float more easily than men.
Average density of a man and a woman: calculation
The above values indicate that when exhaling, the average density of the human body is 1070 kg/m3. However, this value is not specified for women and men. In this paragraph of the article, we will try to get it for each gender, based on the figures above. Also consider that in a he althy state, the percentage of body fat in a man is 15.5%, and for a woman this figure is 22.5% (these values are averages for the corresponding normal limits).
Let's get the formula for the average density first. Let the mass of a human body be m kg, then the mass of fat in it will be equal to pm, and the dry mass is equal to (1-p)m, where p is the percentage of adipose tissue. The volume of the human body issum of fat and dry mass. Considering the formula given at the beginning of the article, we get: V=pm/ρ1 + (1-p)m/ρ2, where ρ1 and ρ2 are fat and dry mass densities, respectively. Now we can calculate the average density of the whole body, we have: ρ=m/(pm/ρ1 + (1-p)m/ρ2)=1/(p/ρ1 + (1-p)/ρ2).
Given that ρ1=0.901 g/cm3 and ρ2=1.1 g/cm3 (the values are given above in the article), then substituting the percentage of body fat for men and women, we get:
- for men: ρ=1/(0, 155/0, 901 + (1-0, 155)/1, 1)=1, 064 g/cm3or 1064 kg/cm3;
- for women: ρ=1/(0.225/0.901 + (1-0.225)/1.1)=1.048 g/cm3or 1048 kg/cm3.
The calculated values are close to 1070 kg/m3. Each person, knowing the percentage of body fat in his body, can use the above formula to calculate his own average body density. Recall that this value corresponds to the state when the person made the maximum exhalation.
