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Bioimpedance is a test that analyzes body composition, indicating the approximate amount of muscle, bone and fat. This exam is widely used in gyms and as a complement to nutrition consultations to assess the person's body composition and, thus, indicate the best food and training plan or to evaluate the results.
The bioimpedance test can be performed every 3 or 6 months in order to better compare the results and, thus, verify any evolution of body composition. This test is done on special scales, such as Tanita or Omron, which have metal plates that conduct a weak type of electrical current through the entire body.
So, in addition to the current weight, these scales also show the amount of muscle, fat, water and even the calories the body burns throughout the day, according to gender, age, height and intensity of activity of physics, which are data entered into the balance.
Understand how it works in our fun video:
How it's made
Bioimpedance devices are able to assess the percentage of fat, muscle, bones and water in the body because an electrical current passes through the body through metal plates. This current travels easily through water, so very hydrated tissues, such as muscles, let the current through quickly. On the other hand, fat and bones have little water and, therefore, the current has greater difficulty in passing.
E and thus the difference between the resistance of the fat, in letting the current pass, and the speed with which it passes in tissues such as the muscles, for example, allows the device to calculate the value that indicates the amount of lean mass, fat and water.
So, to know the composition of the body, just go barefoot and without socks on the bioimpedance scale, like Tanita, or and hold a metal plate in front of the body, which can exist in another type of device smaller. The biggest difference between these two bioimpedance methods is that, on the scale, the results are more accurate for the composition of the lower half of the body, while on the device, which is held in the hands, the result refers to the composition of the trunk, arms and legs. head. Therefore, the most accurate way of knowing body composition is to use a scale that combines both methods.
How to ensure accurate results
For the exam to indicate the correct values of fat and lean mass, it is necessary to guarantee some conditions, such as:
- Avoid eating, drinking coffee or exercising in the previous 4 hours;
- Drink 2 to 4 glasses of water 2 hours before the exam.
- Do not drink alcohol in the previous 24 hours;
- Do not apply cream on your feet or hands.
Furthermore, using small, lightweight parts helps to ensure that the results are as accurate as possible.
All preparation is very important because, for example, with regard to water, if there is not adequate hydration, the body has less water for the electric current to flow through and, therefore, the value of fat mass may be bigger than the real one.
Also, when there is fluid retention, it is also important to take the test as soon as possible, and inform the technician, as excess water in the body can lead to an increase in the amount of lean mass, which also does not reflect the reality.
What does the result mean
In addition to weight and Body Mass Index (BMI), the different values offered by bioimpedance devices, or scales, are:
1. Fat mass
The amount of fat mass can be given in % or in Kg, depending on the type of appliance. The recommended values of fat mass vary according to sex and age in percentage, as shown in the table below:
| Age | Men | Women | ||||
| Low | Normal | High | Low | Normal | High | |
| 15 to 24 | < 13, 1 | 13, 2 to 18, 6 | > 18, 7 | < 22, 9 | 23 to 29, 6 | > 29, 7 |
| 25 to 34 | < 15, 2 | 15, 3 to 21, 8 | > 21, 9 | < 22, 8 | 22, 9 to 29, 7 | > 29, 8 |
| 35 to 44 | < 16, 1 | 16, 2 to 23, 1 | > 23, 2 | < 22, 7 | 22, 8 to 29, 8 | > 29, 9 |
| 45 to 54 | < 16, 5 | 16, 6 to 23, 7 | > 23, 8 | < 23, 3 | 23, 4 to 31, 9 | > 32, 0 |
| 55 to 64 | < 17, 7 | 17, 8 to 26, 3 | > 26, 4 | < 28, 3 | 28, 4 to 35, 9 | > 36, 0 |
| 65 to 74 | < 19, 8 | 19, 9 to 27, 5 | > 27, 6 | < 31, 4 | 31, 5 to 39, 8 | > 39, 9 |
| 75 to 84 | < 21, 1 | 21, 2 to 27, 9 | > 28, 0 | < 32, 8 | 32, 9 to 40, 3 | > 40, 4 |
| > 85 | < 25, 9 | 25, 6 to 31, 3 | > 31, 4 | < 31, 2 | 31, 3 to 42, 4 | > 42, 5 |
Ideally, the value of fat mass should be in the range referred to as normal, because when it is above this value it means that you have a lot of fat accumulated, which increases the risk of various diseases, such as obesity or diabetes.
Athletes, on the other hand, usually have a lower than normal fat mass value, see in this table what is the ideal fat mass for their height and weight.
2. Lean mass
The lean mass value indicates the amount of muscle and water in the body, and some more modern scales and appliances already make the difference between the two values. For lean mass, the recommended values in kg are:
| Age | Men | Women | ||||
| Low | Normal | High | Low | Normal | High | |
| 15 to 24 | < 54, 7 | 54, 8 to 62, 3 | > 62, 4 | < 39, 9 | 40, 0 to 44, 9 | > 45, 0 |
| 24 to 34 | < 56, 5 | 56, 6 to 63, 5 | > 63, 6 | < 39, 9 | 40, 0 to 45, 4 | > 45, 5 |
| 35 to 44 | < 56, 3 | 58, 4 to 63, 6 | > 63, 7 | < 40, 0 | 40, 1 to 45, 3 | > 45, 4 |
| 45 to 54 | < 55, 3 | 55, 2 to 61, 5 | > 61, 6 | < 40, 2 | 40, 3 to 45, 6 | > 45, 7 |
| 55 to 64 | < 54, 0 | 54, 1 to 61, 5 | > 61, 6 | < 38, 7 | 38, 8 to 44, 7 | > 44, 8 |
| 65 to 74 | < 53, 2 | 53, 3 to 61, 2 | > 61, 1 | < 38, 4 | 38, 5 to 45, 4 | > 45, 5 |
| 75 to 84 | < 50, 5 | 50, 6 to 58, 1 | > 58, 2 | < 36, 2 | 36, 3 to 42, 1 | > 42, 2 |
| > 85 | < 48, 5 | 48, 6 to 53, 2 | > 53, 3 | < 33, 6 | 33, 7 to 39, 9 | > 40, 0 |
Similar to fat mass, lean mass should also be in the range of values defined as normal, however, athletes generally have higher values due to frequent workouts that facilitate muscle building. People who are sedentary or who don't do weight training at the gym usually have a lower value.
Lean mass is normally used to evaluate the results of a training plan, for example, as it allows you to assess whether you are gaining muscle with the type of exercise you are doing.
3. Muscle mass
Usually, muscle mass should increase throughout bioimpedance assessments, because the greater the amount of muscle, the greater the amount of calories expended per day, which makes it easier to eliminate excess fat from the body and prevent the onset of various cardiovascular diseases. This information can be given in pounds of muscle or percentage.
The amount of muscle mass shows only the weight of the muscles within the lean mass, not counting water and other body tissues, for example. This type of mass also includes the smooth muscles of some organs, such as the stomach or intestine, as well as the heart muscle.
4. Hydration
The reference values for the amount of water in men and women are different and are described below:
- Woman: 45% to 60%;
- Man: 50% to 65%.
This value is very important to know if the organism is well hydrated, what guarantees the he alth of the muscles, avoids cramps, ruptures and injuries, guaranteeing a progressive improvement in the performance and in the results of the training.
Thus, when the value is below the reference range, it is advisable to increase the water intake per day, to about 2 liters, in order to avoid becoming dehydrated.
5. Bone density
The value of bone density, or bone weight, must be constant over time to ensure that bones are he althy and follow the evolution of bone density, which is why it is very important to evaluate the benefits of physical activity in elderly or people with osteopenia or osteoporosis, for example, since regular physical exercise helps to strengthen bones and often treat bone density loss.
Also find out which are the best exercises to strengthen bones and improve bone density in the next bioimpedance exam.
6. Visceral Fat
Visceral fat is the amount of fat that is stored in the abdominal region, around vital organs such as the heart. The value can vary between 1 and 59, being divided into two groups:
- He althy: 1 to 12;
- Harmful: 13 to 59.
Although the presence of visceral fat helps protect organs, excess fat is harmful and can lead to various diseases, such as high blood pressure, diabetes and even heart failure.
7. Basal metabolism rate
Basal metabolism is the amount of calories the body spends to function, and this number is calculated based on the age, sex and physical activity entered on the scale.
Knowing this value is very useful for people who are on a diet to know how much less to eat to lose weight or how many more calories to eat to gain weight.
In addition, the devices can also display the metabolic age which represents the age for which the current metabolism rate is recommended. Thus, the metabolic age must always be equal to or lower than the current age for it to be a positive result for a he althy person.
To increase the rate of metabolism, you must increase the amount of lean mass and this consequently reduces fat mass, as muscle is an active tissue and spends more calories than fat, contributing to increased burning calories from diet or stored body fat.
These scales over time get cheaper and cheaper although the price of a bioimpedance scale is still higher than a conventional scale, it is a very interesting way to keep the shape under surveillance, and the benefits can make up for the money spent.
