Bioelectrical impedance is a technique used to estimate body composition by measuring how an electrical signal moves through the body. Since fat, muscle, and water conduct electricity differently, the results can give insight into the body's internal makeup.
This method is widely used in health, fitness, and clinical settings because it is quick, noninvasive, and affordable. Devices range from simple bathroom scales to advanced medical equipment, making the technology accessible for both personal and professional use.
Bioelectrical impedance can provide measurements such as body fat percentage, muscle mass, and total body water. These values are important for tracking progress, guiding nutrition plans, and supporting overall health assessments.
What it's used for
Bioelectrical impedance is a method used to measure body composition, including muscle mass, body fat, total body water, and other internal components.
This technique is useful for assessing nutritional status and identifying the risk of chronic conditions related to excess weight or obesity.
It is also used to track changes in body composition over time, such as during weight loss programs, physical training, or rehabilitation.
In addition, bioelectrical impedance helps evaluate hydration levels, which is especially important for athletes, older adults, and people with certain medical conditions.
How it works
Bioelectrical impedance works differently depending on the type of device used:
- Devices measuring the upper or lower body: The person either stands on metal footplates or holds metal hand sensors.
- Whole-body analysis devices: The person lies on their back while four electrodes are placed on the hands and feet.
- Advanced segmental devices: The person stands on foot sensors and holds handles at the same time, allowing the machine to assess arms, legs, and torso separately.
During the test, a low electrical current passes through the body via metal sensors. Because the current moves more easily through water, tissues with higher water content—like muscles—allow faster electrical flow.
In contrast, fat and bone contain less water and slow the current down.
By analyzing how the current travels through different tissues, the device calculates estimates for lean mass, fat mass, and body water.
How to ensure accurate results
To obtain exact body composition results, you should consider the following:
- Avoid eating, drinking coffee or exercising at least 4 hours before the reading
- Drink 2 to 4 cups of water 2 hours before the reading
- Do not drink any alcohol 24 hours before the reading
- Do not apply cream to your hands or feet
You should use small, light clothing to ensure your results are as accurate as possible.
All of these considerations are very important, as even your current hydration status, for example, can affect the results.
If you experience water retention, it is important to complete this test as early on in the day as possible, as excess water and lead to an inaccurate muscle percentage that does not reflect reality.
What it measures
In addition to your weight and BMI, a bioelectrical impedance scale can report different values like:
1. Fat tissue
Fat can be reported as a percentage or in kg, depending on the scale. The recommended fat percentages depending on age and height are as follows:
Ideally, your body fat percentage should be within the normal range, as increased fat levels can increase your risk for various diseases, like obesity or diabetes. Athletes will normally have a lower fat percentage.
2. Lean tissue
Your lean tissue refers to your levels of muscle and water, although some scales report individual values for each. For your lean mass, the recommended levels in kg are:
Similarly to fat compositions, your lean mas should be within a normal range (although athletes will generally present with higher levels due to frequent training that promotes muscle building). Sedentary people or people who do not regularly engage in resistance training will usually have a lower result.
Lean mass results is used to evaluate the results of an exercise regimen to determine if it has been effective in achieving fitness goals.
3. Muscle mass
Normally, muscle mass will increase after a significant amount of time has been dedicated to resistance training. A higher muscle mass will mean more calories burned in the day, which help to burn excess fat and prevent cardiovascular disease. This result can be reported in kilograms or as a percentage.
The quantity of muscle mass indicates the muscle weight within the lean tissue (without water or other body tissues). This type of tissue also takes lean muscle from other organs into consideration, like stomach, intestinal and cardiac muscles.
4. Hydration
Reference values for water levels in men and women are as follows:
- Women: 45% to 60%
- Men: 50% to 65%
This value is very beneficial for knowing the body’s hydration status. Adequate water intake is important for muscular health and can prevent cramps, muscle injuries and a progressive performance with results in the gym.
Water levels below the reference ranges should be addressed by increasing water intake (aiming for about 2 L per day).
5. Bone density
Bone density should be evaluated over time to ensure bones remain healthy. This is especially important in older adults or people with osteopenia and osteoporosis. These populations can especially benefit from regular exercise, as it can strengthen the bones and prevent further bone loss.
6. Visceral fat
Visceral fat is the amount of fat that is stores in the abdominal region, around the vital organs (like the heart). Values are reported within a range of 1 to 59, with results divided into two groups:
- Healthy: 1 to 12
- Health risk: 13 to 59
Although visceral fat helps to protect the organs, excess fat can be unhealthy and is associated with several health conditions like high blood pressure, diabetes and cardiac failure.
7. Basal metabolic rate
Basal metabolic rate is the amount of calories that body burns to carry out normal functions. It is calculated using age, sex and physical activity level, which are entered into the scale.
Knowing this value is very important for people on a diet, to know whether they need to eat more or less to achieve their fitness goals.
In addition, these scales can also indicate your metabolic age, which represents the age for which your current metabolic rate is recommended. Your metabolic age should be equal to or less than your actual age to ensure optimal health.
To increase your basal metabolic rate, you should increase your lean mass, which will consequently decrease your fat mass (as muscle is a tissue that burns more energy than fat).
These scales are widely available, and although current prices are more accessible these days, they tend to be more expensive than conventional scales. Nonetheless, bioelectrical impedence scales and interesting way to monitor your fitness and its benefits can compensate for the money invested into one.