Bioelectrical Impedance: What it Measures & Normal Levels

Bioelectrical impedance is a test that looks at body composition. It indicates approximately the amount of muscle, bone and fat you have in the body. This test is often used in gym settings, as well as to complement a nutritional assessment, to ensure a customized eating and training plan. It can also be used to evaluate results of a plan. 

The bioelectrical impedance test is done on a special scale that has metal plates to place your feet on. These plates emit a weak electrical current that travels up the body. 

In addition to reporting current way, a bioelectrical impedance scale can also show the amount of muscle, fat, water and even calories your body burns throughout the day. It takes factors like sex, age, height and physical activity level into consideration. 

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How it works

Bioelectrical impedance equipment can look at the percentage of fat, muscle, bones and water in the body. It sends a weak electrical current into the body through the soles of the feet. This current travels easily through water, therefore hydrated tissue like muscles, allow for a faster current. Fat and bones contain less water, on the other hand, and the current has more difficulty traveling through these tissues.

This scale determines lean muscle, fat and water levels by calculating how quickly the electrical current flows through different tissues.

To know your body fat composition, simply step on a bioelectrical impedance while barefoot, or hold a hand-held scale in your hands away from your body. The biggest difference between these two pieces of equipment is that the scale tends to be more accurate in reporting lower body composition, while the hand-held scale is best for upper body composition. There are scales that combine both methods, which is the most accurate type of scale to use.

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:  

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, 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: 

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

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 cardiovasclar disease. This result can be reported in kilgrams 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 refernece 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 scalres and interesting way to monitor your fitness and its benefits can compensate for the money invested into one.