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Body Composition

At its most basic level, body composition refers to the amount of fat, muscle and bone mass that make up your total body weight. Measuring body composition can range from the very simple, like the standard Body Mass Index (BMI) chart, to very complex, like using Dual Energy X-Ray Absorptiometry (DEXA) imaging. Below, I’ll explain a few methods along with the pros and cons of each.

Body Mass Index
BMI is easily the most convenient and widely used method to measure body composition. To calculate your BMI and learn more about it, visit this website.

Although BMI does not directly measure your composition, it does provide you with a score, based on the ratio of your height to weight, to assess your health. A score under 18.5 is considered underweight, between 18.5 to 24.9 is considered normal, 25 to 29.9 is overweight, while anything above 30 is considered obese.

However, these numbers don’t tell the whole story. For example, I stand at 5’11” and weigh 190 lbs, which puts me at a 26.5, the overweight category. As an avid exerciser and weight lifter, I certainly don’t consider myself overweight. This is an area in which the BMI is limited, since it doesn’t take into account the ratio of fat and lean mass in its measurement. Even though I’m considered overweight, much of that weight is made up of lean muscle mass. This is a common problem for men with lots of muscle mass due to weight training. 

The issue runs the other way as well. Let’s take a man with the same height as mine, but who only weighs 160 lbs and never exercises. Even though his BMI comes in at 22.3 –well within the normal range– it doesn’t necessarily mean he is healthier. People who are inactive are more likely to have a higher ratio of fat to muscle mass. So even though they weigh less, it is possible for them to be at greater risk for future health problems related to their inactivity.

Skin Fold Calipers
Another common technique used in many gyms and research studies is using skin fold calipers to physically assess a person’s percentage of body fat. This method involves using calipers to pinch certain areas of the body. From the measurements obtained, the numbers are then plugged into a formula that determines a person’s percentage of body fat. It’s quick, easy to administer and cheap to do, but what it provides in convenience it lacks in accuracy.

The score depends entirely upon the skill of the technician taking the measurements, which can vary widely between people. The skin fold measurement has a  +/- 3% to 4%. Measurement must be taken very precisely, and, like any skill, it takes practice to become proficient at it. If you have been measured via skin fold calipers, try to have the same person take the measurements each time to ensure validity between measurements.

Bioelectrical Impedance (BIA)
BIA is a method of measuring composition that passes a small, harmless electrical current through the body. A percentage of body fat is given based on how much resistance the current faces as it passes through body tissues. It moves more quickly through tissues that are made primarily of water, like blood and muscle, and encounter more resistance when passing through fat and bone.

Today’s home use BIA devices are handheld units that are quick and painless to use. The user enters some basic data, like their height, weight, gender, age and how physically active they are. After this information is entered, the current is passed through the body and a percentage of body fat is given. You can buy a BIA unit for around $35, so expense also isn’t a limiting factor.

However, it still isn’t perfect. This method also has +/- 3% to 4% but can be even greater. Since water is a major factor in determining a person’s score, hydration is also a huge factor. Someone who is dehydrated may have an overestimated percentage. You should never measure yourself after a workout, since your score will not be very accurate. If you do choose to use BIA, try to measure yourself in a consistent manner. For example, try to measure at the same time of day, and maintain a consistent hydration level across each measurement.

This is by far the most accurate way to assess composition, but it’s also the most expensive and impractical. DEXA uses a low grade x-ray to scan the body and reveal the amount of fat, muscle and bone mass very precisely. DEXA is also used to examine a person’s bone mineral density, and it is recommended that women over the age of 65 get scanned anyway to assess their risk of osteoporosis, so this method would take care of both. The major downside is cost, but as DEXA becomes more popular and commonplace, the costs are coming down. There are even businesses who now offer DEXA scans specifically for body composition.


As you can see, there are many different methods to measure body composition, each with their pros and cons. It is important to remember that no method is perfect and that numbers obtained via skin fold and BIA are subject to lots or variability.

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