ISSA SN Chapter 14: Body Composition

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Chapter Goals

  • Describe and define the terms that relate to the composition of the body.
  • Discuss the body composition approaches to measurement.
  • Determine someone’s body composition. 


Trainers and athletes need to be well-informed regarding their bodies, as opposed to what the bathroom scales and the height and weight charts give. The amounts of lean body weight and fat that the body is made up of are vital for athletes. The information to be provided by this will involve the metabolism, caloric needs, and some other factors. 

Body Composition Assessment

This will be a major part of your initial assessment procedure with new athlete clients and important ongoing evaluative tests with clients you see often. 

Excess body fat levels are associated with cardiovascular diseases, cancers, and some other maladies. Body composition assessment is a crucial source for motivating clients, as seen in the positive changes in overall fitness levels. 

We have many methods out there for determining the levels of body fat that people have. Skinfold calipers are a popular device for skinfold calculations. These are special calipers used to measure skinfold thickness in specific spots.

Methods of Body Composition Determination

Underwater weighing is a widely used technique, also called hydrostatic weighing. Weight comparison is done by looking at the weight of your body in the air and then the weight when fully submerged in water after completely exhaling. The body’s density is then found while the method considers fat less dense than water. Someone with high levels of fat will weigh less than someone with a similar weight and less fat. Corrections are made based on the amount of air in the lungs after exhaling.

Air Displacement Plethysmograph is known as the BOD POD. It is the gold standard that exists for finding body composition. This uses air displacement to find whole body densitometry and determine the body composition. A full test of this will require five minutes of time and will give fast, highly accurate, safe, and comfortable results. 

Bioelectrical impedance is the approach made on a basis of water conducting electricity better than fat. Since muscle has higher levels of water, and fat low levels, the rate of electricity conduction is used to estimate the body composition on those two facts. Many devices have been made with this science. There are easy to use versions you hold in your hand, and there are more popular scales that do this. Dehydration might alter the results you receive with these methods. 

Dual Energy X-Ray Absorptiometry is a very sophisticated way that uses DEXA machines to find body composition. It uses a three compartment model to differentiate the body into bone, fat tissues, and lean soft tissue. It is an expensive method that needs a very qualified radiologist.

B-mode ultrasound uses ultrasound technology to determine the levels of subcutaneous body fat measures as an alternative to using skinfold calipers. The use of brightness mode has been seen to be valid and reliable for estimating body fat. The acoustic waves sent by the transducer will display images that can determine everything. 

Skinfold Caliper is the device discussed slightly a little earlier. Since some body fat is under the skin, it follows that the thicker folds someone has, the fatter the person is. The calipers are specially designed for this process. The measurements from the locations on the body are put into equations for finding the body’s density. 

How to Use the Fat-O-Meter Skinfold Caliper

Before predicting clients’ body composition, you should know some about getting the best results. 

Allow a  lot of time for practice with the calipers, taking measures one at a time at the sites in an order of rotation. Check the test reliability after these are taken. 

Be careful finding the sites for measures by using the right landmarks described for the sites.

Check the caliper jaw pressure to know if no damage has happened to the spring. The pressure should be 10g/mm2. 

Measure the sites in an order with rotation. Take them one at a time, check those sites 2 – 3 times each, and use their average. 

Select the most valid equation for predictions. 

This is a two handed operation and it requires skill on the testers’ part. You take hold of the skin and the subcutaneous fat in the left thumb and the forefinger or middle finger. You then grab the caliper with your right hand and face the scale toward you. When your thumb is on the serrated part of the calipers, slide it open, and put the caliper on the appropriate skinfold site. Let it close around the fold and take the reading in mm to the nearest half mm. 

Things to watch out for when measuring

  • Do so directly on the skin and not through any clothing. The readings must be taken while standing and on the right side of the body. 
  • Take the readings two to three times in the rotation and average them out for use in the right equation.
  • Practice A Lot!!!

Generalized Adult Equations to Determine Percent Body Fat Most Accurately

  • Many equations are available depending on the general population and the specific subgroups. 

Common Skinfold Sites

  • Subscapular, triceps, suprailium, thigh, chest, and abdomen. 

Percentage of Body Fat?

This is an estimate of the percentage of the body that is made up of fat. Normal values for body fat percent are somewhat reported to report. Too low body fat can be a problem. For men, this is a percentage in the range of 5 – 10%. This is seen as a range between 10 – 15% for females. 

Body Mass Index (BMI)

This is useful for the general population, but it begins to have more limitations when it comes to athletes. This is due to the higher than average muscle mass present in athletes, and it is not considered with BMI. 

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What is BMI?

BMI is a measure of your weight relative to your height. It is used to see if someone is underweight, normal, overweight, or even obese based on the population. The person’s weight is found in kilograms and divided by the square of height in meters. It does not actually measure the person’s body fat, but it is shown to correlate slightly with measures of body fat found in skinfold thickness measures. 

How is BMI used?

High BMIs are indicators of high amounts of fat in the body.

For us to determine if BMI is a risk for health, further assessments are needed by the health providers. These may include skinfold measures, physical activity, and family histories. 

What are the BMI trends for adults in the United States?

The prevalence of BMIs in adults higher than 30 has greatly increased ever since the 70s. 

Why is BMI used to measure overweight and obesity?

It can be used for population assessment of overweight and obesity prevalence. BMI is inexpensive to do and easy for clinicians to use. It is not diagnostic.

What are some of the other ways to assess excess body fat besides BMI?

This includes the ways discussed at the beginning of the chapter. 

How is BMI interpreted for adults?

The following are associated with BMI ranges:

  • Under 18.5 is equal to being underweight status.
  • 18.5 – 24.9 is equal to a normal or healthy weight.
  • 25 – 29.9 is equal to overweight status.
  • 30 and higher is going to be equal to obese status.

How good is BMI as an indicator of body fatness?

The correlation between the two is somewhat strong, but the body fat levels of people will still differ somewhat when they have similar weights. 

Some general notes

When people have the same BMI, women will have more body fat than men. 

At the same BMI, black people have less body fat than whites, and Asians have more body fat than whites do.

When at the same BMI, older people will have more body fat than someone who is at a younger age. 

At the same BMI, athletes have less body fat than people that are not athletes.

The accuracy and indications of body fatness are higher in people with greater BMI and body fat levels. Relatively high body fat or a lean body mass can relate to higher BMIs. 

It is often that we see actual healthy athletes receive a BMI that is considered unhealthy when in reality, it is simply the higher levels of lean muscle mass and the fact BMI does not take that into consideration. 

What are the health consequences of obesity for adults?

There is an increased risk for all of the following:

  • All causes of mortality
  • High blood pressures
  • High cholesterol 
  • Type 2 diabetes
  • Coronary heart disease
  • Stroke
  • Gallbladder disease
  • Osteoarthritis
  • Sleep apnea and problems with breathing
  • Chronic inflammation and increases in stress from oxidation
  • Some cancer
  • Low quality of life
  • Mental illnesses like depression, anxiety, and other mental disorders

Body Types

How your body looks is a result of genetics and factors of the environment like your nutrition and training. The factor of genetics has the most dominant influence on the structure of the body, both inside and out. Humans can be three different types of bodies.

Mesomorphic or muscular body types

Ectomorphic or slime and linear body types

Endomorphic or fat and round body types

The Sheldon system uses 3 digits to classify body types on a scale. This refers to the degrees of body types. The first refers to the degree of endomorph, the next digit Is the degree of mesomorph, and the last digit will be the degree of ectomorph. This system allows us to understand genetic dispositions better.

ISSA SN Chapter 14: Body Composition 4
ISSA SN Chapter 14: Body Composition 5
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Tyler Read - Certified Personal Trainer with PTPioneer

Tyler Read

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