Measuring Body Composition

Body Composition

Body composition is the ‘relative amount of fat and fat free mass in the body’. It is the physiological make-up of an individual and includes the amount of fat they have in their body and their ‘fat free mass’ which is everything else, including the amount of muscle tissue, bone and other tissues. It is difficult to give recommendations for body fat percentages for different sports performers because what is acceptable or advisable is not recommended for another activity. For example, a sumo wrestler is unlikely to be successful wind surfing and a wind surfer is unlikely to win many sumo contests.

Excess body fat can lead to health problems such as cardiovascular disease and for untrained or sedentary individuals the recommended body fat percentages for health are between 12–20% for males and 17–25% for females.

There are different methods for measuring body composition. It can be a difficult component to measure because internal or visceral fat can only be measured by using expensive CT, DEXA or MRI scanners. DEXA is considered to be the ‘gold standard’ for body composition measuring although this equipment was first designed for measuring bone mineral density. It was quickly realised that the results could be used to accurately measure this fitness component. Previously, underwater weighing was considered the best method to measure body composition.

Body Mass Index (BMI) is frequently used as a measure of physical health and is a simple calculation that uses height and weight to assess whether a person is underweight or overweight. It is used in many countries as a method to indicate whether a person is healthy or not. It is fairly conclusive that having a high body fat percentage severely increases the risks of developing cardiovascular disease. Nonetheless, there is a problem with the ‘obesity’ definition when using the BMI formula to classify individuals as obese. For this reason BMI should only be used as a measure of healthiness in sedentary individuals. Alternative methods are used in combination to BMI results by doctors and health practitioners. This includes; blood lipid profiles and cholesterol testing, waist girth (in men), waist-to-hip girth and body fat percentages. This is particularly apparent for predicting ‘health’ in athletic populations.

Strengths and Limitations of BMI

Using BMI as a calculation has the following advantages:

• It is a reliable measure, i.e. the measure will not change much between days.
• Measuring height and weight is quick and requires no special equipment or expertise
• BMI is a good indicator of health risk in sedentary individuals.

The major limitations of using BMI as a measure of health are:

• The test fails to differentiate between fat and muscle so many muscular athletes are measured as ‘obese’ when in fact they do not have a high body fat percentage. Therefore the use of BMI in athletes is not recommended because it is not a valid indicator of body fat percentage
• The reliability of the measure could be influenced by prior eating or being dehydrated, however, this is not usually a major problem
• The issues created by labelling people as ‘obese’. For example, labelling someone as obese may lead to depression, lowering of self-esteem and can result in eating disorders. Obese individuals are more likely to commit suicide so health professionals must take care when labelling someone with this tag.

BMI is calculated by dividing weight (in kgs) by height (in cm) squared. Obese is defined as having a BMI over 30.

With regards to measuring body fat using skin-fold calipers, in the past, skin-fold measures were taken and used to calculate a ‘body fat percentage’ using prediction equations e.g. ‘20% of your body weight is fat’. However, many researchers have questioned the accuracy of this, especially as many of the equations were developed using white subjects and different races lay down fat in different regions. For this reason, most studies now use the ‘Sum of skin-folds’, which is basically adding together the skin-folds taken at various sites in the body. Unfortunately different researchers use different amounts of measurement sites so this sometimes makes it hard to compare results. There are also a limited number of studies completed to give recommendations for many sports.

Equipment

Skin-fold calipers

Set up

Mark the measurement sites on the performer’s body.

Protocols

• Hold the skin-fold and place the caliper over it.
• Do not pinch the skin too hard.
• Release the calipers slowly until the entire force is on the skin approximately 1 cm in.
• The calipers will pinch the skin and the measurement will decrease as the fat is compressed so take the reading after 1 second.
• Repeat all measurement twice and calculate a mean of the two measures.
• Add together the measurements to calculate the sum of skin-folds.

Strengths of skin-fold testing:

• In ‘experts’ or well-trained individuals reliability is very good and measurements are as accurate as underwater weighing,

• Easy to use once skill has been mastered,

• Does not require much time (20 mins for 8 sites),

• Depending on sites measured this can be a non-invasive method, and

• Relatively inexpensive way of estimating percent body fat.

Limitations of skin-fold testing:

• Accuracy of person measuring can reduce reliability considerably. Poor reliability in untrained testers,

• Potential problems with validity because internal or visceral fat is not measured,

• Validity an issue if person ‘pinches’ muscle as well as fat or only pinches skin,

• May not be an ideal measurement for those who are obese and very lean due to reliability issues,

• Some people do not like being touched,

• may need to be done in private if individual needs to remove tee-shirt,

• With younger participants a ‘chaperone’ may be needed, and

• If calculations are used to estimate body fat percentage then they may not be accurate for people of different populations (e.g. asian, caucasians).