Understanding Body Mass Index (BMI) and Body Composition

Posted on Aug 26, 2024 in Physical Education

Body Mass Index (BMI)

Body mass index (BMI) is a measure of body fat based on your weight in relation to your height and applies to most adult men and women aged 20 and over. For children aged 2 and over, BMI percentile is the best assessment of body fat.

BMI does not measure body fat directly. However, research indicates that BMI correlates to direct measures of body fat, such as underwater weighing and dual-energy X-ray absorptiometry (DXA), and is considered an inexpensive and easy-to-perform alternative for these.

BMI is not accurate enough to be used as a diagnostic tool. However, it is used as a screening tool to identify potential weight problems in adults.

A person may have a high BMI. Yet, to determine if this excess weight is a health risk, a health care provider would need to complete further assessments, such as:

• Skinfold thickness measurements
• Evaluations of diet
• Physical activity
• Family history
• Other appropriate health screenings

How to Calculate BMI for Adults

Belgium Statistician Adolphe Quetelet developed the BMI formula approximately 150 years ago.

The calculation of BMI is based on the following formulas:

Metric BMI Formula

Weight (kg) / Height (m)²

Precautions during measurements:

1. The body weight must be taken on a reliable and perfect weighing machine.
2. While taking body weight, one must wear minimum required clothes.
3. While measuring height, one should be bare-footed, and his/her body should be in a straight position.

Waist-Hip Ratio

Spare body fat is stored under our skin and around the abdomen’s organs. Doctors know that fat stored around the tummy has more health consequences and is more likely to cause heart disease than fat on the thighs or bottom. People with more tummy fat are called apple shapes, and those with more thigh and bottom fat are pear shapes.

What’s your waist-to-hip ratio?

Measure your waist: Stand up, relax, then measure the narrowest part of your abdomen, usually around your belly button.

Measure your hips: Still standing, measure the largest part around your hips, usually just below your bottom cheeks.

Remember: Don’t pull the tape tight around your waist and hips, or you won’t get a proper reading.

A ratio over 1.0 for men or over 0.85 for women suggests there’s more weight around your middle than is ideal, which can cause health problems. Increasing your activity and modifying your diet will help reduce your waist-hip ratio while also benefiting your health in other ways. Moving more makes your heart, lungs, and circulation stronger and gives you more energy.

Hippocrates’ Four Temperaments

Hippocrates was a famous physician of Greece. He classified individuals into four main groups:

Sanguine

The sanguine temperament is traditionally associated with air. People with this temperament tend to be lively, sociable, carefree, talkative, and pleasure-seeking. They may be warm-hearted and optimistic. They can make new friends easily, be imaginative and artistic, and often have many ideas. They can be flighty and changeable; thus, sanguine personalities may struggle with following tasks all the way through and be chronically late or forgetful.

Choleric

The choleric temperament is traditionally associated with fire. People with this temperament tend to be egocentric and extroverted. They may be excitable, impulsive, and restless, with reserves of aggression, energy, and/or passion and try to instill that in others. They tend to be task-oriented people and are focused on getting a job done efficiently; their motto is usually “do it now.” They can be ambitious, strong-willed, and like to be in charge. They can show leadership, are good at planning, and are often practical and solution-oriented.

Melancholic

The melancholic temperament is traditionally associated with the element of earth. People with this temperament may appear serious, introverted, cautious, or even suspicious. They can become preoccupied with the tragedy and cruelty in the world and are susceptible to depression and moodiness. They may be focused and conscientious. They often prefer to do things themselves, both to meet their own standards and because they are not inherently sociable.

Phlegmatic

The phlegmatic temperament is traditionally associated with water. People with this temperament may be inward and private, thoughtful, reasonable, calm, patient, caring, and tolerant. They tend to have a rich inner life, seek a quiet, peaceful atmosphere, and be content with themselves. They tend to be steadfast, consistent in their habits, and thus steady and faithful friends.

Ernest Kretschmer’s Body Types

^{Ernest Kretschmer}

a. Pyknic type:

These are people who are short and have a round body. They will have personality traits of extroverts. These people are more prone to suffer from a mental disorder called Manic Depressive Psychosis (MDP).

b. Asthenic type:

These people will have a slender or slim body. They will have the personality traits of introverts. These people are more prone to suffer from a serious mental disorder called Schizophrenia.

c. Athletic type:

These people will have a strong body. They are more energetic and aggressive. They will be strong enough, determined, adventurous, and balanced. They are comparable with ambiverts. They are more prone to suffer from MDP.

Somatotypes

Ectomorphic

An ectomorph is the complete opposite of the Endomorph. Physically, they have narrow shoulders, thin legs and arms, little fat on the body, a narrow face, and a narrow chest. They may eat just as much as the endomorph but never seem to gain any weight. They always stay skinny. Personality-wise, they tend to be self-conscious, socially anxious, artistic, thoughtful, quiet, and private. They always keep to themselves and are afraid to branch out.

Mesomorphic

The mesomorph is in between the endomorph and the thin ectomorph. They have an attractive and desirable body. Physically, they tend to have a large head and broad shoulders with a narrow waist. They have a strong muscular body and strong arms and legs and little fat on the body. They work for the body they have so that they could have an attractive body. Psychologically, the mesomorph is adventurous and courageous. They are not afraid to break out and do new things with new people.

Endomorphic

An Endomorphic somatotype is also known as a viscerotonic. The characteristic traits of this somatotype usually include being relaxed, tolerant, comfortable, and sociable. Psychologically, they are also fun-loving, good-humored, even-tempered, and they love food and affection. The Endomorph is physically “round.” They have wide hips and narrow shoulders that give a pear-shape. They tend to have a lot of extra fat on their body and on their arms and thighs. They have skinny ankles and wrists that make the rest of their body look even bigger.

Somatotype Measurement

Somatotype is most commonly measured using the Heath-Carter measurement system, in which ratings for endomorphy, mesomorphy, and ectomorphy are calculated using various anthropometrical measurements and also sometimes in conjunction with standardized photos (photoscopic method).

In each of the three categories, someone is generally classified on a scale from 1 to 7 (though higher ratings are possible), though you cannot score highly on all three. The three numbers together give a somatotype number, with the endomorphy score first, then mesomorphy, and finally ectomorphy (e.g., 1-5-2). The scores may also be plotted in a shield diagram or somatograph, representing the somatotype on a two-dimensional scale.

Measuring Height and Weight

Measure Height

Remove the child or teen’s shoes, bulky clothing, and hair ornaments and unbraid hair that interferes with the measurement.

Take the height measurement on flooring that is not carpeted and against a flat surface such as a wall with no molding.

Have the child or teen stand with feet flat, together, and against the wall. Make sure legs are straight, arms are at sides, and shoulders are level.

Make sure the child or teen is looking straight ahead and that the line of sight is parallel with the floor.

Take the measurement while the child or teen stands with head, shoulders, buttocks, and heels touching the flat surface (wall). (See illustration.) Depending on the overall body shape of the child or teen, all points may not touch the wall.

Use a flat headpiece to form a right angle with the wall and lower the headpiece until it firmly touches the crown of the head.

Make sure the measurer’s eyes are at the same level as the headpiece.

Measure Weight

1. Use a digital scale. Avoid using bathroom scales that are spring-loaded. Place the scale on firm flooring (such as tile or wood) rather than carpet.
2. Have the child or teen remove shoes and heavy clothing, such as sweaters.
3. Have the child or teen stand with both feet in the center of the scale.
4. Record the weight to the nearest decimal fraction (for example, 55.5 pounds or 25.1 kilograms).

Measuring Arm Length

Measure Arm Length

The subject stands with the arms hanging loosely by the side of the body, fingers outstretched. A measurement is made from the acromiale (lateral edge of the acromion process, e.g., bony tip of shoulder) to the tip of the little finger. Measurement is made on the right side, following the anthropometric standard, though a measurement of either side would be assumed to be the same in most cases.

Skinfold Measurement Test

The skinfold measurement test is one common method of determining a person’s body composition and body fat percentage.

This test estimates the percentage of body fat by measuring skinfold thickness at specific locations on the body. The thickness of these folds is a measure of the fat under the skin, also called subcutaneous adipose tissue. Skinfold thickness results rely on formulas that convert these numbers into an estimate of a person’s percentage of body fat according to a person’s age and gender.

Procedures of fixing marks:

1. The adult or child should stand up straight and sideways to you. His/her arms should be relaxed, and legs should be slightly apart. His right elbow should be bent at 90^o angle with palm facing upward. Place the measuring tape with its zero mark just under the acromion process and extend the tape to the pointed part of the mid-pointed mark and mark it.

Tricep Skinfold

• Vertical fold
• Located on the posterior midline of the upper arm
• Measure halfway between the acromion (bony point of the shoulder) and olecranon processes (bony point of the elbow)
• Arm held freely to the side of the body

Biceps Skinfold

• Vertical fold
• Located on the anterior midline of the upper arm over the belly of the biceps muscle
• Located 1 cm higher than the level used to mark the triceps site

Subscapula Skinfold

• Diagonal fold
• Located 1 to 2 cm below the inferior angle of the scapula (the bottom of the shoulder blade)
• If you struggle to locate the bottom of the shoulder blade, then ask your client to raise their arm up behind their back – this should make the scapula become more prominent.

Suprailiac Skinfold

• Diagonal fold
• Located 1 cm above the anterior superior iliac crest (top of the hip bone)
• Locating this landmark may require you to ‘poke’ firmly through thick subcutaneous layers of fat to find the bone underneath.