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Getting a Grip on Body Composition
By Len Kravitz, Ph.D. and Vivian H. Heyward, Ph.D.

Health practitioners universally agree that too much body fat is a serious health risk. Problems such as hypertension, elevated blood lipids (fats and cholesterol), diabetes mellitus, cardiovascular disease, respiratory dysfunction, gall bladder disease, and some joint diseases are all related to obesity. Also, some research suggests that excessive accumulation of fat at specific body sites may be an important health risk factor (Wilmore, Buskirk, DiGirolamo, & Lohman, 1986). For instance, it appears that extra fat around the abdomen and waist is associated with higher risk of diabetes, heart disease, and hyperlipidemia. Individuals who accumulate a lot of fat around the waist (apple-shaped) are worse off than those who tend to accumulate fat in the thighs and buttocks (pear-shaped). The apple-shaped pattern of fat deposition is more commonly seen in men; whereas women tend to be pear-shaped.

Now, more than ever before, people are preoccupied with how much they weigh. New clients walk into our classes on a daily basis hoping that exercise will be the panacea. In an effort to lose weight and excess fat, Americans spent in 1989 an excess of 30 billion dollars for 54 million diet books and for services and products at 1500 weight control clinics (McArdle, Katch, & Katch, 1991). Yet, efforts such as these to achieve thinness are often based on popular misconceptions about body weight and body composition. Being thin does not necessarily reduce one's health risk. In fact, obsession with becoming thin often leads to serious eating disorders such as anorexia and bulimia. Thinness simply refers to weighing less than the recommended values in age-height-weight tables. Leanness, on the other hand, refers to the muscle, bone, and fat composition of your body weight. Although some lean individuals may actually weigh more than their "tabled" ideal body weight, low body fat lessens the risk of health problems.

Understanding and being able to explain the difference between healthy leanness and undesirable thinness is one important concept the fitness instructor, personal trainer, and exercise leader must share with clients. In addition, there are some other reasons to become more informed about body composition:
o To develop complete physical fitness profiles for clients.
o To monitor body fat loss and muscle growth resulting from exercise.
o To provide baseline data for nutritional counseling and treatment of obesity.
o To describe changes due to growth, development, maturation, and aging.
o To maximize the performance of athletes.

Body Composition
The body is composed of water, protein, minerals, and fat. A two-component model of body composition divides the body into a fat component and fat-free component. Body fat is the most variable constituent of the body. The total amount of body fat consists of essential fat and storage fat. Fat in the marrow of bones, in the heart, lungs, liver, spleen, kidneys, intestines, muscles, and lipid-rich tissues throughout the central nervous system is called essential fat, whereas fat that accumulates in adipose tissue is called storage fat. Essential fat is necessary for normal bodily functioning. The essential fat of women is higher than that of men because it includes sex-characteristic fat related to child-bearing. Storage fat is located around internal organs (internal storage fat) and directly beneath the skin (subcutaneous storage fat). It provides bodily protection and serves as an insulator to conserve body heat. The relationship between subcutaneous fat and internal fat may not be the same for all individuals and may fluctuate during the life cycle.
Lean body mass represents the weight of your muscles, bones, ligaments, tendons, and internal organs. Lean body mass differs from fat-free mass. Since there is some essential fat in the marrow of your bones and internal organs, the lean body mass includes a small percentage of essential fat. However, with the two-component model of body composition, these sources of essential fat are estimated and subtracted from total body weight to obtain the fat-free mass. Practical methods of assessing body composition such as skinfolds, bioelectrical impedance analysis (BIA), and hydrostatic weighing are based on the two-component (fat and fat-free mass) model of body composition.

Standards of Body Fatnessary
Our bodies require essential fat because it serves as an important metabolic fuel for energy production and other normal bodily functions. Referring to Table 1, you can see that the essential fat requirements are < 5% for men and < 8% for women. Normal body functions may be disrupted if body fat falls below the minimum level recommended for men (5%) and women (15%). The body fat ranges for optimal health (18%-30% for women and 10%-25% for men) are based on several epidemiological studies of the general population. Body fat percentages for optimal fitness and for athletes tend to be lower than optimal health values because excess fat may hinder physical performance and activity.

When prescribing ideal body fat for a client, you should use a range of values rather than a single value to account for individual differences. After age 20, you should expect at least 1-3% fat gain per decade up to the age of 60; thereafter fatness declines gradually. In addition, there is approximately a 2% loss of bone mass per decade in older populations. As a result of these changes, men and women who weigh the same at age 60 as they did at age 20 may actually have double the amount of body fat unless they have been physically active throughout their life (Wilmore et al., 1986).

Table 1. Standards of Fatness for Women and Men in Percent Body Fata
Women Men
(%) (%)
Essential fat < 8 < 5
Minimal fat weight 15 5
Most athletes 12-22 5-13
Optimal health 18-30 10-25
Optimal fitness 16-25 12-18
Obesity > 30 > 25
a (Wilmore, J. H., Buskirk, E. R., DiGirolamo, M., & Lohman, T. G. (1986). Body Composition:
A round table. The Physician and Sportsmedicine, 14(3), 144-162.

Assessing Body Composition
The search for valid methods of measuring body composition that are practical and inexpensive is an ongoing process for exercise scientists and nutritionists. Standard age-height-weight tables derived from life insurance data often incorrectly indicate individuals to be overweight. Some practical methods of measuring body composition include skinfolds, circumference (girth) measures, hydrostatic weighing, bioelectrical impedance, and near-infrared interactance. Other advanced methods discussed in research journals include isotope dilution, neutron activation analysis, magnetic resonance imaging, and dual-energy x-ray absorptiometry. Most practical methods have a 3% to 4% error factor in their prediction of body fat (Brodie, 1988). That is, if you were measured at 20% body fat you could be as low as 17% or as high as 23%. This error factor may be increased dramatically due to the skill (or lack of it) of the technician taking the measurements. The following sections will focus on three body fat measurement techniques that are often accessible to fitness professionals: hydrostatic weighing, bioelectrical impedance, and skinfolds.

Hydrostatic Weighing
Hydrostatic weighing is a valid, reliable and widely used technique for assessing body composition. It has been labeled the "Gold Standard" or criterion measure of body composition analysis. It is based on Archimedes' principle. This principle states that an object immersed in a fluid loses an amount of weight equivalent to the weight of the fluid which is displaced by the object's volume. This principle is applied to estimate the body volume and body density of individuals. Since fat has a lower density than muscle or bone, fatter individuals will have a lower total body density than leaner individuals.

As the person is being submerged, the air in the lungs must be exhaled completely. The air remaining in the small pockets of the lungs following a maximal expiration is referred to as the residual lung volume. The residual lung volume may be determined using a number of laboratory techniques or it is often estimated using age, height, and gender-specific equations. Once your body weight, the underwater weight, and the residual lung volume are known, total body density may be calculated. From the total body density, the percent body fat can be estimated using the appropriate age-gender equation. One limitation of hydrostatic weighing is that it is based on the two- component model (fat and fat-free mass) which assumes when calculating total body density that the relative amounts and densities of bone, muscle, and water comprising the fat-free mass are essentially the same for all individuals, regardless of age, gender, race or fitness level. It is now known that this is not the case. For instance, the fat-free body density of young Black men is greater than that of white men. Because of this, the lean body mass is overestimated and the body fat is underestimated for many Blacks. This explains the misleading information often seen in the media stating that some Black athletes have 1% or 2% body fat, which is actually incompatible with life. Also, after age 45 to 50, substantial changes in bone density, especially in women, invalidate the use of an assumed constant value for fat-free body density when converting total body density to percentage of body fat. This is why age and gender specific equations need to be used for estimating body fat. As researchers learn more about age-related changes in bone mineral, hydrostatic weighing will eventually provide a more accurate prediction of body fat for older men and women.

Bioelectrical Impedance Analysis
Your total body water constitutes the largest component (72%) of your fat-free body weight. Bioelectrical impedance analysis (BIA) is based on the fact that the body contains intracellular and extracellular fluids capable of electrical conduction. A non-detectable, safe, low-level current flows through these intracellular and extracellular fluids. Since your fat-free body weight contains much of your body's water and electrolytes, it is a better conductor of the electrical current than the fat, which contains very little water. So this technique is essentially an index of total body water, from which fat-free mass is estimated.

The popularity of the BIA method has grown significantly over the last few years because it is painless, quick, and easy to administer the test. To take the test, you lie on a testing table or floor and electrodes are attached to your hands and feet. You do not feel a thing as the current passes through your body. Average time for administering this test is about 10 minutes. The following BIA testing guidelines are important in order to keep the prediction error of the BIA method at no more than 4% (Heyward, 1991).
1. No eating or drinking within 4 hours of the test
2. No exercise within 12 hours of the test
3. Urinate within 30 minutes of the test
4. No alcohol consumption within 48 hours of the test
5. No diuretics within 7 days of the test
One drawback of using the BIA method is that the equipment is relatively expensive ($3,500 compared to skinfold calipers at $200). Also, it appears that the BIA method is more accurate for estimating body fat of persons within the optimal health category (18-30% women; 10-25% men). There is a tendency for BIA to overestimate percent body fat in very lean clients and underestimate body fat in obese clients. All in all, if the guidelines for testing are followed, the BIA method is a satisfactory method for assessing body composition of most people.

Skinfold Method
The skinfold method of measuring body fat is a practical, economical, and administratively feasible field technique for body composition analysis. It involves measuring the skinfold (subcutaneous fat) thickness at specific sites of the body. Most equations use the sum of at least three skinfolds to estimate body density from which body fat may be calculated. Skinfold measurement does not require expensive equipment and it can be routinely incorporated into many health promotion settings. Skinfold technicians can be trained rather easily, but must practice on at least 50-100 clients before the skinfold technique is mastered.

When using the skinfold method, it is assumed that the distribution of subcutaneous fat and internal fat is similar for all individuals. This assumption is not fully supported. It is now known that older subjects of the same body density and gender have proportionately less subcutaneous fat than their younger counterparts. There is considerable biological variation in the distribution of subcutaneous, intermuscular, intramuscular, and internal organ fat due to age, gender, and degree of fatness (Heyward, 1991). However, generalized skinfold equations have been developed to estimate the body fat of men and women varying greatly in age (18 to 61 yrs) and degree of body fatness (4 to 44% fat).

Accuracy of Skinfold Measurements
The accuracy of the skinfold method is dependent on the technician's skill as well as the type of caliper and the skinfold prediction equation used. When choosing a skinfold caliper for a health/fitness setting, the cost, durability, and degree of precision of the caliper are important considerations. Reasonably priced plastic calipers have a less precise measuring scale, and often provide variable pressure and a smaller range of measurement. Despite this, a number of researchers have reported only small differences between skinfolds measured with high quality calipers and plastic calipers for highly skilled technicians (refer to Guide to Skinfold Caliper for more information on where to purchase calipers). However, plastic calipers are not recommended for use by untrained technicians.

To assure accuracy, the skinfold technician must follow standardized testing procedures:
1. Take all skinfold measurements on the right side of the body.
2. Carefully identify and mark the skinfold sites.
3. Place the thumb and index finger approximately 3 inches (8 cm) perpendicular to the skinfold, following the natural cleavage lines of the skin.
4. Grasp the skinfold firmly with the thumb and index finger just slightly less than 1/2 inch (1 cm) above the marked site to be measured.
5. Do not release the skinfold during the measurement.
6. Place the jaws of the caliper approximately 1/2 inch (1 cm) below the thumb and index finger. Always release the caliper jaw pressure slowly.
7. The skinfold measurement should be taken 4 seconds after the pressure is released. Measure the skinfold to the nearest 1/2 to 1 mm.

You should take a minimum of two measurements at each site. It is advisable to take measurements in a rotational order rather than consecutive readings at the same site. If your values differ by more than 1 mm, take additional measurements. The client's skin should be dry and free of any oils and lotions. Skinfold measurements should not be done immediately after exercise due to the shift of body fluid to the skin. Fortunately, the time of day or the phase of the menstrual cycle will have little effect on the skinfold measurements.

As with many skills, the more you practice the better you will become at measuring skinfolds. It always helps if you have another trained technician to compare your results. For severely obese clients (> 45% body fat) you will not be able to measure their skinfold thickness accurately. One alternative for obese clients would be to use fat-specific equations (Segal et al., 1985) developed for the BIA method.

Measuring Sites for Women
Triceps: Take a vertical fold on the posterior midline of the upper arm halfway between the top of the shoulder and the elbow joint. Keep the elbow extended and relaxed.
Thigh: Take a vertical fold on the front aspect of the thigh, midway between the top of the knee cap and the hip.
Suprailium: Take a diagonal fold above the crest of the ilium (hip- bone), at the spot where an imaginary line comes down from the anterior line of the armpit (anterior axillary line).

Measuring Sites for Men
Chest: Take a diagonal fold half the distance between the anterior axillary line (line of armpit) and nipple.
Abdomen: Take a vertical fold at a lateral distance approximately 2 cm (3/4 inch) to the right of the umbilicus (belly button).
Thigh: Take a vertical fold on the front aspect of the thigh, midway between the top of the knee cap and the hip.

Target Body Fat
Keep a record of each client's estimated body fat. This is very useful information for you to track the success of the exercise program you have prescribed. It will also give you insight about changes you feel may be necessary. Knowing a person's body fat will help you determine a more realistic target body fat and body weight for them. For instance, let's assume you have a 30-year-old female client who weighs 135 lb and is 28% body fat. The actual fat weight for this person is 135 X .28 = 38 lb. Her lean body weight is 72% or 135 X .72 = 97 lb. If you set the initial body fat goal at 24% (which is 76% lean body weight), you can calculate her ideal body weight by simply dividing her current lean body weight (97 lb) by the prescribed lean body percentage (76%); 97 ÷ .76 = 128 lb. Therefore, to reach this new body fat level she needs to lose 7 lb of body fat. The following table summarizes the steps for calculating target body fat and target body weight.

Target Body Fat Calculation

1. Client's weight in lb 135 lb
2. Body fat measurement 28%
3. Fat weight (135 lb X 28%) 38 lb
4. Lean body weight (135 X 72%) 97 lb
5. Desired body fat % & lean body % 24% fat & 76% lean body weight
6. Desired weight (97 lb ÷ .76) 128 lb
7. Fat lb to lose 7 lb

This information is particularly valuable if a client is going on a weight loss diet. Oftentimes diets will result in loss of mostly lean body tissue and water. By tracking a client's body fat you can closely monitor what body composition changes are actually happening. Just knowing how many pounds a person has lost is insufficient. The goal of any weight control program is going to involve adjusting a person's exercise and dietary habits to reach that ideal percentage of body fat.

Body composition is an integral component of total health and physical fitness. As health/fitness practitioners, we need to educate the general population about the desirable degree of fatness and how to obtain it. By lessening obesity in our society, we will also have a positive impact in reducing the risk of a number of diseases including coronary heart disease, diabetes, hypertension and musculo-skeletal problems. Body composition evaluation should be included as a fundamental aspect of all physical fitness appraisals. It's time we started promoting leanness, not thinness, to enhance lifetime physical and mental well-being for our clients.

Brodie, D. A. (1988). Techniques of measurement of body composition Part II. Sports Medicine, 5, 74-98.
Heyward, V. H. (1991). Advanced fitness assessment & exercise prescription. Champaign: Human Kinetics Publishers.
Jackson, A.S. & Pollock, M.L. (1985) Practical assessment of body composition. The Physician and Sportsmedicine, 13, 5, 76-90
McArdle, W. D., Katch, F. I., & Katch, V. L. (1991). Exercise physiology: Energy, nutrition, and human performance (3rd ed). Philadelphia: Lea & Febiger.
Segal, K.R., Gutin, B., Presta, E., Wang, J. & Van Itallie, T.B. (1985) Estimation of human body composition by electrical impedance methods: A comparative study. Journal of Applied Physiology, 58, 1565-1571.
Wilmore, J. H., Buskirk, E. R., DiGirolamo, M., & Lohman, T. G. (1986). Body composition: A round table. The Physician and Sportsmedicine, 14(3), 144-162.
Guide to Skinfold Calipers
Adipometer Ross Laboratories
625 Cleveland Ave.
Columbus, OH 43216

Holtain Pfister Import-Export Inc.
450 Barel Ave.
Carlstadt, NJ 07072

Lange Cambridge Scientific Industries
527 Poplar St.
Cambridge, MD 21613

Slim-guide Creative Health Products
9135 General Court
Plymouth, MI 48170

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