Body Composition -- Chapter 4

1. Introduction
2. Essential and storage fat
3. Techniques of assessing body composition
4. Waist-to-hip ratio
5. Body Mass Index
6. Determining Recommended Body Weight
7. Conclusion

1. Introduction

Body Composition- a reference to the fat and non-fat components of the human body

• Height/Weight charts were used in the past -- They are INACCURATE (They do not identify critical fat values I the body)
• Healthy weight- The Body Weight at which there seems to be no harm to human health
• Obesity- Related to an excessive amount of body FAT

2. Essential and storage fat

• Essential fat- Needed for normal bodily functions (constitutes 3% of tot. fat in me, 12% in women
• Storage fat- Fat stored in adipose tissue, mostly beneath the skin (subcutaneous fat) and around major organs

  Fat serves 3 basic functions:

  • As an insulator to retain body heat
  • As an energy substrate for metabolism
  • As padding against physical trauma to the body

• Women and Men store fat in different places!

3. Techniques for assessing body composition

Body composition can be determined several different ways (use the same test for the pre-test and the post-test).

• Dual Energy X-Ray Absorptiometry (DEXA) 
  • A radiographic technique that uses very low-dose beams of X-ray energy to measure total body fat mass, fat distribution pattern, and bone density.
  • DEXA is not readily available to most fitness participants.
    
• Hydrostatic (underwater) weighing
  • The most accurate test available if done properly
  • Not feasible when testing large numbers
  • Major concern is the individuals ability to follow test procedures: Person must:
    • Force out all air from lungs
    • Completely submerge for 5 to 10 seconds
    • Remain calm while submerged
    • Repeat procedure 8 to 10 times

• Other tests are simpler, less expensive, and fairly accurate!

• Air Displacement
  • An individual sits inside a chamber (called a Bod Pod) where pressure sensors determine the amount of air displaced by the person.
  • The air volume with the person inside the chamber is subtracted from the air volume of the empty chamber.
    
• Skinfold thickness

• Based on the fact that approximately 1/2 body fat is subcutaneous- directly beneath the skin
• The test is done using pressure calipers
• Several sites must be measured
• Women: Triceps, Supraillium, Thigh
• Men: Chest, Abdomen, Thigh
• Measurements are taken on right side of the body

• Bioelectrical Impedance (requires costly equipment)

• A weak electrical current is run through the body at different points
• Lean tissue conducts electricity better than fat tissue

• Girth Measurements

• Measuring circumferences at various body sites (may not be accurate for athletic individuals or the very thin or obese).
• Sites- Women: Upper Arm, Hip, Wrist Men: Waist, Wrist

4. Waist-to-hip ratio

Evidence suggests that the way people store fat affects the risk of disease

• Some people store fat in the abdominal area (others around the hips and thighs)
• Obese individuals with a lot of abdominal fat are at a higher risk of chronic disease than those with fat around the hips and thighs
• A waist to hip measurement can determine which category one falls into (most men store fat at the waist, women at the hips and thighs).

5. Body Mass Index (BMI)

BMI uses height and weight to estimate fat values --- BMI = (Weight * 705 / height / height)

• The lowest risk from chronic disease is in the 22 - 25 range (overweight 25 - 30)
• Fails to differentiate between fat and non-fat

6. Determining Recommended Body Weight

• People who have too little body fat may be unhealthy
• To compute your own recommended body weight:

1. Determine your amount of fat weight (Weight * percent fat)
2. Determine your lean body mass (Total weight - fat weight) [LBM]
3. Select a desired body fat percentage (DFP)
4. Compute Recommended Body Weight --- RBW = LBM / (1.0 - DFP)

[LBM = Lean Body Mass | DFP = Desired Fat Percent | RBW = Recommended Body Weight]

7. Conclusion

• Skinfold thickness is probably the most practical way to estimate body fat
• When dieting, body composition should be assessed periodically
• The average person gains 1 pound per year starting at age 25

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