1. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 28 Body Composition Assessment

2. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Determining Body Frame Size Body frame size is a way to evaluate “normalcy” of body weight with standardized charts Defined by a combination of stature and bony widths since it relates to fat-free body mass and not body fat Measurements: –Stature measured in cm –Biacromial diameter (cm): The distance between the most lateral projections of the acromial processes –Bitrochanteric diameter (cm): The distance between the most lateral projection of the greater trochanters

3. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Limitations of Height-Weight Tables Use unvalidated estimates of body frame size Developed from data derived primarily from white populations Specific focus on mortality data that may not reflect obesity-related comorbidities Provide no assessment of body composition

4. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Overweight, Overfat, and Obesity Overweight: A body weight that exceeds some average for stature, and perhaps age, usually by some standard deviation unit or percentage –Frequently accompanies an increase in body fat, but not always Overfatness: When body fat exceeds an age- and/or gender-appropriate average by a predetermined amount Obesity: The overfat condition that accompanies a constellation of comorbidities

5. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Body Mass Index Derived from body mass and stature Used to assess “normalcy” for body weight BMI = Body mass (kg) ÷ stature (m 2 ) As BMI increases, so does the risk for certain diseases No absolute BMI standard exists to classify children and adolescents as overweight and obese

6. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins BMI, weight classifications, and associated health risks

7. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins BMI Limitations Current classification for overweight assumes that the relationship between BMI and percentage body fat remains independent of age, gender, ethnicity, and race Fails to consider the body’s proportional composition or body fat distribution Factors other than excess body fat, such as bone, muscle mass, and increased plasma volume induced by exercise training affect the numerator of the BMI equation The possibility of misclassifying someone as overweight pertains particularly to some athletes

8. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Review Body mass index is derived from: a.Body mass and stature b.Body mass and girth measurements c.Skinfolds d.Stature and skinfolds

9. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer Body mass index is derived from: a.Body mass and stature b.Body mass and girth measurements c.Skinfolds d.Stature and skinfolds

10. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins The Human Body Composition Component model: –Three: Water, protein, fat –Four: Water, protein, bone mineral, fat Reference man and reference woman: –Divides body mass into lean body mass, muscle, and bone, with total body fat subdivided into storage and essential fat –Reference man is taller and heavier, the skeleton weighs more, and has a larger muscle mass and lower body fat content than the reference woman

11. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Essential and Storage Fat Essential fat: –Fat in heart, lungs, liver, spleen, kidneys, intestines, muscles, and lipid-rich tissues of the central nervous system and bone marrow –Normal physiologic functioning requires this fat Storage fat: –Fat primarily in adipose tissue 83% pure fat, 2% protein, and 15% water –Visceral fat

12. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Fat-Free Body Mass and Lean Body Mass Lean body mass: Non–sex-specific essential fat equivalent to approximately 3% of body mass Fat-free mass: Body mass devoid of all extractable fat Reference man: 12% storage fat and 3% essential fat Reference woman: 15% storage fat and 12% essential fat

13. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Reference man and woman

14. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Leanness, Regular Exercise, and Menstrual Irregularity Physically active women increase their likelihood for: –Delayed onset of menstruation –Oligomenorrhea –Amenorrhea Two possible hypotheses: –Exercise stress hypothesis: Prolonged physical stress may disrupt hypothalamic–pituitary–adrenal axis and modify output of gonadotropin-releasing hormone –Energy availability hypothesis: Fat reserves inadequate for pregnancy induce stop ovulation

15. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Common Techniques to Assess Body Composition Direct measurement by chemical analysis of the animal carcass or human cadaver –One technique dissolves the body in a chemical solution to determine its mixture of fat and fat-free components –Another physically dissects fat, fat-free adipose tissue, muscle, and bone

16. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Common Techniques to Assess Body Composition cont’d Indirect estimation: –Hydrostatic weighing using Archimedes’ principle –Skinfold thickness and girth measurements –X-ray and magnetic resonance imaging –Total body electrical conductivity or bioimpedance –Near-infrared interactance –Ultrasound –Computed tomography –Air plethysmography

17. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Computing Percentage Body Fat An equation that incorporates whole-body density estimates the body’s fat percentage Siri equation: –Percentage body fat = (495 ÷ body density) – 450 –Assumes: Two-component model of body composition Each of these densities remains relatively constant among individuals Densities of the lean tissue components of bone and muscle remained the same among individuals

18. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Limitations of Density Assumptions Density values for fat-free and fat tissue compartments represent averages for young and middle-aged adults, though they vary among individuals and groups –FFM density is higher for blacks and Hispanics –Racial differences also exist among adolescents –Overestimate FFM and underestimates percentage body fat in blacks and Hispanics Modification of the Siri equation computes percentage body fat from body density for blacks: –Percentage body fat=(437.4 ÷ body density) – 392.8

19. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Review The Siri equation assumes that the densities of the lean tissue components of bone and muscle remain the same among individuals. a.True b.False

20. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer The Siri equation assumes that the densities of the lean tissue components of bone and muscle remain the same among individuals. a.True b.False

21. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Computing Fat and Fat-Free Mass Fat mass = body mass × (% fat/100) Fat-free body mass = body mass × fat mass

22. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Skinfold Measurement Sites Triceps: Vertical fold at posterior midline of right upper arm, halfway between tip of shoulder and tip of elbow Subscapular: Oblique fold, below right scapula’s lower tip Iliac: Slightly oblique fold, just above the right hipbone (crest of ileum); the fold follows the natural diagonal line Abdominal: Vertical fold 1 inch to the right of umbilicus Thigh: Vertical fold at the midline of right thigh, 2/3 the distance from the middle of the patella to the hip Chest: Diagonal fold on the anterior axillary line Biceps: Vertical fold at right upper arm’s midline

23. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Anatomic skinfold locations

24. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Girth Measurements Right upper arm (biceps): Arm straight and extended in front of the body; measurement taken at midpoint between the shoulder and the elbow Right forearm: Maximum girth with arm extended in front of the body Abdomen: 1 inch above the umbilicus Buttocks: Maximum protrusion with heels together Right thigh: Upper thigh, just below the buttocks Right calf: Widest girth midway between ankle and knee

25. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Landmarks for girth measurements

26. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Bioelectrical Impedance Analysis Small alternating current flowing between two electrodes passes more rapidly through hydrated fat-free tissues and extracellular water than through fat or bone tissues because of lower electrical resistance of fat-free tissues Impedance to electric current flow is calculated: –R=V/I, where R=resistance, V=volume, I=current Represents a noninvasive, safe, relatively easy, and reliable means to assess total body water Requires standardized conditions: Electrode placement, body position, hydration status, plasma osmolality and sodium concentration, skin temperature, recent physical activity, and previous food and beverage intake

27. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Average Body Fat Young adult men: 12-15% Young adult women: 25-28% No systematic evaluation exists for body composition of the general population to warrant establishing norms or precise recommended values for body composition The general trend indicates a tendency for percentage body fat to steadily increase with advancing age

28. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Determining Goal Body Weight Goal body weight (kg) = fat-free body mass ÷ (1.00 – desired %fat)

29. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Review Which of the following is not an anatomic location commonly used to measure skinfolds? a.Triceps b.Subscapular c.Thigh d.Forearm

30. Copyright © 2010 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer Which of the following is not an anatomic location commonly used to measure skinfolds? a.Triceps b.Subscapular c.Thigh d.Forearm