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Chapter 9

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Simon Fraser University
Biomedical Physio & Kines
BPK 143
Tony Leyland

BODY COMPOSITION Chemical composition of the human body by mass Body composition of a typical man and woman ( 20-24 years old) - Getting reliable body composition data is expensive - Most people do not know what their body composition should be - There is no ideal percent body fat for every individual - Pinching the subcutaneous fat (adipose tissue, below the skin) can give some useful information - Essential fat is essential for life, as it includes fat around nerves, in the brain, and around other essential organs - Non-essential fat is fat that acts as an energy store PERCENT BODY FAT - The most important consideration when looking at body composition - Percentage of lean tissue and bone density are also very important - Its difficult to measure percent body fat - Another problem with percent body fat estimates occurs when individuals do not exercise in an attempt to lose body fat - It may be successful, but often lose a considerable amount of muscle tissue as well - Percent of body fat may not go down and may even increase when overall body weight done down by losing both fat and muscle and possibly some bone density HEIGHT-FOR-WEIGHT TABLES - Used by insurance companies to predict the future health of potential policyholders - Its not a measure of body composition - Height-for-weigh tables show ranges of weights that are associated with the lowest mortality rates among policyholders - Show “desirable” weights rather than “average” weights - Convenient to use and work for large population - Problems with the height-for-weight tables are 1) Height-for-weight tables do not consider body composition, as they don’t distinguish between fat and other tissues, such as muscle and bone. Body weight doesn’t always reflect obesity, which is a measure of body fatness. Muscular athletes, for example, may have higher than “normal” weight and still have low percent body fat. 2) Most of the data in the Metropolitan height-for-weight tables comes from white, middle-class, American males. This is not a representative sample of the general North American population. The tables apply to people aged 25 to 59, and therefore don’t cover younger adults or the growing number of people over 60. 3) Many height-for-weight tables include frame size as a classification variable, but they do not specify what criteria to use to determine frame size. BODY MASS INDEX - - Mass in kilograms and height in metres - Not an assessment of body composition - Severs a function for epidemiologists and health officials who are tracking population trends in obesity - Useful because you can easily and cheaply get the BMIs of thousands of objects - BMI is an excellent tool for some applications, but not for all - BMI is not as useful for individual assessment as it is for assessing populations - Some people with high BMI simply because they have a large percentage of muscle and higher bone density, not higher fat levels - A very low BMI score can be associated with individuals who do a large volume of weight-bearing aerobic exercise or can be due to the result of poor eating habits and eating disorder - You can use the BMI in individual assessment, but only with additional information - Having a low BMI may not mean you are underweight, might be genetically very lean and have a small bone structure SKINFOLD MEASUREMENT - A special caliper used to measure the thickness of a double layer of skin and subcutaneous fat - Two ways to use skinfold measurement 1) Add the scores from the various measurement and use the value as an indication of the relative degree of fatness among subject 2) Use skinfold measurements in equations that predict percent body fat - There can be considerable error introduced into the estimation of percent body if the person isn’t experienced - Good thing about skinfold measurements is that they are real data collected directly from subjects - They provide a good estimate of the amount of subcutaneous fat in the region of the caliper measure - Subcutaneous fat is a deep-lying fat in the torso, which is closely associated with health problems WAIST GIRTH AND WAIST-TO-HIP RATIO - Females tend to have a large proportion of their fat in their breats and gluteal-femoral region (buttocks and thighs) - They are considered essential fat, as it is necessary for reproductive capacity - The most “risky” fat is non-essential visceral adipose tissue ( fat deposited deep in the abdomen) - Associated with type 2 diabetes, coronary heart disease, and hypertension - Waist-to-hip ratio and/or waist girth are good indicators of health risk - Health risks increase if the waist-to-hip ratio is above 0,9 and for women if it is above 0.8 - Health risks increase with waist circumferences above 40 inches for men and 35 inches for women - Waist-to-hip ratio and waist girth are body circumference measures and not body composition measures - Subject on the left would have high skinfolds in the torso compared with the subject on the right - Combination of measures is better than just individual measurement VOLUME DISPLACEMENT AND UNDERWATER WEIGHING - Estimate tissue densities by a water displacement or underwater weighing procedure - - There are differences in the densities and/or proportion of those tissues comprising the lean body mass - Males need about three to four percent body fat to live - Its accurate for an average individual, but the standard equations used to estimate percent body fat from whole body density are not appropriate for all segments of the population DEXA - Dual energy X-ray Absorptioometry - A technology that use an X-ray technique to look at the density of the body and can then estimate the amount of lean and fat tissue, as well as bone density - Less time-consuming and prone to a small percentage of error BIOELECTRICAL IMPEDANCE ANALYSIS AND OTHER TECHNIQUES - Bioelectrical impedance analysis (BIA) machines are used to measure the body’s electrical resistance - Detect changes in electrolyte levels and work on the principle that lean tissue has a far greater electrolyte content than fat - The less electrical resistance measured, the more lean tissue a person has and, by inference, the less fat - Percent body fat test by BIA is either overestimated or underestimated, due to variations in body water levels and electrolyte concentration WHAT OTHER MEHODS ARE THERE TO ASSESS BODY COMPOSITION? - The best scenario is to use a combination of assessment tools OVERWEIGHT (OVER-FAT) AND OBESITY AS A HEALTH PROBLEM - High intensity works help normalize hormonal levels better than only performing low power-output exercise - Correlation is not causation - Obesity is not the health problem, but that factors such as poor diets, inactive lifestyle, weight cycling, and possibly weight loss itself are the real culprits - If you are active, eat well, and maintain a relatively stable body weight, your body composition is not a critical factor in your physical health - People with relatively high levels of body fat who exercised regularly had fewer health risks than a similar group of individuals who were thin and did not exercise - Obesity and death resulting from heart disease and other major killers missed the important influence of exercise - Fitness and proper diet are the keys - Being fit doesn’t eliminate the risk of everything, but rather that you can stay overweight, and even obese, if you are fit and be just as healthy, in terms of mortality risk, as lean, fit people - Obese individuals who are fit develop diabetes at about the same rate as lean individual who are unfit - Genotype + environment = phenotype IS BODY COMPOSITION A COMPONENT OF FITNESS? - Component of fitness relate to a physiological function - Body composition is an anatomical snapshot of the body - To argue that percent body fat is a component of fitness is t
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