Lecture 15 - Body Composition

Question 1

what is body composition

Answer 1

body’s chemical and molecular composition

Question 2

what are the different body composition models

Answer 2

• chemical model (fat vs protein vs CHO vs H2O vs minerals)
• anatomical model (adipose tissue vs muscle vs organs vs bon vs other)
• two-compartment model (fat mass vs fat free mass)

Question 3

can we measure body fat

Answer 3

No, can only estimate

Question 4

why do we measure body comp

Answer 4

provides more information
- heigh and weight not enough to know fitness status
- incre body fat leads to decrease performance
- a bit more precise then BMI

Question 5

what are the different ways we measure body comp

Answer 5

• densitometry/hydrostatic weighing
• DEXA
• air plethysmography
• skinfold
• bioelectric impedance

Question 6

what is densitometry

Answer 6

densitometry measures body density
- hydrostatic (underwater) weighing
- muscle is heavier than water, fat lighter than water
- gold standard until DEXA developed

Question 7

limitations of hydrostatic weighing

Answer 7

• lung air volume confounding
• conversion of body density to percent fat
• fat free density varies among ppl

Question 8

Dexa

Answer 8

dual-energy X-ray absorptiometry
- quantifies bone and soft tissue composition
- precise and reliable but expensive and technical

Question 9

air plethysmography (bod pod)

Answer 9

• another densitometry technique
• air displacement instead of water
• easy for subject, difficult for operator, expensive
• can’t have hair

Question 10

skinfold technique

Answer 10

• most widely used field technique
• measures thickness at a minimum of three sites
• uses quadratic equations, reasonably accurate

Question 11

bioelectric impedence

Answer 11

• electrodes on ankle, foot ,wrist and hand
• current passes from proximal to distal sites
• fat free mass good conductor, fat poor conductor
• reasonably accurate, could be better (affected by menstrual cycle)

Question 12

fat free mass

Answer 12

includes muscle
- important variable for athletes to know
- greater FFM is good for power, strength and muscle endurance but bad for aerobic endurance (more mass to carry)

Question 13

relative body fat (percent body fat)

Answer 13

• fat: dead weight but useful energy store
• less fat usually better = better performance
• exceptions: sumo wrestlers, swimmer (more body fat make them float better and spend less time keeping themselves up), weight lifter

Question 14

essential fat for men vs women (cant function if its lower)

Answer 14

Male is 3% and women is 12%. Breasts are fat

Question 15

why can’t we have a ideal body size/weight standard for elite athletes

Answer 15

• elite athletes define optimal performance; they are the standard
• they define performance by not necessarily optimal body (someones body comp might not exactly make sense for the sport but they surprisingly perform very well)

Question 16

why is it inappropriate to use weight standards in sport

Answer 16

• its seriously abused by coaches and player, spend to much time to have a certain body type instead of performance
• misconception that small weight loss good, large weight loss better
• can lead to decrease performance, eating disorders

Question 17

why is making weight bad for sport

Answer 17

i.e. wrestling, boxing
- weight classes can force extreme weight loss
- trying to compete in class that is too low leads to injury and poor health

Question 18

severe weight loss by dehydration

Answer 18

• fasting, extreme caloric restriction leads to water loss (water mass loss)
• 2-4% weight loss as water leads to impaired performance
• risk of kidney, cardiovascular dysfunction, death

Question 19

how can extreme WL lead to chronic fatigue

Answer 19

under weight - >fatigue - > decreased performance and injury
- mimics overtraining and chronic fatigue syndrome
- underweight leads to substrate depletion

Question 20

how can severe WL lead to eating disorders

Answer 20

• weight standards can lead to disordered eating
• anorexia nervosa, bulimia nervosa
• more prevalent with women in lean sports

Question 21

how can severe WL lead to menstrual dysfunction

Answer 21

• delated menarch (first period), ogliomenorrhea, or amenorrhea (altered or irregular menstrual cycle)
• prevalent in low body weight sports
• due to caloric intake < caloric expenditure we don’t have enough energy to have a period

Question 22

how can WL lead to bone mineral loss

Answer 22

• bone mineral loss is a serious consequence f athletic amenorrhea
• anorexia leads to a fracture rate 7x normal

Question 23

female athlete triad

Answer 23

eating + menstrual + bone mineral disorders
- seen with women in lean-physique, low BW, or endurance sports
- skating dance, gymnastics, running or swimming

Question 24

what must we consider when evaluating appropriate weight standards

Answer 24

• an inapproriate standard risks athletes health
• body composition, not total body weight
• optimal range of percent body fat
• account for sex differences
  weight standards are not always appropriate
• technique measurement error
• not all athlete perform best at ideal composition

Question 25

what must we avoid when trying to achieve optimal weight

Answer 25

avoid fasting and crash diets
- causes more water and muscle loss, less fat loss
- ketosis accelerates water loss
Optimal WL: decrease in fat mass and increase FFM
- moderate caloric restriction + exercise
- calorix deficit ~200 to 500kcal/day (3500kcall = -1lb of fat)
- lose no more than 0.5 to one kg a week (consider anorexia)
- when near goal, slow weight loss further (slow WL)