Lecture 15 - Body Composition Flashcards
what is body composition
body’s chemical and molecular composition
what are the different body composition models
- 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)
can we measure body fat
No, can only estimate
why do we measure body comp
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
what are the different ways we measure body comp
- densitometry/hydrostatic weighing
- DEXA
- air plethysmography
- skinfold
- bioelectric impedance
what is densitometry
densitometry measures body density
- hydrostatic (underwater) weighing
- muscle is heavier than water, fat lighter than water
- gold standard until DEXA developed
limitations of hydrostatic weighing
- lung air volume confounding
- conversion of body density to percent fat
- fat free density varies among ppl
Dexa
dual-energy X-ray absorptiometry
- quantifies bone and soft tissue composition
- precise and reliable but expensive and technical
air plethysmography (bod pod)
- another densitometry technique
- air displacement instead of water
- easy for subject, difficult for operator, expensive
- can’t have hair
skinfold technique
- most widely used field technique
- measures thickness at a minimum of three sites
- uses quadratic equations, reasonably accurate
bioelectric impedence
- 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)
fat free mass
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)
relative body fat (percent body fat)
- 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
essential fat for men vs women (cant function if its lower)
Male is 3% and women is 12%. Breasts are fat
why can’t we have a ideal body size/weight standard for elite athletes
- 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)
why is it inappropriate to use weight standards in sport
- 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
why is making weight bad for sport
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
severe weight loss by dehydration
- 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
how can extreme WL lead to chronic fatigue
under weight - >fatigue - > decreased performance and injury
- mimics overtraining and chronic fatigue syndrome
- underweight leads to substrate depletion
how can severe WL lead to eating disorders
- weight standards can lead to disordered eating
- anorexia nervosa, bulimia nervosa
- more prevalent with women in lean sports
how can severe WL lead to menstrual dysfunction
- 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
how can WL lead to bone mineral loss
- bone mineral loss is a serious consequence f athletic amenorrhea
- anorexia leads to a fracture rate 7x normal
female athlete triad
eating + menstrual + bone mineral disorders
- seen with women in lean-physique, low BW, or endurance sports
- skating dance, gymnastics, running or swimming
what must we consider when evaluating appropriate weight standards
- 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
what must we avoid when trying to achieve optimal weight
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)
