19- Body Comp

Question 1

What components of the body does body cell mass, fat free mass, and fat mass include?

Answer 1

Body cell mass: organs and skeletal muscle
Fat free mass: Organs, skeletal muscle, bone mass, extracellular fluid
Fat mass: Visceral, subcutaneous, and functional fat

Question 2

3 main phases of body composition change

Answer 2

1. Growth and development
2. Maturity
3. Aging

Question 3

What are some body composition trends during growth and development?

Answer 3

• No sex difference until ~5 years
• Body fat starts at around 14-16%, increases at 1 year old, decreases again in early childhood, followed by rebound adiposity and continual gain

Question 4

Body composition trends during maturity and aging

Answer 4

• Continual fat mass gain that varies depending on sex and race
• Declines with aging - mostly by skeletal muscle
• Changes in ffm mostly associated with bcm
• Amount of ffm that is bcm decreases with age (from 59% between 20-29 years to 46% between 80-90 years)
• Loss of muscle fibres may begin with loss or impairment of motor neurons
• Absolute reduction in type II muscle fibre; relative preservation of type I

Question 5

When does BMD peak?

Answer 5

20-30 years

Question 6

Most variable components of body comp

Answer 6

• Fat mass (most)
• Skeletal muscle mass (second most; accelerated decline after 65 years)
• Decrease in synthesis rate of myosin heavy chain
• Decreased stimulation of muscle PRO synthesis by AA (more AA needed)

Question 7

When does skeletal muscle decrease and what happens?

Answer 7

• Starts at mid-40s
• Associated with strength reductions and decreased muscle O2 uptake

Question 8

Skeletal muscle changes during aging and what happens?

Answer 8

• Decline starts in mid 40s
• Assoc with reductions in muscle O2 uptake and strength
• Thought to begin with impaired motor neurons
• Reduced synthesis of myosin heavy chains
• Decreased muscle synthesis with AA; more AA required
• Absolute reduction in type II fibres; relative preservation of type I fibres
• Lower maximal force and reduced shortening velocity
• Reduction in GH, IGF, androgens, estrogen/progesterone, and prevalence of insulin resistance

Question 9

Type I vs Type II muscle fibres

Answer 9

• Type I : Slow twitch; muscles assoc with posture and endurance; Red with lots of mitochondria; dependent on cell resp
• Type 2 : fast twitch; white; few mitochondria; uses glycolysis; dominant in muscles for rapid movement; prone to fatigue

Question 10

Sarcopenia

Answer 10

Age related loss of strength and muscle mass (disproportionate loss of strength - 2-4% compared to muscle mass - 0.8%)
- Defined by appendicular skeletal muscle 2SD below mean for young healthy adults