Week 4 - Muscle Ageing

Question 1

Define sarcopenia.

Answer 1

age related loss of muscle mass

Question 2

In reference to sarcopenia, answer the following.
- When does muscle mass begin to decline?
- What age does the slow phase of age-related muscle decline range from?
- By age 80, what % of total muscle mass can be lost?

Answer 2

• 25
• 25-50 years
• 50%

Question 3

Is strength loss greater in lower or upper body with ageing?

Answer 3

Lower body - 40% decline
Upper body - 33% decline

Question 4

Relationship between muscle power and ageing.

Answer 4

Muscle power decreases with age

Question 5

What underlies the functional declines (loss in muscle strength) with age?

Answer 5

1) A loss of muscle mass (fiber loss and atrophy)
2) Muscle quality is reduced
3) Neuromuscular alterations

Question 6

What is the average rate of muscle mass loss after 40 years old? What about after 70 years old?

Answer 6

• 8% per decade to 70 years old
• 15% per decade

Question 7

Is there a greater muscle mass loss relative to body mass in men or women?

Answer 7

Men

Question 8

What muscle fiber atrophies faster with age, type I or type II?

Answer 8

type II

Question 9

What is greater, losses in muscle strength or losses in muscle mass?

Answer 9

losses in muscle strength are far greater than muscle mass loss

Question 10

How is muscle quality reduced with age?

Answer 10

Increase in subcutaneous and intermuscular fat, and less muscle.
Increased non-contractile material.

Question 11

How does neuromuscular alterations explain loss in muscle strength as we age?

Answer 11

Aging results in motor unit loss which results in muscle fibers (predominantly type II) becoming denervated which causes muscle fiber atrophy or fiber loss.

Question 12

Denervation and reinnervation of muscle fibers

Answer 12

• Loss of motor neurons leaves fibers denervated.
  This results:
• Type II fiber loss
• Type II fiber atrophy due to less innervation (lower motor unit firing frequency)
• OR reinnervation of fibers by type I motor units.
• When fibers are reinnervated by other motor units this creates larger motor units that are less efficient.
• Denervation without reinnervation results in type II fiber loss.

Question 13

What are the two options for denervated muscle fibers when we have the loss of motor units?

Answer 13

1) Atrophy and loss
2) Atrophy and reinnervation

Question 14

How does denervation and collateral re-innervation alter muscle characteristics?

Answer 14

• Increased co-expression of myosin isoforms
• Decreased force output
• Decreased velocity of contraction and hence power
• Altered fatigue resistance

Question 15

The effect of reinnervation of fibers

Answer 15

• Increased size of motor units (make them less efficient)
• Preserves some muscle mass

Question 16

Why may fatigue resistance increase in old age?

Answer 16

Type II fibers innervated by type I motor units with age and so they behave more like type I fibers with a higher fatigue resistance. However, they produce less force.

Question 17

What is disease-related muscle wasting termed?

Answer 17

cachexia