Week 4 - Muscle Ageing Flashcards
Define sarcopenia.
age related loss of muscle mass
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?
- 25
- 25-50 years
- 50%
Is strength loss greater in lower or upper body with ageing?
Lower body - 40% decline
Upper body - 33% decline
Relationship between muscle power and ageing.
Muscle power decreases with age
What underlies the functional declines (loss in muscle strength) with age?
1) A loss of muscle mass (fiber loss and atrophy)
2) Muscle quality is reduced
3) Neuromuscular alterations
What is the average rate of muscle mass loss after 40 years old? What about after 70 years old?
- 8% per decade to 70 years old
- 15% per decade
Is there a greater muscle mass loss relative to body mass in men or women?
Men
What muscle fiber atrophies faster with age, type I or type II?
type II
What is greater, losses in muscle strength or losses in muscle mass?
losses in muscle strength are far greater than muscle mass loss
How is muscle quality reduced with age?
Increase in subcutaneous and intermuscular fat, and less muscle.
Increased non-contractile material.
How does neuromuscular alterations explain loss in muscle strength as we age?
Aging results in motor unit loss which results in muscle fibers (predominantly type II) becoming denervated which causes muscle fiber atrophy or fiber loss.
Denervation and reinnervation of muscle fibers
- 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.
What are the two options for denervated muscle fibers when we have the loss of motor units?
1) Atrophy and loss
2) Atrophy and reinnervation
How does denervation and collateral re-innervation alter muscle characteristics?
- Increased co-expression of myosin isoforms
- Decreased force output
- Decreased velocity of contraction and hence power
- Altered fatigue resistance
The effect of reinnervation of fibers
- Increased size of motor units (make them less efficient)
- Preserves some muscle mass