9-10. Sarcopenia Flashcards
By what mechanism does muscle atrophy and weakness affect every person in their lifetime?
Aging
Define sarcopenia.
Age-associated loss of skeletal muscle mass and function
What % muscle loss defines sarcopenia? Age ranges?
Loss of 1-2% of lean mass per year after the age 50, w/ accelerated loss after age 65
The regulation of skeletal muscle involves a balance b/t what 2 processes?
Protein synthesis vs. Protein degredation
What are the sequential pathways that regulate muscle growth and atrophy throughout life?
- Myogenesis
- Postnatal growth
- Adult maintenance and adaptation
- Aging
What differentiates b/t adult maintenance and aging w/ regards to atrophy & hypertrophy?
- Adult maintenance and adaptation = change in fiber size, but not # of fibers
- Aging = change in both fiber size and number
What stressors contribute to muscle growth and atrophy?
- Load
- Neural activity
- Growth factors and hormones
- Inflammation, cytokines
- Metabolic stress
Why should peeps care about sarcopenia? What are the consequences of this disease?
Relationship b/t loss of muscle and:
- loss of independence
- nursing home admissions
- increased incidence of falls and fractures
- increased mortality
In general, what % loss of capacity limits normal functioning? Results in failure?
- 30% limits normal functioning
- 70% results in failure
What are the stages of muscle mass maintenance over a lifetime?
- Early life: Growth and development to maximize peak
- Adult life: maintaining peak
- Elderly life: minimizing loss
What does the frailty threshold on a functional capacity vs. age graph signify?
Reduced functional capacity and increased potential for injury
What causes the significant loss of muscle CSA seen in sarcopenia?
- loss of muscle fibers
- loss of fiber area
- increase in the amount of fat and connective tissue w/in the muscle
Do we see a greater decrease in type I or II muscle fibers loss as a result of sarcopenia?
Type II (fast) fibers
How does sarcopenia affect muscle strength?
Decrease
How does sarcopenia affect muscle twitch?
Smaller and slower contraction
What factors account for the slowing of muscle contraction time?
- Loss of sarcoplasmic volume and Ca2+ pumping capacity w/ aging
- Decrease in density of dihydropyridine receptors (DNPR)
How does sarcopenia affect muscle force and power?
Decrease
How does sarcopenia affect specific force?
No change
As peeps age, how does the relationship b/t muscle mass and force output change? Significance?
Relationship becomes weaker:
- muscle strength is lost faster than muscle mass
- gaining mass doesn’t prevent aging-related strength loss
How do motoneuron and motor units change w/ age?
- decrease in # of motoneurons
- Increase in size of motor units due to collateral sprouting
- delayed regeneration of injured motor axons w/ aging
What is the significance of motor units increasing in size w/ aging?
Decreased capacity for fine motor skills
What is collateral sprouting?
- Neurons become denervated
- Axons close to them have to sprout and innervate those fibers
- Motor units become larger
- Fibers group by type (slow vs. fast)
What is the rate limiting step of protein synthesis?
Initiation
How do the elderly show a “resistance to anabolism”?
As we age, the same level of loading results in less protein synthesis or muscle hypertrophy
