muscle ageing

Question 1

anatomy of skeletal muscle

Answer 1

thick filament- myosin
thin filament- actin
actin composition doesnt differ between type 1 and type 2 fibre
different in fibre types is myosin heavy chain isoform

1 motor neuron innovates 10s to 1000s of fibres, usually all same muscle fibre types

Question 2

estimates of muscle mass

Answer 2

• dual X ray absorptiometry (DXA) scan- lean tissue or fat free mass, appendicular lean
• bioelectrical impendence- fat free mass
• muscle cross sectional area/volume- MRI or CT scan
• muscle fibre type- muscle biopsy, stain and microscopy

Question 3

distribution of muscle mass

Answer 3

leg muscle mass is ~1/3 lower in older people
lower muscle mass in women
upper body muscle mass lower on average in both men and women

Question 4

muscle fibre type and number

Answer 4

study looking at muscle fibre area in vastus lateralis in men ages 70 and 77 (side of thigh)
- slow twitch maintained (T1)
- more t2x fibres lost with age
- more hybrid fibres with combination myosin heavy chain isoforms
- decline in fibre number seen in many studies

Question 5

motor units

Answer 5

some motor units lose appriox 25%
may lose a whole motor neuron
re innvervation by neighbouring units may produce fibre type groupding to make up for lost motor neuron

Question 6

mechanisms of muscle loss

Answer 6

• neural- denervation- apoptosis and reinnervation of fibres
  -endocrine- decreased testosterone, decreased GH = decreased muscle protein accretion + decreased IGF1= increased rate of muscle protein degradation
• cytokine- inflammation, increased IL-6 production, increased rate of muscle protein degradation
• metabolic- reduced mitochondrial density= reduced ATP production and muscle protein syntheis
• satellite cells- decreased mechanogrowth factor= decreased proliferative capacity of satellite cells, decreased satelite cell proliferation= reduced capcity for repair, decreased satellite cell number= decreased muscle fibre size

Question 7

testing muscle function

Answer 7

lab tests- isometric strenght- dynamometry
rate of force development/power- isokinetic dynamomotry, leg power rig, jumping mechanogrpahy
clinical tests- chair stand, grip strength

Question 8

grip strength and mortality

Answer 8

grip strength is strong predictor for different types of mortality
changes that contribute to muscle loss are also contributing to increased risk of disease and frailty

Question 9

change in power

Answer 9

study looking at 10 year changes in knee extensor power velocity relationship
greatest decline in power in older group
muscle power needed for a lot of daily activities and leads to a decline in general activity
2.2% loss in men
2.4% loss in women
greater loss in lower body and higher velocity

Question 10

causes of reduced strength

Answer 10

reduced muscle mass- specified torque also declines
reduced muscle quality
- greater intramuscular fat/connective tissue accumalation
- altered contractile properties- myosin glycation/oxidation
- altered metabolic properties- mitochondrial function
- changes in muscle architecture- pennation angle
- increased tendone compliance- suboptimal sarcomere length
- reduced activation

Question 11

functional threshold

Answer 11

minimal level of ability required to allow function
once threshold is crossed, there is limited function
can reverse loss of muscle mass by doing resistance training to increase the muscle mass by doing resistance training to increase the muscle mass, allowing individuals to get back to doing daily activities
reduced function=reduced activity=further limitiation (cycle)

Question 12

variability in muscle ageing

Answer 12

genetics
diet and nutrition
health/exercise throughout younger life