L11 Muscle Disuse and Atrophy

Question 1

How can the degree of muscle atrophy be measured?

Answer 1

Weight the muscle
Anthropometry - measurement of the limb. these ca have errors and are inaccurate
Skinfold measure - cheap, inaccurate
MRI, NMRI, MRT - scam of limb
CAT scan / CT scan - expensive
DEXA scan (less radiation than flying to the USA)

Question 2

Explain the ratio of muscle CSA to Mean Fibre CSA in relation to fibre number

Answer 2

If change in muscle CSA is proportional to change in mean fibre CSA then fibre number is unchanged.

Question 3

How does muscle waste happen?

Answer 3

Steady state protein turnover
Can be a decreases synthesis of protein or increases degradation
Protein (structural) turnover = 1.46% per day
Myofibrilar protein turnover takes 70 days
Sarcoplasmic fraction turnover = 25 days

Question 4

How much of motor neurone activity is being used for the injured limb following limb immobilisation?

Answer 4

5-15%

After limb fracture, pain is likely to cause similar reductions

Question 5

When immobilised after injury, what is likely to happen to some muscles to the tonic (low frequency action potentials for long time) motor neurone activity patterns?

Answer 5

They are likely to become more phasic (short and quick)

Question 6

which fibre is thought to be the ‘default state’ and which is the adapted state?

Answer 6

type IIb is the default state where as type I is the adapted state

Question 7

If we fix a muscle in a short or resting length then what will occur?

Answer 7

Atrophy due to losing sarcomeres

Question 8

If we fix a muscle in a lengthened position then what may occur?

Answer 8

Hypertrophy and possible differences between fibre types regarding whether increase in sixe is maintained - adding sarcomeres

Question 9

What happens to the connective tissue after immobilization in a shortened position. How can this be prevented?

Answer 9

Increase in collagen after immobilization. Muscle will be stiffer. This occurs because of loss of sarcomeres.
Both stimulation and stretch prevent collagen accumulation.

Question 10

What happens to enzyme activity with immobilization?

Answer 10

All enzyme activities decrease
Slow muscle - oxidative enzymes decrease more than glycolytic
Fast Muscle - glycolytic enzymes decrease more than oxidative

Question 11

After 3 weeks of immobilization what %age of muscle fibres decrease for each fibre type?

Answer 11

Type 1 = 13%
Type 2 = 10 %
Type x = 10%