L13 Muscle Fatigue: concepts and mechanisms

Question 1

Define fatigue in terms of muscle force generating capacity

Answer 1

= failure to maintain (or repeatedly generate) the required or expected force

Question 2

Define weakness

Answer 2

Failure to generate the required or expected force on first testing or attempted performance

Question 3

The size of the M-wave is what? and shows what?

Answer 3

= Muscle Mass action potential
It shows the activation of the muscle.
A larger M-wave means more of the muscle is activated.

Question 4

What is TMS?

Answer 4

Transcranial Magnetic Stimulation

- how to electronically stimulate the brain to cause a contraction

Question 5

What can synaptic failures be due to?

Answer 5

1. Disease
2. Blockage of neuromuscular junctions with a drug
3. Cooling a neuromuscular junction
4. Doing a too high electrical stimulation for too long in the lab

Question 6

Muscle fibre action potential failure due to:

Answer 6

1. V high stimulus frequency for 1-2 seconds in the lab
2. Slightly lower frequency for a little longer
3. Can be due to pumping capacity of K+ & an accumulation of it in the extra-cellular space

Question 7

What does a rapid recovery of force and m-wave when frequency of stimulation is reduced show?

Answer 7

That fatigue is neurological here rather than a problem with a muscle

Question 8

A muscle will generate more force for longer if firing rate is ____ in a prolonged maximal voluntary effort

Answer 8

reduced

Question 9

How does your body reduce neural drive to avoid high frequency firing ?

Answer 9

Feedback from the muscle signals the changing status of the muscle. This reduces the excitability of the motor neuron and higher centres –> Afferent feedback controls muscle recruitment

Question 10

Interpolating a twitch electrically into a movement will show if any fibres aren’t being recruited.

Answer 10

The larger the increase means more unused fibres