neuromuscular fatigue concepts

Question 1

where is the distinction between the CNS and PNS in terms of fatigue

Answer 1

peripheral = below motor end plate / NM junction

Question 2

what is the response to sustained MVC

Answer 2

all muscle fibres recruited at the start of the MVC
- high amplitude of the EMG at beginning and decays
- gradually muscle fibres get tired and rely more on type 1 muscle fibres

Question 3

what is the response to sustained sub max contraction

Answer 3

• slow fibres recruited first
• since type 1 will fatigue, more type 2 recuited to maintain force
• EMG amplitude increases as contraction continues because type 2 have higher amplitude on EMG

Question 4

what is the source of central fatigue

Answer 4

group III/IV afferents send signals back to the brain, brain is inhibited and reduce central motor drive

Question 5

what is the source of peripheral fatigue

Answer 5

from NMJ - anything that disrupts the activation of muscle is peripheral fatigue

Question 6

what is neuromuscular fatigue

Answer 6

reduction in maximal force output

Question 7

what is the process of ITT

Answer 7

stimulate the aMN of desired muscle
- stimulated on top of MVC to reach max activation
- stimulated after MVC to see the resting twitch

Question 8

what is the superimposed twitch

Answer 8

extra force created by electrical stimulus
shows how much of the fatigue is the brain deficit
measures central fatigue

Question 9

what can an increase in superimposed twitch mean

Answer 9

lower activation from brain on the whole MU

Question 10

what can a decrease in amplitude of resting twitch mean

Answer 10

deficit in muscle’s ability to produce force

Question 11

how is max voluntary activation measured

Answer 11

measured by having the participant perform an MVC
then stimulating the muscle on top of it to see the force produced when all muscle fibres produce force

Question 12

what are the 5 mechanisms of peripheral fatigue

Answer 12

• NM junction
• sarcolemma
• excitation contraction coupling
• metabolic alterations
• slowing of relaxation

Question 13

what is the role of NM junction in peripheral fatigue

Answer 13

• inhibition of presynaptic ending
• limited transmitter substance
• inability for post synaptic membrane to be excited

Question 14

what is the role of sarcolemma in peripheral fatigue

Answer 14

• changes in the electrical property of the muscle surface membrane
• changes in the intra/extracellular Na+ and K+

Question 15

what is the role of excitation contraction coupling in peripheral fatigue

Answer 15

• disruption in Ca2+ release or uptake

Question 16

what is the role of metabolic alterations in peripheral fatigue

Answer 16

• ATP availability at the myosin head chain
• metabolites accumulation
• PCr, glucose, and glycogen concentrations
• accumulation of H+ ion, Pi, and ammonia

Question 17

what is the role of slowing of relaxation in peripheral fatigue

Answer 17

• disruption in Ca2+ release or uptake

Question 18

what are some factors that may modulate central motor output

Answer 18

music, sleep, prior experience, time deception, knowledge of end point, presence of competitors, etc

Question 19

what is corollary discharge

Answer 19

internal copy of motor commands that is sent to the brain’s sensory system
- sensory can inhibit motor area if its too much sensory feedback
- allows the brain to predict the sensory consequences of the motor command
- helps distinguish between self generated sensations and external stimuli

Question 20

what is the relation between corollary discharge and RPE

Answer 20

higher corollary discharge = higher RPE
exercising larger muscle groups = more signals sent = higher RPE

Question 21

what is the sensory afferent feedback model

Answer 21

evidence for critical threshold of peripheral fatigue
- larger increase in peripheral fatigue (larger decrease in power output) in trial with no sensory feedback compared to when they could feel their legs
- shows that sensory feedback modulates muscle power output as signals to the CNS