central fatigue

Question 1

central fatigue

Answer 1

related to rediced neural output of central structures (brain)

Question 2

central governor model

Answer 2

predicts that neural control systems in the brian and spinal cord establish the number of motor units that are activated in the exercisig muscles, specifically to ensure that homeostasis is maintained

the brain continuously monitors physiological signals from the body, including factors like oxygen levels, muscle fatigue, and temperature.
based on this information, the brain modulates motor output to the muscles, ensuring that physical exertion stays within safe limits

brain ensures that you dont exercise until you are completely flat out (death) as muscles would technically allow this to happen

Question 3

serotonin

Answer 3

5HT
involved in feelings of tiredness, mood, sleep, sensory perception, pain, appetite regulation, thermoregulation
implicated in many psychiatric disorders

Question 3

central fatigue

Answer 3

force decline caused by reduction in motor neuron firing frequency, caused by reduced excitatory drive from brain
at fatigue there is loss of ouput from brain, this has an impact on peripheral neurones, reducing their output which reduces their stimulus to muscles
meaning less force can be produced

Question 4

dopamine

Answer 4

DA
important in motivation- reward and attention, arousal and sleep wake cycles
involved in memory, motor control and coordination

Question 5

noradrenaline

Answer 5

implicated in regulation of attention, arousal + sleep wake cycles
learning and memory, anxiety, pain, mood and brain metabolism
increased when body is stressed

Question 6

brain serotonin and fatigue

Answer 6

effect of brain serotonin on central fatigue
- decreases arousal and motivation
- decreased tolerance to pain and discomfort
- increased lethargy and tiredness

Question 7

drug induced performance gains
(studies)

Answer 7

influencing serotonin pathways
- rats running on treadmill
- injected with saline, agonist or antagonist
- endurance time increases with antagonist
- blocked receptor so counteracts serotonin

Question 8

newsholme central fatigue hypothesis

Answer 8

BCAA and central fatigue
leucine
isoleucine
valine
muscles can use BCAA for energy

Question 9

tryptophan and bcaa

Answer 9

blood brain barrier is highly regulated
tyrptophane is an amino acid bound to albumin
BCAA are in blood
trp is a building block of serotonin- if there is lots of serotonin there will be increased central fatigue
(trp enters brain and builds up serotonin)

Question 10

at rest
trp

Answer 10

tryp:bcaa ratio is low
trp and bcaa use same transporter
means BCAA and trp are both transported into brain
not much trp is transported so not much serotonin is produced

Question 11

during exercise
trp

Answer 11

trp: bcaa ratio increases
during exercise there are more FFA
FFA bind to albumin and push out the tryptophan (unload it)
lots more trp in the blood
BCAA may be being used in metabolism
lots of trp and less BCAA transported into brain
lots of serotonin will be produced casuing central fatigue

Question 12

exercise and BCAA supplementation

Answer 12

less trp will be shuttled into the brain meaning less serotonin will be reduced- reducing cnetral fatigue

there is no evidence that this actually works to reduce central fatigue
as there are lots of other factors that can affect central fatigue

Question 13

amphetamines

Answer 13

increase brain dopamine activity

study- running endurance in rats while taking different doses of amphetamines
increasing does does increase endurance time up to an optimum
increasd dose (too much) is not effective

Question 14

brain dopamine and central fatigue

Answer 14

plays an important role in motivation + reward, pleasure, motor control and coordination
dopamine synthesis and metabolism increase during exercise
fatigue coincides with decreased synthesis and metabolism
maintaining brain dopamine synthesis and metabolism delays fatigue

Question 15

tyrosine and dopmaine synthesis

Answer 15

tyrosine is building block of dopamine- transported across blood brain barrier
supplementing with tyrosine will lead to increased dopamine in brain

Question 16

tyrosine supplementation

Answer 16

90 mins cycle exercise followed by time trial
- Placebo, carbohydrate, tyrosine
- Trial to see how quickly they completed a certain distance (longer is worse)
- Carbohydrate decreased the time more than the tyrosine supplementation

Question 17

tyrosine and cognitive function

Answer 17

• Tyrosine supplements taken during exposure to prolonged periods of stress- 1 week combat training course- appears to attenuate decrements in cognitive function
• Decreased error with tyrosine group showing that the tyrosine worked
• Shows tyrosine supplementation worked

Question 18

caffiene and dopamine

Answer 18

caffiene can enhance dopamine release
caffiene has impct on ryanodine receptors in muscle
caffiene can directly facilitate ca2+ release in muscle

Question 19

hypoglycaemia and central fatigue

Answer 19

Rationale- brain is dependent on glucose
glucose from bloodstream is predominant energy source for brain
voluntary muscle activation decreases during hypoglycaemia

reduced performance associated with low blood glucose levels may indicate central fatigue- but it may be due to many other factors (including peripheral fatigue)

Question 20

studies- brain activity

Answer 20

• increased brain activity in hypothalamus immediately after glucose ingestion, also about 10 minutes after
• the second spike is caused when the glucose is actually being absorbed, first ome is when the brain knows that the glucose is coming

Question 21

study- mouth rinse

Answer 21

Glucose mouth rinse- 6.4% carb mix or placebo during 60 mins cycle time trial
- swirling the mouth with the glucose leads to a better time trial
- central fatigue mechanisms seem to kick in later
- glucose didn’t enter the body or get ingested but the brain knew that the glucose was coming which is what caused the better time

Question 22

study- hyperthermia

Answer 22

Cycling at 60% VሶO2max
- Hyperthermia: at 40C, to volitional exhaustion (~50 min) → core temperature (Tc ) = 40.0±0.1C
- Control: at 18C, for 1 hour → Tc = 38±0.1C
- Followed by a 120 second sustained maximum voluntary contraction (MVC) of the quadriceps.

• Electrical stimulation leads to an increased force production that the muscle can do but it is stopped by central fatigue