9. Fatigue in Prolonged Endurance Exercise Slides

Question 1

Fatigue – definition

Answer 1

exhaustion, the moment at which exercise ceases

Question 2

Why do we fatigue?

Answer 2

A mechanism that aims to maintain the physiological integrity of the body
* Signals arising from several systems are integrated in the brain during exercise
to stop physical exertion/ reduce intensity,
as a safety mechanism to prevent the limit of physiological adjustments being exceeded, in systems involved in the exercise

Question 3

what is Peripheral fatigue produced by

Answer 3

changes at or distal to the neuromuscular junction

Question 4

what is central fatigue

Answer 4

reduction in neural drive to the muscle

Question 5

Causes of Fatigue in Prolonged
Exercise:

Answer 5

• Peripheral Fatigue
  – Glycogen depletion
  – Increased core temperature (impaired thermoregulation in the heat)
  – Dehydration
• Central Fatigue
  – Increased serotonin

Question 6

Peripheral fatigue: Glycogen
Depletion

Answer 6

Fatigue coincides with low muscle
glycogen concentration

Question 7

Glycogen Depletion

Answer 7

• Performance can be prolonged by
  exogenous carbohydrate feeding

Question 8

Effect of Carbohydrate Feeding on
Time to Fatigue

Answer 8

• Delayed fatigue with glucose consumption
• Glycogen stores not spared
• Continued exercise relies on plasma glucose

Question 9

Effect of Ambient Temperature on
Fatigue

Answer 9

cooler temp = longer exercise ability

Question 10

Dehydration

Answer 10

loss of water equivalent to 2 % of body mass consistently leads to a reduction in endurance performance

• Especially if exercise duration
  > 90 min
  – Reduced sweating and skin blood flow
  – Reduced heat dissipation
  – Can lead to heat illness

Question 11

Increased Cardiovascular
Strain with Progressive
Dehydration

Answer 11

↑ heart rate
↓ stroke volume
↓ cardiac output
↑ a-v O2 difference

Question 12

Increased Serotonin

Answer 12

• Serotonin (neurotransmitter)
  – 5-hydroxytryptamine (5-HT)
  – Promotes sleep and tiredness
• Increased 5-HT in exercise is associated with fatigue

Question 13

what is 5-HT made from where is it available, what does it bind to

Answer 13

tryptophan (amino acid)
plasma
albumin (plasma protein), as are fatty acids

Question 14

what does 5-HT do

Answer 14

Crosses blood-brain barrier by specific transporter
– Branched chain amino acids (BCAA) utilise same transporter as TRP

Question 15

Prolonged Exercise

Answer 15

– ↑ Plasma fatty acids
– Displace tryptophan from albumin
– ↑ free tryptophan (f-TRP)
– ↑ muscle uptake of BCAA
–>↑ f-TRP/BCAA
–> ↑ TRP entry to brain
–>↑ 5-HT production

Question 16

Peripheral Fatigue summary

Answer 16

• Fatigue at high intensity not due to glycogen depletion.
• can prolong performance with use of exogenous CHO
• Hotter ambient temperature and core body temperature = faster fatigue.
• Dehydration impairs performance.

Question 17

Central Fatigue summary

Answer 17

• More free tryptophan available due to displacement of tryptophan from albumin due to increase in plasma fatty acids.
• Increase BCAAs into muscle.
• Increase in tryptophan into brain.
• Increase in 5-hydroxytryptamine (5-HT) synthesis