L2.3 CHO metabolism during exercise

Question 1

What is the fate of pyruvate?

Answer 1

Pyruvate is oxidised in mitochondria (aerobic), or into lactate (anaerobic and reversible)

*Glucose phosphorylation is irreversible*

Question 2

What is the effect of the duration & intensity on the rate of glycogen breakdown?

Answer 2

↑exercise → ↑rate of glycogen breakdown
↑duration → ↓rate of glycogen breakdown

Question 3

What are the factors regulating glycogenolysis?

Answer 3

• Ca2+, Pi (↑ATP breakdown → ↑Pi →+feedback) → activates glycogen phosphorylase → ↑glycogen breakdown
• Adrenaline (signals mobilisation of glycogen stores)
• Muscle glycogen stores (↑capacity → ↑breakdown)
• FFA → influences glycogen breakdown (↑FFA → ↓glycogen breakdown)
• ↑Temperature → ↑breakdown

Question 4

What are the effects of training CHO metabolism?

Answer 4

• ↑muscle glycogen levels
• ↓glycogen reliance (less breakdown → lactate)
• ↑ATP turnover

Question 5

How does increase exercise intensity and duration affect glucose uptake?

Answer 5

↑exercise & duration → ↑glucose uptake (due to ↑muscle blood flow)

Question 6

What are the 3 points of regulation for glucose uptake?

Answer 6

1) SUPPLY: by the diffusion gradient ([glucose] in blood & muscles)
2) TRANSPORT: GLUT 4 transports
3) Metabolism: by hexokinase enzyme (*Glycogen synthase activated in recovery)

Question 7

What is the purpose of liver glucose output?

And how is it achieved?

Answer 7

• to maintain blood glucose levels
• Closely matched with glucose uptake
• Finite capacity of liver to produce glucose
  
  • ∴ Well maintained in the short term, but falls in the long term.

Produces glucose by breakdown of glycogen (mainly), some AA, glycerol, pyruvate, lactate

Question 8

How is liver glucose output regulated?

Answer 8

• Feedforward and back mechanism (connection between CNS & liver glucose output)
• Insulin & glucagon
• Liver [glycogen]
• ↑Blood [glucose] → ↓[glycogen] breakdown
• Adrenaline & sympathetic nerves → slightly redundant/small control
• Many control mechanisms with redundancies → shows importance of process.

Question 9

What is the effect of training on CHO metabolism?

Answer 9

↓uptake, ↓oxidation, ↓GNG, ↓GGL → able to exercise at a higher intensity

Question 10

What is the effect of pyruvate dehydrogenase (PDH)?

Answer 10

It is the rate limiting step, ↑exercise → ↑PDH → ∴↑CHO metabolism

Question 11

Relationship between power and lactate usage?

Answer 11

↑power → ↑lactate exponentially

Question 12

How is lactate regulated?

Answer 12

• In muscles: balance btw rates of pyruvate formation & oxidation
• In blood: rates of lactate production and clearance (liver clears lactate)
• Muscle oxidative capacity (↑mito→↑capacity→↑lactate oxidation)
• LDH isoenzymes (greater affinity for pyruvate → ↑lactate)
• O2 supply to contracting muscles (↓O2 → ↑lactate)
• Adrenaline & muscle glycogen (↑Adrenaline & glycogen breakdown → ↑lactate)

Question 13

What is the effect of training on lactate?

Answer 13

• ↓muscle & blood lactate
• ↑MCT 1 (transporters for lactate) → able to oxidise more lactate