L2. Fuel Selection During Exercise Flashcards
LO
- Outline the effect of the muscle glucose utilisation on blood glucose levels to hormonal responses
- Predict the effect of the low insulin and high glucagon on target tissues and blood fuel levels.
- Explain why glucose needs to be recycled and describe how this is achieved.
- Recognise what catabolic pathways change as fatty acids become available during low intenstity exercise.
- Describe the general pattern of fuel oxidation in gentle exercise.
- Predict the effect of increasng the pace of gentle exercise.
- Compare the pattern of fuel utilisation in moderate exercise with that in gentle exercise.
- Describe the changes to fatty acid oxidation that occur when an athlete changes from gentle to strenuous exercise
- Explain the circumstances under which muscle glycogen is mobilised.
- Outline the pattern of fuel utilisation in strenuous exercise.
- State the importance of glycogen to the competitive athlete
Muscle Contraction
- Uses ATP
- Actin and myosin interact (filaments slide across eachother)
- At rest muscle still uses ATP to maintain ion and concentration gradients (sarcoplasmic reticulum and Ca2+)
Muscle cell types
Type 1 - Red, slow:
- Comtracts slower
- Many mitochondria
- Good blood supply
Type 2b - White, fast:
- Rapid contraction
- Few mitochondria
- Poor blood supply
- Packed with contractile filaments
Stategies of fuel oxidation: Stage 1
Burn either FA, Glucose, or Amino Acids
FA:
1. Beta oxidation
2. 2-C Acetate
3. Carried on CoA
Glucose:
1. Pyruvate
2. 2-C Acetate
3. Carried on CoA
Amino Acids:
1. Many pathways
2. 2. 2-C Acetate
3. Carried on CoA
Stategies of fuel oxidation: Stage 2
Acetyl-CoA
- Krebs cycle substrate
- Producing CO2 and H/e-
Coupling
- ATP stores are very low
- MUST generate as it is being used
Rates: Synthesis = Used
Gentle Exercise
- Increase rate of ATP production/ synthesis through greater ADP availability
- Dissipate proton gradient
- Increase in ETC
- Fuel oxidation can increase
- Glucose or FA will be burnt
- FA concentrations are low in body
- In gentle exercise muscle usually use glucose as fuel as it is most readily availible.
Glucose as fuel
System is all Demand Driven
- Krebs cycle demans acetyl-CoA
- More Acetyl = demand for Pyruvate
- More Pyruvate = more glucose
- Glucose transporters move to the cell surface to bring glucose into the cell
- Glucose is phosphorylated by a kinase inside the cell and turned into 2x pyruvate
- PDH enzyme (Pyruvate dehydrogenase) converts the pyruvate into Acetyl-CoA
- Blood glucose levels lower
- Glucose homeostasis (insulin production stops, glucagon production starts)
Effects of low insulin and high glucagon
- Liver releases glycogen stores as glucose into blood stream
- WAP (fat cells) break down triglycerides into FA and release into blood stream
Gentle exercies on Blood glucose
- Body demands more ATP
- Cells take in glucose as it is most readily availible and converted into Acetyl-CoA for Krebs cycle
- Blood glucose drops
- Insuline production stops and glucagon production starts
- Liver cells release glucose from Glycogen stores
- WAP release FA from triglycerides
- FA can undergo beta-oxidation and converted into Acetyl-CoA for krebs cycle
Glucose recycling
- Glucose (glycogen) stores are limited
- FA substitute for glucose as fuel
- FA prevent wasteful glucose oxidation as brain needs it
- As Acetyl-CoA build up occurs more than the kreb cycle demands, PDH enzyme (Pyruvate dehydrogenase) will be inhibitted from converting pyruvate into Acetyl-CoA
- Lacate is then built up when pyruvate is not turned into Ac-CoA
- Lactate can be reprocessed into glucose in the liver.
Gentle exercise summary
- Initially glucose is used as fuel
- After several minutes, FA takes over as fuel
- Glucose still gets into the muscle, but is converted to lactate
- lactate goes to the liver to be ‘recycled’ into glucose via Gluconeogenesis
Moderate exercise (jogging)
- As pace increases, more FA burn, but a maximum is reached as enzymes work at a slow pace
- Therefore FA oxidation cannot maintain ATP production alone
- The Krebs cycle will increase its demand for ac-CoA and match its demand for the build up of ac-CoA
- PDH inhibition stops
- With PDH inhibition gone, pyruvate can be catalysed to ac-CoA and entre the krebs cycle
- Therefore a micture of glucose and FA used during exercise, glucose stores come from the liver.
Strenuous exercise
- Limited speen on oxidation of FA and blood glucose
- Rate of supply and transport in blood can’t keep up with demand
- Muscle glycogen is then blocen down for fuel
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Very Strenuous exercise
- ATP production cannot be met by oxidative phosphorylation alone
- Uses glycolysis for an extra 2x ATP (very fast)
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Why glycogen is important
- When glycogen has run out, only FA oxidation can be used for ATP generation
- Power output is lower when using only FA (cannot sprint if there is no glycogen)
Sprinting
- Uses type 2b muscle fibres
- Very rapid consumption of ATP
- Can NOT use FA (poor O2 supply and low mitochondria in 2b fibres)
- Can NOT use bloog glucose (poor fuel supply with little blood supply, delay in transporter recruitment with little blood supply)
Glycolysis to lactate is very fast but creates a problem:
- LOTS of lactate built up in the muscle quickly with little blood supply to take it away
Creatine Phosphate is an instant store of ATP
Creatine Phosphate + ADP = Creatine + ATP
Conclusion
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