W1 L2 fuel selection during exercise

• Fuels


  • Fats
  • Glucose
  • Proteins
  • Acetyl CoA
  • A mixture of everything

  
• Muscle contraction

  • Muscle contraction uses ATP
  • Actin and myosin interaction
  • Filaments sliding across each other
  • The faster the contraction, the faster the use of ATP
  • Even at rest, muscle is using ATP to maintain ion gradients and sarcoplasmic reticulum and Ca2+
• Muscle Cell Types

  • Type I - "Red", "Slow"
  • Type IIb - "White", "Fast"
• Strategy of Fuel Oxidation: Stage 1

  1. Rip hydrogens/electrons (H/e-) out of fuels

  2. Fuels break up into two-carbon chunks
• Strategy of Fuel Oxidation: Phase 2

  1. Rip hydrogens/electrons (H/e-) out of acetate

  2. Complete oxidation of carbon atoms to CO2
• If a cell STOPPED doing work

  • ADP increases
  • Rate of proton movement into the matrix increases
  • Regeneration of H/e- carriers decreases
  • Fuel oxidation and oxygen consumption decreases
• Cells can't burn fuel without doing work
• ATP stores are very low, have to generate it AS IT IS BEING USED
• The rate of ATP synthesis EXACTLY matched to the rate of ATP use
• ATP turnover is very high in relation to stores even at rest
• Gentle Exercise

  1. Elevate the rate of ATP generation

  2. Increase ATP synthase

  3. Dissipate the proton gradient

  4. Increase electron transport

  5. Increase availability of H/e- strippers

  6. Increase fuel oxidation
• Major Pathways of Fuel Oxidation

  • Glycolysis
  • Beta-oxidation
  • Krebs Cycle
• Decrease in blood glucose


  Gives big hormonal responses (Insulin down, Glucagon up)

  
• Effects of Low Insulin and High Glucagon

  1. Stimulation of glycogen breakdown in liver

  2. Stimulation of fat breakdown in white adipose tissue
• Glucose stores (glycogen) are limited, and we cannot convert fatty acids into glucose

  
• Fatty acids substitute for glucose as a fuel, preventing glucose from being wastefully oxidised

  
• PDH inhibited by build up of Ac-CoA


  Pyruvate goes to lactate
• Moderate Exercise

  1. Fatty acid utilisation increases but enzymes reach maximum capacity

  2. Inhibition on glucose oxidation is removed

  3. Glucose oxidation occurs, less glucose recycling, liver glycogen stores depleted faster

  
• Acetyl CoA used faster than made from FA


  PDH NOT inhibited by build up of Acetyl CoA
• Moderate Exercise

  1. A mixture of fatty acid oxidation and glucose oxidation

  2. The glucose comes from the liver

  3. Any further increase in pace met by increase in glucose oxidation

  4. Fatty acid oxidation going at full speed already

  
• PDH

  Pyruvate dehydrogenase
• PDH inhibited by build up of Ac-CoA


  Pyruvate goes to lactate and back to liver
• PDH NOT inhibited by build up of Acetyl CoA
• Moderate Exercise

  • A mixture of fatty acid oxidation and glucose oxidation
  • The glucose comes from the liver
  • Any further increase in pace met by increase in glucose oxidation
  • Fatty acid oxidation going at full speed already

  
• Strenuous Exercise

  • Now limits on speed of oxidation of blood glucose
  • Rate of supply and transport from blood can't keep up
  • Fatty acids still going as fast as they can!
  • So, muscle glycogen now broken down
• Very Strenuous Exercise

  • Now rate of ATP production can't be met by oxidative phosphorylation alone
  • Mitochondrial processes too slow
  • Need to top up with extra boost from glycolysis
  • Remember glycolysis VERY fast
  • Very inefficient
  • Now blood lactate levels will rise
  • Glucose must come from muscle glycogen
  • Transport already at max!

  
• When glycogen has run out, only fatty acid oxidation can be used for ATP generation
• Power output is lower when using only fatty acids
• Cannot sprint if there's no glycogen
• Sprinting

  • Uses Type IIb muscles
  • Poor blood supply
  • Packed full of contractile filaments
  • Few mitochondria
  • VERY rapid consumption of ATP
  • Use Fatty acids? NO!
  • Use Blood Glucose? NO!

  
• Glycolysis to lactate


  1. Very fast but creates a problem

  2. Regeneration of H/e carrier (NAD)

  3. ATP generation is so inefficient

  4. Only 2 ATP per glucose (vs >30 if oxidized to CO2)

  5. So, LOTS of lactate produced very quickly

  6. And a very poor blood supply to take it away
• Creatine Phosphate (CP)


  1. An instant store of ATP

  2. But less than five seconds supply (15 mM)

  3. Creatine supplements boost CP levels!
• You must know the rules of COUPLING
• The rise and fall of glucose and fatty acid oxidation at different intensities

  
• The generally reciprocal relationship between glucose and fatty acid oxidation

  
• The importance of endogenous fuels – and getting rid of waste
• Effect of training
• Changes due to fitness and lack thereof
• Strategies for avoiding fatigue
• Pre- and post-competition nutritional strategy