L4.1 Oxygen Consumption

Question 1

What is oxygen deficiency?

Answer 1

• O2 supply levels ↑progressively, suboptimal of demands
• PCr used during the suboptimal period of O2 deficiency, (and some glycolysis but not much)
• Switches to glycolysis at optimal O2 supply

Question 2

What is the delay in O2 uptake due to?

Answer 2

• 1) Delay in O2 transport (takes time for capillaries to open up, for O2 to diffuse from RBC into mitochondria)
• 2) Metabolic inertia (Mitochondria not working optimally yet)
  
  • Mito enz slugglish, takes time to ↑/work optimally

Question 3

What are the 3 determinants of VO2 kinetics?

Answer 3

• 1) Ca2+ activation of mitochondrial dehydrogenase & ATP synthase
• 2) [ATP]/[ADP], [PI] & [NAD+]/[NADH]
• 3) Mitochondrial PO2

Question 4

Effect of exercise on O2 uptake?

Answer 4

• ↑exercise → ↑O2 uptake (linear relationship), plateaus at VO2 max

Question 5

What is VO2 drift?

Answer 5

VO2 drift - slight constant increase of VO2 max.

• 80% drift results from active muscles
• ↑duration → recruits more type 2 fibres (less efficient)
• ↓P-O coupling (oxidative phosphorylation) efficiency
• ↑muscle temperature
• ↑catecholamines
• O2 cost of ventilation and cardiac work

Question 6

During recovery, there is an excess post oxygen consumption (EPOC).

What occurs during EPOC?

Answer 6

• Resyn of ATP & PCr (fast phase)
• Restoration of myoglobin O2 stores
• Elevated HR, VE, temperature & hormone (O2 consumption still higher) (slow phase)
• ↑FFA metabolism (rely more on fat metabolism, resyn glycogen), still needs extra O2
• Mitochondrial ‘uncoupling’ enzyme (↓P-O coupling efficiency)
• Glycogen resyn

Question 7

Regeneration of PCr?

Answer 7

• Rapid (t1/2 = 60-90s)
• O2 dependent
• Influenced by muscle oxidative capacity
  
  • ↑capacity → ↑speed of recovery
• Creatine supplements → ↑PCr resyn & stores

Question 8

Muscle glycogen resynthesis?

Answer 8

• Activation of glycogen synthase (↑after exercise)
• Depletion of glycogen stores → ↑ activation of GS
• ↑GLUT 4 → ↑resyn
• Damage muscle fibres → damages GLUT 4, insulin binding

Question 9

What is glycogen super compensation?

Answer 9

• Basis for carbo-loading
• Depletion of glycogen → over compensates of glycogen after rest + CHO ingestion
  
  • resultant resting glycogen = higher

Question 10

What is the specific dynamic action of food?

Answer 10

• Uses energy to digest nutrients, ↑after exercise
• Recovery → eat → ↑O2 uptake

Question 11

What is the fate of lactate?

Answer 11

• Oxidation in skeletal & cardiac muscle (mostly in type 1 slow twitch)
  
  • MCT 1 transports it into muscle fibres → oxidise
  • Lactate → pyruvate → oxidised (reversible reaction)
• Substrate of glycogen synthesis
• ↑lactate does not cause ↑O2 consumption post exercise
• Active recovery → ↑lactate removal