Aerobic and Anaerobic Metabolism

Question 1

What are energy generating pathways?

Answer 1

• resynthesis of ATP is optimised for different activities by utilisng different energy systems
• these vary in maximal rates and also sustainability

Question 2

What is the process of anaerobic metabolism in muscle?

Answer 2

• under aerobic conditions, glucose catabolism yields NADH to fuel high rates of ATP synthesis via oxidative phosphorylation
• at high exercise intensities, the NADH:NAD+ ratio increases and the electron transport chain can’t regenerate NAD+ quick enough to maintain glycolysis
• as NADH is the product and NAD+ the reactant, many metabolic enzymes are inhibited by the accumulating NADH-
• under those anaerobic conditions, lactate is produced from pyruvate via lactate dehydrogenase in turn regenerating NAD+
• muscle and blood can increase 1 to 30 mmolkg-1 during maximal exercise

Question 3

What is the process of lactate utilisation in muscle?

Answer 3

• lactate production is associated with muscle fatigue and soreness during hard exercise as muscle H+ production increases and cytosolic pH drops, but is not a cause
• lactate leaves active muscle fibres down a gradient, entering less active muscles fibres, in turn reforming pyruvate

Question 4

What is the process of lactate utilisation in muscle?

Answer 4

• lactate production is associated with muscle fatigue and soreness during hard exercise as muscle H+ production increases and cytosolic pH drops, but is not a cause
• lactate leaves active muscle fibres down a gradient, entering less active muscles fibres, in turn reforming pyruvate
• pyruvate can then be re-oxidised in less active muscle fibres to yield 14 ATP molecules via the pathways we have already discussed

Question 5

What is the process of lactate utilisation in the liver?

Answer 5

• liver glycogen is a source of glucose during exercise
• during prolonged periods of exercise, carbon skeletons from other molecules can be used to synthesise glucose for energy provision in muscle in a process called gluconeogenesis
• lactate can leave fatiguing muscle, enter the liver via the blood and reform pyruvate. pyruvate is then used as a substrate for gluconeogenesis and glucose shuttled back to fatiguing muscle fibres

Question 6

What are the ATP resynthesis rates during intense exercise?

Answer 6

• PCr system: 2.6 mmol.kg.sec-1 (0-7 seconds)
• anaerobic CHO: 1.5 mmpl.kg.sec-1 (5-60 seconds)
• aerobic CHO: 0.5 mmol.kg.sec-1 (>60 seconds)