S2, L4: Anaerobic energy provision

What are the reactions from ATP that release energy? (4)

• ATP + H₂O —> ADP + P_i

• ADP + H₂O —> AMP + P_i

• ATP + H₂O —> AMP + PP_i

• PP_i + H₂O —> 2P_i

How is energy for muscle contraction generated?

ATP hydrolysation by myofibrillar ATPase

How large are ATP stores in the muscle?

ATP storage in the muscle is very limited with roughly 2 seconds worth of maximal contractions

What happens if ATP is not regenerated and why?

• Rigor mortis

• The myosin head is ATPase, so an ATP molecule must be bound to it in order to break a cross-bridge

Describe the ATP-PCr system

• The recycling of ATP during exercise until phosphocreatine stores are used up

• Energy release from PCr cannot be used for cellular work, so it is used to resynthesise ATP

Describe the relationship between (a) muscle phosphocreatine concentration, (b) ATP concentration and exercise duration

a. Phosphocreatine concentration has a negative linear relationship with exercise duration

b. ATP concentration is maintained at a relatively stable level until after 125% of VO_{2 max}

What are the benefits of creatine supplementation? (2)

• Causes a delay in ADP concentration increases

• Slowly improves cross-bridge cycling

What is a disadvantage of creatine supplementation?

• Creatine intake has osmotic consequences

• There is higher cell water content, which can lead to weight gain

What is the equation for the myokinase reaction?

ADP + ADP —> ATP + AMP

When does the myokinase reaction occur?

Only during high intensity exercise, activated when pH falls

What does AMP do?

AMP is an activator of enzymes involved in glycogen breakdown

What is the ATP yield of the anaerobic glycolytic system?

• 2-3 ATP per mol of substrate

• 1-1.5 ATP per mol of lactate if all pyruvate is converted to lactate

Describe the functions of phosphofructokinase (PFK), succinate dehydrogenase (SDH), and citrate synthase

• PFK - rate limiting enzyme in glycolysis, converting fructose 6-phosphate to fructose 1,6-bisphosphate

• SDH - krebs cycle enzyme that bridges the krebs cycle and electron transport chain

• Citrate synthase - catalyses the first, rate-limiting step of the krebs cycle, condensation of acetyl CoA and oxaloacetate to form citrate

How does creatine kinase regulate the rate of ATP production?

• Via a negative feedback system

• When ATP decreases and ADP increases, creatine kinase activity increases

• When ATP increases, creatine kinase activity decreases

How does phosphofructokinase limit the rate of the glycolytic system?

• When ATP decreases and ADP increases, PFK activity increases

• When ATP increases, PFK activity decreases

Other than ATP, what is PFK regulated by?

Products of the TCA cycle

How do different types of training affect enzyme activity?

• In aerobically trained individuals, activity of succinate dehydrogenase, malate dehydrogenase, phosphorylase, and carnitine palmityl transferase are significantly higher

• In anaerobically trained individuals, activity of creatine kinase, myokinase, and phosphofructokinase are significantly higher

What is power (for ATP production)?

The rate at which ATP can be produced

What is capacity (for ATP production)?

The quality of ATP that can be produced

What is a Wingate test?

A 30 second all out sprint on a cycle ergometer at a load of roughly 7.5% of body mass to determine peak power and fatigue index

How is fatigue index calculated?

Fatigue index (%) = [(peak power - lowest power)/peak power] x 100

How are the different energy systems used during the Wingate test?

• ATP-PCr system - highest proportion in the first 2.5 seconds, 30% at 7.5 seconds and minimal from 12.5 seconds onwards

• Glycolytic system - highly used from 12.5 seconds onwards

• Aerobic system - some use from 12.5 seconds onwards

Why are the ATP-PCr and glycolytic systems predominant in the Wingate test? (2)

• Fast energy - many ATP per time

• Metabolic inertia - aerobic metabolism is slower to start due to the time taken for oxygen to reach the muscles

How is anaerobic energy expenditure calculated?

• Using a pre- and post-exercise muscle biopsy

• Contribution of anaerobic energy = -2(change in ATP) - 1(change in PCr) + 1.5 (change in lactate) + 1.5 (change in pyruvate)