Energy metabolism during exercise

Question 1

Anaerobic ATP fuel

Answer 1

Phosphocreatine

• Fastest source for ATP
• Few ATP production

Glycogen

• Fast source
• Generates lactic acid

Question 2

Creatine phosphate

Answer 2

Fastest fuel for ATP
- First source of ATP in muscle

This source can only last up to around 16 seconds.
- Muscle only has a limited capacity for storage.

Forms ATP via creatine kinase:
Creatine phosphate + ADP —–> ATP + Creatine.

Question 3

Skeletal muscle blood flow

Answer 3

During extreme physical exertion, 80% of CO is directed to skeletal muscle.

Skeletal muscle pump enhances blood flow by propelling blood in the veins.

Adrenaline acts on beta-2 receptors on BVs to stimulate vasodilation.

Question 4

General metabolism during exercise

Answer 4

Initially creatine-phosphate is source of ATP.

Then glycogenolysis provides fuel
- Increase in O2 consumption increases ATP generated.

When oxygen supply decreases, glycolysis happens anaerobically
- Produce lactate and less ATP

Question 5

Factors that affect blood flow to muscles

Answer 5

NO acts on vascular smooth muscles
- Increases vasodilation

Beta-2 adrenergic causes vasodilation in vascular smooth muscles .

Question 6

Cori cycle

Answer 6

The utilisation of lactate:

When lactate is made in the muscle via anaerobic glycolysis, it is transported to the liver.

In the liver, it undergoes gluconeogenesis to release glucose.

Glucose is transported back to the muscle to regenerate energy.

This is more sufficient when blood flow is very good.

Question 7

Fatigue

Answer 7

Occurs when rate of ATP utilisation exceeds ATP synthesis.

Lactic acid build up also decreases the force generated when the muscle contracts due to low pH.

Question 8

Regulation of glycogen metabolism during exercise

Answer 8

Contraction stimulates:

• Glycogenolysis
• Glycolysis

Ca2+ stimulates:

• Muscle contaction
• Activation of glycogen phosphorylase

Question 9

Ca2+ in muscle contraction [3]

Answer 9

Increase in intracellular Ca2+ signal for muscle contraction.

Ca2+ also activates glycogen phosphorylase which increases muscle glycogen breakdown.

Ca2+ stimulates NO production = increased blood flow via vasodilation.

Question 10

Regulation of phosphorylase during exercise

Answer 10

Activated by:

• AMP
• Phosphorylation in relation to Ca2+ and hormones (adrenaline, cortisol)

Question 11

Regulation of synthase during exercise

Answer 11

Activated by:
- G-6-P (low in exercise)

Inactivated by:
- Phosphorylation by Ca2+, stress hormones

Question 12

Regulation of PFK-1 during exercise

Answer 12

Inhibited by:
- ATP

Activated by:

• AMP
• Fruc-2,6-phosphate

Question 13

Fatty acid metabolism during exercise

Answer 13

Fatty acids oxidised to generate energy.

Dependent to oxygen supply.

Question 14

Resting muscle metabolism

Answer 14

Glycogen stores are replenished in the muscle.

Muscles use the oxidation of fatty acids to generate energy.

Question 15

Metabolism whilst sprinting

Answer 15

• Catecholamines (ADR, NDR) stimulates glycogen breakdown anaerobically.
• Phosphocreatine used to generate ATP.
• Muscles rely on anaerobic energy production as blood vessels are compressed during muscle contraction
• Blood glucose maintained from lactate by the liver.

Question 16

Middle distance metabolism

Answer 16

Middle distance use aerobic oxidation to make up around 30% of ATP requirement.
- Oxymyoglobin provides some O2

Anaerobic glycolysis accounts for the majority of ATP generation.

Creatine-phosphate contributes very little at 800m and almost not at all at 1500m.

Question 17

Marathon Stage 1 metabolism (rest)

Answer 17

When the muscle is resting, it uses fatty acid oxidation to provide energy.

Glycogen stores in the liver and muscle are maintained.

Question 18

Marathon Stage 2 metabolism (10 mins)

Answer 18

Glycolysis:
- Muscle glycogen and liver glucose supply fuel for energy

Glycogenolysis:
- Stimulated by AMP and adrenaline increase

Gluconeogenesis from fatty acids by the liver
- Stimulated by adrenaline

Question 19

Marathon Stage 3 metabolism (2 hours)

Answer 19

Most of the liver’s glycogen is used up.

Insulin:glucagon ratio falls significantly= gluconeogenesis heavily stimulated:

• Body uses FAs as main source of energy
• Ketone bodies used for energy

FAs can only generate 50% maximum power output.

Question 20

Lipid usage dependance on carbs

Answer 20

FA breakdown is dependent on continual glycogen metabolism
- Can only occur when oxaloacetate is available from Kreb’s cycle

• Pyruvate from glycolysis maintains oxaloacetate levels

Question 21

Marathon stage 4 metabolism

Answer 21

Muscle and liver glycogen finished

State of hypoglycaemia reached:

• Lactic acidosis
• Exhaustion
• Loss of cognitive function