Energy metabolism during exercise

Question 1

What is the main fuel for ATP in muscle?

Answer 1

Glycogen

Question 2

How long does the ATP last for in the muscle?

Answer 2

4 seconds

Question 3

List the 3 systems forming ATP in muscle stating whether they are anaerobic or aerobic

Answer 3

Anaerobic- ATP-PC and lactic acid

Aerobic- Oxygen system

Question 4

Describe the importance of creatine phosphate

Answer 4

First top-up source for muscle ATP
During vigorous contraction this lasts approx 16 secs
May be enough for a 100-200 metre sprint

Question 5

Which enzyme breaks down creatine phosphate?

Answer 5

Creatine kinase

Question 6

Give the equation for creatine phosphate breakdown

Answer 6

Creatine phosphate + ADP —-> ATP + Creatine —-> ATP + Pi —–> creatine phosphate +ADP

Question 7

Describe the characteristics of skeletal muscle blood flow

Answer 7

Skeletal muscle accounts for about 20% of cardiac output at rest; can increase to more than 80% during extreme physical exertion.

Coordinated, rhythmical contractions (e.g. running) enhance blood flow by means of the skeletal muscle pump mechanism.

Vascular β2-adrenoceptors result in vasodilation when stimulated by agonists such as adrenaline

Blood flow is strongly determined by local regulatory (tissue and endothelial) factors such as tissue hypoxia, adenosine, K+, CO2, H+, and nitric oxide

Question 8

What is the fuel source for exercise?

Answer 8

Glycogenolysis provides fuel source

Question 9

What determines the amount of energy derived from glycolysis and respiration?

Answer 9

Amount of energy derived from glycolysis and respiration dependent on the intensity and duration of the exercise

Question 10

What happens to oxygen consumption and blood flow during exercise?

Answer 10

Increase in O2 consumption for ox phos

Increased blood flow to muscles due to local mediators (NO) and β-adrenergic stimulation of vascular smooth muscles

Question 11

What happens if the oxygen supply decreases?

Answer 11

If the increased rate of metabolism outstrips the oxygen supply, glycolysis can proceed anaerobically
Much less ATP is produced and lactate builds up
Even when the oxygen supply is sufficient, pyruvate may be formed faster than it can be oxidised. This also causes the accumulation of lactate

Question 12

What is the cori cycle?

Answer 12

Lactate is used by the liver to regenerate glucose which can be transferred back to the muscle for energy production. If there is insufficient blood flow, lactic acid builds up in the muscle.

Question 13

What is fatigue and describe how it occurs?

Answer 13

Inability to maintain desired power output

Occurs when rate of ATP utilization exceeds its rate of synthesis

Accumulation of pyruvate and lactic acid in the contracting muscle result in a decline in force generated

Due to decrease in muscle pH

Question 14

Describe the effect of calcium ions on contraction

Answer 14

Muscle contraction is associated with increase in Ca2+ concentration within the muscle cells
Increase in Ca2+ activates glycogen phosphorylase
Increase in Ca2+ concentration is the signal for muscle contraction
Also increases muscle glycogen breakdown to supply the energy required
Stimulates the production of nitric oxide which causes vasodilation of the blood vessels and increased blood flow

Question 15

In addition to glycogen, what else is used by the muscle for energy?

Answer 15

In addition to glycogen, muscle also uses fatty acids derived from the diet or adipose tissue to maintain ATP levels.
However fatty acid oxidation is aerobic and dependent on an adequate oxygen supply

Question 16

What occurs during resting muscle metabolism?

Answer 16

In resting muscle, glycogen stores are maintained/replenished

Oxidative metabolism of fatty acids provides energy for the muscle

Question 17

Describe the fuels used as time of exercise increases

Answer 17

Only 2 fuels are used in short sprints to replenish ATP, phosphocreatine and anaerobic glycogen breakdown to lactate
As the distance increases, phosphocreatine levels are exhausted and the muscle relies solely on glycogen breakdown either anaerobically to lactate or aerobically to CO2 via the TCA cycle
During the marathon, the muscle are reliant entirely on oxidative metabolism of glycogen and also glucose and fatty acids coming from the liver and adipose tissue

Question 18

Describe the metabolism during a sprint

Answer 18

Catecholamines stimulate glycogen breakdown in muscle which is converted anaerobically to lactate. Phosphocreatine is converted to creatine with the transfer of Pi to ADP to form ATP
Blood vessels are compressed during sprinting isolating the cells from the blood supply making the muscles reliant on anaerobic energy production from glycogen
Large quantities of lactic acid produced as glycolysis proceeds which the liver can use to maintain blood glucose levels via gluconeogenesis

Question 19

Describe the metabolism during middle distance

Answer 19

Large quantities of lactic acid produced as glycolysis proceeds which the liver can use to maintain blood glucose levels via gluconeogenesis
Lactate is still a major end product of glycogen metabolism contributing 65% of the ATP required
The contribution of phosphocreatine to the ATP required becomes less and less as the distance increases. At 800 metres it contributes 5% and essentially zero over 1500 metres

Question 20

Describe the metabolism during the resting state of a marathon

Answer 20

Resting state- In resting muscle and liver, glycogen stores are maintained. Muscle uses aerobic oxidation of fatty acids to provide the energy it requires.

Question 21

Describe the metabolism during the first 10 minutes of a marathon

Answer 21

10 Minutes- Muscle glycogen and glucose from the liver are used to power muscles, mainly through glycolysis. Increased vasodilation in the muscles increases O2 supply increasing the aerobic glycogen utilisation and ATP production.
Glycogen breakdown stimulated by increased AMP and adrenaline release
Fatty acids are mobilised by the release of adrenalin to allow liver to maintain blood glucose levels by the provision of energy and the glycerol backbone

Question 22

Describe the metabolism during 2 hours of a marathon

Answer 22

2 hours- A marathon requires 700g of glycogen, whereas muscle and liver contain only 500g, therefore this is largely depleted after 20 miles. Blood glucose falls significantly, about 90% of liver glycogen used. Insulin levels fall and glucagon secretion increased.
Body switches to fatty acids as main source of energy. Only generates sufficient ATP for 50% of maximum power output and pace falls off as glycogen depleted – known as ‘hitting the wall’. Ketone bodies may also be used. Lactate, glycerol and muscle amino acids used to support glucose production by the liver, energy being derived from fatty acid oxidation.

Question 23

What is meant by lipids burn in a carbohydrate flame?

Answer 23

Carbohydrates are needed. Just having lipids is not enough
Fatty acid breakdown depends in part on a continual background level of glycogen metabolism
Fatty acid catabolism continues only if sufficient oxaloacetate is available for the Kreb’s cycle
Pyruvate formation during glucose metabolism plays important role in maintaining oxaloacetate levels

Question 24

Describe the metabolism at the finish of the marathon

Answer 24

Muscle and liver glycogen are depleted
Hypoglycaemia with typical symptoms of confusion, lack of cognitive function, lactic acidosis and exhaustion may occur (less likely with training)