T2 L9 Energy metabolism during exercise

Question 1

How much can muscle increase its rate of ATP production in the short term?

Answer 1

By 20-100 fold

Question 2

How much ATP does the muscle have at rest?

Answer 2

27mmol of ATP per kg dry weight

During vigorous contraction this lasts for 4 seconds

Question 3

List the 3 systems that form ATP in muscle from fastest to slowest

Answer 3

ATP-PC
Lactic acid - glycolysis
Oxygen system - oxidative phosphorylation

Question 4

What is the fuel used by the ATP-PC system?

Answer 4

Phosphocreatine

Question 5

What is the fuel used by the lactic acid (glycolysis) system?

Answer 5

Glycogen

Question 6

What is the fuel used by the oxygen system (oxidative phosphorylation)?

Answer 6

Glycogen
Fats
Proteins
O2 is required

Question 7

List the 3 systems that form ATP in muscle from the most ATP produced to the least.

Answer 7

Oxygen system - many, unlimited ATP
Lactic acid
ATP-PC

Question 8

What is creatine phosphate?

Answer 8

First top up source for muscle ATP
Creatine can be reversible phosphorylated to create creatine phosphate
Creatine phosphate breaks down to form creatinine which is excreted in the urine

Question 9

How much creatine phosphate is stored in the muscle at rest?

Answer 9

Muscle has 100mmol creatine phosphate per kg dry

Lasts for 16 seconds so may be enough for 100-200m sprint

Question 10

Skeletal muscle accounts for how much of cardiac output at rest and during vigorous exercise?

Answer 10

20% at rest

80% during extreme physical exertion

Question 11

What are vascular beta 2 adrenoceptors?

Answer 11

Stimulated by agonists such as adrenaline which leads to vasodilation

Question 12

What factors determine blood flow?

Answer 12

Local regulatory factors
Tissue hypoxia
Adenosine
K+
CO2
H+
Nitric oxide

Question 13

What increases blood flow to muscles during energy metabolism during exercise?

Answer 13

Local mediators - nitric oxide

Beta-adrenergic stimulation of vascular smooth muscle

Question 14

What is the amount of energy derived from glucose & respiration dependent on?

Answer 14

The intensity & duration of exercise

Question 15

What happens if the rate of metabolism exceeds the oxygen supply?

Answer 15

Glycolysis occurs anaerobically

Much less ATP is produced & lactate builds up

Question 16

What causes an accumulation of lactate when oxygen supply is plentiful?

Answer 16

Pyruvate is formed faster than it can be oxidised which causes an accumulation of lactate

Question 17

Why does lactic acid decrease pH?

Answer 17

It dissociates into a lactate ion & protein at a physiological pH which decreases pH

Question 18

What is the Cori cycle?

Answer 18

Pathway where lactate is used by the liver to regenerate glucose which is transferred back t the muscle for energy production.

Question 19

What is fatigue?

Answer 19

Inability to maintain desired power output
Occurs when the rate of ATP utilisation exceeds its rate of synthesis
Accumulation of pyruvate & lactic acid in the contracting muscle lead to a decline in the force generated.

Question 20

What does an increase in calcium ions do to glycogen phosphorylase?

Answer 20

It activates it.

Question 21

What is the role of calcium ions in muscle contraction?

Answer 21

The increase in Ca2+ concentration signals muscle contraction & increases muscle glycogen breakdown to supply the energy required.
Stimulates production of nitric oxide which causes vasodilation of blood vessels & increased blood flow

Question 22

How is phosphorylase activated?

Answer 22

By AMP which acts allosterically

Activated by phosphorylation in response to a stress hormones, increased cytoplasmic calcium ions.

Question 23

How is glycogen synthase activated?

Answer 23

Allosterically by glucose-6-phosphate which is low during exercise

Question 24

How is glycogen synthase inactivated?

Answer 24

By phosphorylation in response to stress hormones, increased calcium ions

Question 25

How is phosphofructokinase-1 inhibited?

Answer 25

Allosterically by ATP & activated by AMP & Fru-2,6-P | Important sensor of energy availability & needs during exercise

Question 26

What are the 2 fuels used in short sprints to replenish ATP?

Answer 26

Phosphocreatine | Anaerobic glycogen breakdown to lactate

Question 27

What does the muscle rely on as distance increases & phosphocreatine levels are exhausted?

Answer 27

Glycogen breakdown anaerobically or aerobically via TCA cycle.

Question 28

What are the muscles reliant on during a marathon?

Answer 28

Oxidative metabolism of glycogen, glucose & fatty acids from the liver & adipose tissue.

Question 29

Describe metabolism whilst sprinting

Answer 29

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

Question 30

Describe metabolism for middle distance

Answer 30

Aerobic oxidation of glycogen makes up 30% of ATP required to support contraction. Some of oxygen may come from oxymyoglobin in the muscle. Lactate is still a major end product of glycogen metabolism - contributes 65% of the ATP required. Contribution of phosphocreatine to ATP required becomes less as distance increases.

Question 31

Describe stage 1 of a marathon

Answer 31

In the resting muscle & liver the glycogen stores are maintained. Muscle uses aerobic oxidation of fatty acids to provide the energy it requires.

Question 32

Describe stage 2 of a marathon

Answer 32

First 10 minutes Muscle glycogen & glucose from the liver are used to power muscles mainly through glycolysis. Increased vasodilation in the muscles increases oxygen supply, which increases aerobic glycogen utilisation & ATP production. Glycogen breakdown is stimulated by increased AMP & adrenaline release Fatty acids are mobilised by the release of adrenaline to allow the liver to maintain blood glucose levels by provision of energy & glycerol backbone.

Question 33

Describe stage 3 of a marathon

Answer 33

After 2 hours Blood glucose falls as 90% of liver glycogen is used Insulin levels fall & glucagon secretion increases. Body switches to fatty acids as the main source of energy - only generates enough ATP for 50% of maximum power output. Lactate, glycerol & muscle amino acids are used to support glucose production by the liver.

Question 34

How much glycogen does a marathon require?

Answer 34

700g | Muscle & liver contain 500g which runs out after 20 miles

Question 35

Describe stage 4 of a marathon

Answer 35

Finish Muscle & liver glycogen are depleted Hypoglycaemia - less likely to with training.

Question 36

What are the symptoms of hypoglycaemia?

Answer 36

Confusion Lack of cognitive function Lactic acidosis Exhaustion