Energy metabolism during exercise

Question 1

Anaerobic ATP-PC system for forming ATP

Answer 1

Fuel: phosphocreatine

O2 required: no

Speed: fastest

Relative ATP production: few; limited

Question 2

Anaerobic lactic acid system for forming ATP

Answer 2

Fuel: glycogen

O2 required: no

Speed: fast

Relative ATP production: few; limited

Question 3

Aerobic oxygen system for forming ATP

Answer 3

Fuel: glycogen, fats, proteins

O2 required: yes

Speed: slow

Relative ATP production: many; unlimited

Question 4

Creatine phosphate

Answer 4

First top up source for muscle ATP

At rest, 100 mmol creatine phosphate per kg dry weight

Lasts 16 seconds during vigorous exercise

May be enough for 100-200m sprint

Question 5

Characteristics of skeletal muscle blood flow

Answer 5

Accounts for 20% cardiac output at rest; can increase to more than 80% during extreme physical exertion

Coordinated rhythmical contractions enhance blood flow by means of skeletal muscle pump mechanism

Vascular B2- adrenoreceptors result in vasodilation when stimulated by agonists such as adrenaline

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

Question 6

Energy metabolism during exercise

Answer 6

Glycogenolysis provides fuel source

Increase in O2 consumption for ox phos

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

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

Question 7

The cori cycle

Answer 7

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 8

Fatigue

Answer 8

Inability to maintain desired power output

Occurs when rate of ATP utilisation 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 9

Regulation of glycogen metabolism

Answer 9

Glycogen breakdown and glycolysis are greatly stimulated during contraction

Muscle contraction is associated with increase in Ca2+ concentration within the muscle cells

Increase in Ca2+ activates glycogen phosphorylase

Question 10

The role of Ca2+ in muscle contraction

Answer 10

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 11

Resting muscle metabolism

Answer 11

Glycogen stores are maintained/ replenished

Oxidative metabolism of fatty acids provides energy for the muscle

Question 12

Energy utilisation during exercise

Answer 12

Only 2 fuels are used in short sprints: PCr and anaerobic glycogen breakdown to lactate

As distance increases, PCr exhausted and muscle relies on glycogen breakdown anaerobically to lactate or aerobically to CO2 via the TCA cycle

During marathon, reliant on oxidative metabolism of glycogen and also glucose and fatty acids coming from the liver and adipose tissue

Question 13

Metabolism whilst sprinting

Answer 13

Catecholamines stimulate glycogen breakdown, converted anaerobically to lactate; PCr converted to Cr with transfer of Pi to ADP to form ATP

Blood vessels are compressed, isolating cells from blood supply making muscles reliant on anaerobic energy production rom glycogen

Large quantities of lactic acid produced as glycolysis proceeds which the liver can use to maintain blood glucose levels via gluconeogenesis

Question 14

Middle distance metabolism

Answer 14

Distance increases, aerobic oxidation of glycogen makes up 30% ATP required to support contraction; some may come from oxymyoglobin in the muscle

Lactate still major end product of glycogen metabolism contributing 65% ATP required

Contribution PCr becomes less and less; at 800m contributes 5%; 1500m essentially 0%

Question 15

Marathon stage 1

Answer 15

In resting muscle and liver, glycogen stores are maintained

Muscle uses aerobic oxidation of fatty acids to provide the energy it requires

Question 16

Marathon stage 2

Answer 16

10 minutes

Muscle glycogen and glucose from liver used to power muscles through glycolysis

Increases vasodilation in muscles increases O2 supply, increasing aerobic glycogen utilisation

Glycogen breakdown stimulated by increased AMP and adrenaline release

Fatty acids mobilsed by release of adrenaline to allow liver to maintain blood glucose levels by provision of energy and the glycerol backbone

Question 17

Marathon stage 3

Answer 17

2 hours

Marathon requires 700g glycogen, muscle and liver only contain 500g, so largerly depleted of 20 miles

Blood glucose falls, about 90% liver glcyogen used

Insulin levels fall and glucagon secretion increased

Body switches to fatty acid; generates sufficient ATP for 50% of maximum power output

Ketone bodies also used

Lactate, glycerol and muscle amino acids support glucose production by liver

Question 18

Lipids burn in a carbohydrate flame

Answer 18

Fatty acid breakdown depends on continual background level of glycogen metabolism

Fatty acid catabolism continues only if sufficient oxaloacetate is availavle for Kreb’s cycle

Pyruvate formation during glucose metabolism plays important role in maintaining oxaloacetate levels

Question 19

Marathon stage 4

Answer 19

The finish

Muscle and liver glycogen are depleted

Hypoglycaemia with typical symptoms of confusion, lack of cognitive function, lactic acidosis and exhaustion may occur