Energy metabolism during exercise Flashcards
What is the main fuel for ATP in muscle?
Glycogen
How long does the ATP last for in the muscle?
4 seconds
List the 3 systems forming ATP in muscle stating whether they are anaerobic or aerobic
Anaerobic- ATP-PC and lactic acid
Aerobic- Oxygen system
Describe the importance of creatine phosphate
First top-up source for muscle ATP
During vigorous contraction this lasts approx 16 secs
May be enough for a 100-200 metre sprint
Which enzyme breaks down creatine phosphate?
Creatine kinase
Give the equation for creatine phosphate breakdown
Creatine phosphate + ADP —-> ATP + Creatine —-> ATP + Pi —–> creatine phosphate +ADP
Describe the characteristics of skeletal muscle blood flow
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
What is the fuel source for exercise?
Glycogenolysis provides fuel source
What determines the amount of energy derived from glycolysis and respiration?
Amount of energy derived from glycolysis and respiration dependent on the intensity and duration of the exercise
What happens to oxygen consumption and blood flow during exercise?
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
What happens if the oxygen supply decreases?
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
What is the cori cycle?
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.
What is fatigue and describe how it occurs?
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
Describe the effect of calcium ions on contraction
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
In addition to glycogen, what else is used by the muscle for energy?
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
What occurs during resting muscle metabolism?
In resting muscle, glycogen stores are maintained/replenished
Oxidative metabolism of fatty acids provides energy for the muscle
Describe the fuels used as time of exercise increases
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
Describe the metabolism during a sprint
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
Describe the metabolism during middle distance
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
Describe the metabolism during the resting state of a marathon
Resting state- In resting muscle and liver, glycogen stores are maintained. Muscle uses aerobic oxidation of fatty acids to provide the energy it requires.
Describe the metabolism during the first 10 minutes of a marathon
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
Describe the metabolism during 2 hours of a marathon
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.
What is meant by lipids burn in a carbohydrate flame?
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
Describe the metabolism at the finish of the marathon
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)
