Aerobic exercise; effects on exercise intensity and duration Flashcards
What is aerobic exercise
Exercise in which the aerobic system is the main energy supply, typically 30 minutes or longer in duration
What substrates are used during aerobic exercise
In aerobic exercise substrates (e.g., carbohydrates and lipids) need be oxidized to produce energy
Fuels are oxidized from several tissues, not just muscle
What are the differences between high intensity and aerobic exercise
In HII Energy derived from anaerobic sources; PCr at very rapid intensities and anaerobic glycolysis
Less energy is derived from intramuscular stores (e.g., glycogen and lipids)
Type II and type IIx ‘fast twitch’ muscle fibres play a more important role
Whereas in aerobic exercise Energy derived from lipids, carbohydrates (and some protein)
Type I ‘slow twitch’ muscle fibres play a more important role
Energy use dependent on intensity
What source is energy mostly derived from at lower intensities
Lipid sources
What source is energy mostly derived from at higher intensities
Carbohydrate sources
When does fat utilisation during exercise peak
At around 65% of VO2max
How can you increase the amount of fat that can be oxidised during exercise
Via training
Why does lipolysis slow at high exercise intensities
1) Reduced blood flow to adipose tissue so as a consequence, free fatty acid delivery to the exercising muscles is inhibited, limiting the oxidation rates
2) the amount of carnitine, which is needed to shuttle FFA into the mitochondria for oxidation is reduced - so it is a transport into the mitochondria issue. As exercise intensity increases, the formation of acyl carnitine is inhibited
Where are the fats used to fuel aerobic exercise are oxidized from
intramuscular triglycerides and adipose tissue
Why is the amount of carnitine reduced during high intensity exercise
Too much Acetyl CoA (from increased glycolysis) inhibits Pyruvate dehydrogenase and this inhibits HI exercise (as less pyruvate converted to ACOA)
To keep PDH going, carnitine will react with ACOA to produce acetyl carnitine instead of Acyl carnitine for the carnitine shuttle
This means less carnitine for beta-oxidation and transport of FA into the mitochondria
So fewer FA can be used for energy production
What is fat max
The percentage at which the muscle uses the maximal amount of fat for oxidation for energy (65% of VO2max)
Why is training to improve fat max beneficial for athletes
Preserve carbohydrate stores for end of exercise to improve performance
Why do trained people have a higher fat oxidation rate
More mitochondria
What happens are fat oxidation decreases
there is an increase in the rate of carbohydrate oxidation
Where do the carbohydrates come from
The carbohydrates come from our glycogen stores in muscle and liver
What enzyme regulates glycogenolysis
Glycogen phosphorylase
What does the regulation of glycogenolysis depend on
Energy status of the cell
How is glycogenolysis regulated to increase with exercise intensity
As exercise intensity increases there is an increased rate of ATP turnover
ATP increases the build up of by products such as ADP, AMP and Pi
These metabolites act as signals to the cell, indicating that more energy is needed.
Thus, glycogenolyis is activated to provide that energy by allosteric control of key regulatory enzyme is glycogen phosphrylase. This is activated by increased ADP, AMP and PI thus increasing glyocgenolysis.
How does increased muscle blood flow also increase carbohydrate oxidation during exercise
Increased plasma glucose uptake to transport from liver to muscle
How does PDH regulate carbohydrate oxidation during exercise
Increase in glycolysis (due to increased exercise intensity) leads to an increase in pyruvate and PDH
PDH catalyses acetyl CoA production which is needed for the TCA cycle
What happens as exercise duration increases
As exercise duration increases there is an increase in fat oxidation
Why do we have to rely on lipolysis during long duration exercise
The longer we exercise, the more our glycogen stores become depleted (hence why we need to keep refuelling in long distance events).
This is also why people consume high carbohydrate diets.
This resulting in a decrease in glyoctic flux, e.g., energy production with glucose as the major provider
This downregulates PDH activity
This means we have to rely on lipolysis for energy e.g., oxidising what we have stored in out adipose tissue and muscle – the latter isn’t much but the former is plentiful.
What are the mechanisms of fatigue
Glycogen depletion, dehydration, blood glucose maintenance
Why is a high carbohydrate diet beneficial to performance
Less glycogen depletion
