Lecture 7: Exercise Flashcards
What is anaerobic exercise?
Anaerobic is high intensity exercise over a short period of time.
• An example is sprinting.
• Dominated by fast twitch (type II) muscle.
• Rapid generation of energy over a short period of time.
• Energy is granted too rapidly for substrates, including oxygen to diffuse into the muscle.
• Cells use their own energy stores of glycogen and phosphocreatine.
What is aerobic exercise?
Aerobic is low intensity exercise over a longer period of time.
• An example is long distance running.
• Energy stores in the muscle are not sufficient.
• We must use glycogen stores in the liver and fat from adipose for oxidation in the muscle.
• It is dominated by slow twitch (type I) muscle fibre.
How does anaerobic exercise work?
Muscle contraction is powered by ATP hydrolysis and the ATP must be replaced rapidly.
• However, measurements of [ATP] in contracting muscles show it to be almost constant.
• Level of ATP is buffered by phosphocreatine.
H+ + ADP + P-CR ATP + CR
• ATP is also sustained by glycolysis, using G6P from glycogen breakdown as opposed to glucose from the blood.
• Flux through the glycolytic pathway increases 1000-fold at the start of intense exercise.
• We can improve our ability to perform anaerobic exercise by building fast twitch muscle (resistance training).
• We can also use creatine supplements in order to have larger PCR supplements.
• We can also ingest sodium hydrogen carbonate. It lessens fatigue by acting as a buffer against lactic acid.
How do muscle tissues signal the upregulation of glycolysis? Draw a diagram.
Nerve impulses are used to upregulate glycogenolysis and glycolysis.
• Calcium signalling is used as a signalling molecule. It integrates upregulation of glycolysis with muscle contraction. There is no need for hormones. It is very fast.
• Glycolysis with glycogen stores produces 3 ATP instead of 2. It skips the hexokinase step.
How does substrate cycling of PFK control its rate?
Substrate cycling is used to amplify a signal.
• Adrenaline upregulates phosphorylase kinase. It primes it.
• Calcium activates calmodulin which activates PK.
What are the effects of fatigue during anaerobic exercise?
Production of lactic acid causes a fall in pH from 7 to 6.5.
• Reduce calcium release by the sarcoplasmic reticulum.
• Impair actin myosin interactions.
• Makes PFK more sensitive to inhibition.
• Impair calcium binding to troponin.
What is aerobic exercise?
Aerobic exercise is low intensity and for extended periods of time.
• The muscle must be supplied with fuel for prolonged periods of time.
• It utilises intra and extracellular fuel.
• Fuels are completely oxidised in order to minimise fatigue (lactic acid build up).
• The muscles must be supplies with substrate and oxygen while carbon dioxide is removed at an increased rate.
• This requires a coordinated change in circulation as well.
How does the body change during aerobic exercise?
- Products anaerobic respiration (lactate and protons) leads to vasodilation.
- This increases blood flow by 100 times.
- A fall in blood pH also triggers changes in respiration to speed up gas exchange.
- The sympathetic nervous system and adrenaline trigger an increase in cardiac output.
- Adrenaline binds to the β adrenergic receptors.
- The somatic nervous system activates contraction and glycogenolysis.
How do hormones change during aerobic exercise?
- Adrenaline, glucagon and cortisol concentrations all rise as part of the stress response.
- Insulin falls due to inhibition of release by adrenaline.
How does carbohydrate metabolism change during exercise?
Glucose oxidation is a major fuel source. We want to supply as much glucose as we can.
• Liver glycogen can sustain the body for under an hour.
• Liver glycogenolysis stimulus is unclear. However, the insulin/glucagon ratio plays a role.
• Muscle glycogen is a factor. Not all of it is used, only the stores in active muscle.
• Muscle glycogenolysis is stimulated by the sympathetic nervous system. Adrenaline also contributes.
• Glycogen overall can support 80-90% of output for 2 hours before performance suffers.
• Hepatic GNG doesn’t supply a significant energy source.
• Almost all the GNG occurring is recycling lactate. It doesn’t give a new source of energy.
• Blood flow to the liver is restricted to the supply of gluconeogenesis substrate is diminished.
• This further contributes to the wall when glycogen stores are depleted.
• Plasma glucose concentrations do not fall. However, turnover is massively increased due to more uptake in muscle stimulated by AMPK.
• Glycogen is very hydrophilic. When stored, it contains 3 x its eight in water. Glycogenolysis therefore requires the release of some of the water lost during exercise as sweat.
How does fat metabolism change during exercise?
Long periods of sustained exercise require glucose and fatty acid oxidation.
• Fatty acids come from muscle TAGs or adipose TAGs.
• As insulin is downregulated, fatty acid mobilisation increases.
• Fatty acids represent a much greater energy store.
• Fatty acid oxidation spares glucose/glycogen according to the Randle cycle.
• We can test this by increasing FA conc in the blood. This is done by using a heparin injection to liberate LPL.
• Fatty acid oxidation may be limited by transport of FAs. During moderate exercise, fatty acid concentration and oxidation are both high. However, during high intensity exercise, fatty acid concentration increases but oxidation does not.
• This may be due to blood flow. FAs may become stuck near adipose tissue.
• When exercise stops, FA in the blood increases but glycerol does not.
