Excercise phys Flashcards
What’s going on in exercise concerning carbohydrate metabolism?
• Super important during high exercise intensity where it is the predominant energy source for skelatal muscle
• Glycogen is the storage form of glucose and CHO
• 80% of CHO is stored in skelatal muscle while 14% is in liver
• Glycogen breakdown to glucose-1-P by glycogen phosphorylase
○ Stimulation = muscle contraction and catecholamine action
• 60% exercise intensity raises peripheral muscle uptake of glucose to 80% from 20%
○ Important here to note that skeletal muscle gets glucose greedy during exercise
• Glycogen is very important for athletes
• People with a problem in phosphorylase enzyme suck as athletes
What energy source is preferred at high exercise intensity vs. low-moderate exercise intensity?
- Fat at the moderate-low
- Glucose from glycogen at high intensity
- Cut-off is about 60% of VO2max
What are the main hormones in dictating a shift to or from CHO metabolism in exercise?
• CHO = carbohydrate
• Cortisol and epinephrine
• Beta-adrenergic activity increases with exercise intensity with the release of epinephrine from the adrenal medulla being directly proportional to exercise intensity
• Epinephrine stimulates muscle glycogenolysis by increasing phosphorylase activity thus it is a major regulator of CHO metabolism during exercies
• Availability of FFA during exercise is also closely regulated by epinephrine
○ Stimulates the activity of hormone sensitive lipase
• At high intensity exercise
○ Epinephrine may reduce blood flow to adipose tissue and lead to a reduction in FFA to muscles
What are the local factors in the skeletal muscles that start shifting the cell towards CHO preference?
- Increased overall calcium from high intensity depolarization
- Activates glycogen phosphorylase
- Also, more contraction means more GLUT-4 to the membrane
Describe the overall process of getting the energy rich triglycerides from adipose tissue to muscle for utility in endurance exercise
• Hormone Sensitive Lipase is important for freeing the Fatty Acids from the triglyceride stores in the adipocytes
• The other product of this is glycerol
• Hormonal control is epi and norepi
• Catecholamines bind to beta and alpha2 receptors on the adipocyte to increase cAMP and ultimately phosphorylate HSL
○ Phosph-HSL means increased lipolysis
○ Remember that very high intensities means inhibitory from lowered bloodflow to adipose tissue
• Insulin will drop a bit during exercise to remove inhibition of lipolysis
• FFA must be transported to skelatal muscle
• S-FABP = sarcolemmal fatty acid binding protein
○ One of the transport proteins in the muscle cell that helps bring FA out of the circulation and into the muscle cell for utilization as energy
• FFA in the cytosol must be activated to fatty acyl-CoA ester
• FFA is attached to CoA and that forms fatty acyl-CoA which is then transported through OMM b CPT-1
• Inside mitochondrial matrix is where the beta oxidation takes place and fatty acyl-CoA is degraded to acetyl CoA which can then enter TCA
• Produces NADH and FADH2 for ATP production in ETC
What stores of fat do the muscle cells themselves have?
- Small lipid droplets called intramuscular triglycerides (IMTG)
- Stored in the cytoplasm of skelatal muscle cells close to mitochondria
- Analogous to glycogen, but are fat
Does amino acid metabolism play a role in exercise?
- Yes, though only about 10% of the energy comes from them
- When glycogen levels are low amino acids play a larger role
- Alanine is important as it is glucogenic
- Synthesized in muscle and sent to liver to be converted to glucose through glucose-alanine cycle
- Branched chain amino acids may also play an important part during exercise
- Leucine, isoleucine and valine make up the BCAA
- Leucine is ketogenic
- Isoleucine is both ketogenic and glucogenic
- Valine is glucogenic
- BCAA tend to be primarily utilized, which can lead to muscle breakdown in high intensity, endurance exercise
- Thus, supplementation can help
What is important about the increasing acidosis seen in lactate build-up?
- Lactate formation releases an H+
- Also, ATP hydrolysis leads to pH changes
- Essentially, really busy muscle cells get acidotic
- This decreases peak twitch force, maxiumum shortening velocity and a ATPase reduciton in myosin
What are the important training adaptations to substrate utilization in the athlete?
• After training, glycolytic flux is decreased at same relative intensities
• There is a decrease in glycogenolysis and therefore a reduction of energy requirements derived from glucose
• Blood lactate accumulation can be lower in highly trained athletes
○ Higher level of lactate oxidation
• Decrease in blood lactate levels observed after training as well as a lower glucose utilization and higher fat utilization
• The increase in mitochondrial density increases the oxidation of cytosolic pyruvate via pyruvate dehydrogenase
○ End result is increased lactate clearance capacity through an increase in mitochondrial lactate dehydrogenase
- Specific lactate transporters - MCTS (metacarboxylates) will facilitate lactate transport in and out of the muscle cell better in trained individuals
- MCT1 in type 1 fibers, or oxidative fibers, and training can increase these lactate transporters
- MCT4 is expressed mainly in glycolytic fibers and are involved in lactate transport out of the cell from glycolytic fibers to more oxidative fibers
- Increasing training will lead to increasing mitochondrial density which will mean better fat utilization
What is the main takeway from cellular levels of training and accommodation in the athlete?
- Lactate clearance is increased.
- through transport of lactate more efficiently out of cell or into cell depending on MCT1 (into the oxidative cell) or MCT4 (out of the glycolytic cell)
*mitochondrial density is increased, therefore fat utilization is also increased
