Excercise phys

Question 1

What’s going on in exercise concerning carbohydrate metabolism?

Answer 1

• 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

Question 2

What energy source is preferred at high exercise intensity vs. low-moderate exercise intensity?

Answer 2

• Fat at the moderate-low
  
  • Glucose from glycogen at high intensity
  • Cut-off is about 60% of VO2max

Question 3

What are the main hormones in dictating a shift to or from CHO metabolism in exercise?

Answer 3

• 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

Question 4

What are the local factors in the skeletal muscles that start shifting the cell towards CHO preference?

Answer 4

• Increased overall calcium from high intensity depolarization
  
  • Activates glycogen phosphorylase
  • Also, more contraction means more GLUT-4 to the membrane

Question 5

Describe the overall process of getting the energy rich triglycerides from adipose tissue to muscle for utility in endurance exercise

Answer 5

• 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

Question 6

What stores of fat do the muscle cells themselves have?

Answer 6

• Small lipid droplets called intramuscular triglycerides (IMTG)
  
  • Stored in the cytoplasm of skelatal muscle cells close to mitochondria
  • Analogous to glycogen, but are fat

Question 7

Does amino acid metabolism play a role in exercise?

Answer 7

• 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

Question 8

What is important about the increasing acidosis seen in lactate build-up?

Answer 8

• 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

Question 9

What are the important training adaptations to substrate utilization in the athlete?

Answer 9

• 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

Question 10

What is the main takeway from cellular levels of training and accommodation in the athlete?

Answer 10

• 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