Week 2 - Exercise Metabolism Contd. Flashcards
Energy yield of
a) CHO
b) Fats
a) 4kcal/g
b) 9kcal/g
Key term for glycogen breakdown
glycogenolysis
Define RER and the two conditions for RER.
measurement of pulmonary gas exchange which provides a non-invasive technique to estimate fuel utilization during exercise
R = VCO2/VO2
1) Measurement must be performed during steady-state exercise
2) Assumes that 0 protein is used as a fuel during exercise
Two factors governing fuel selection during exercise
1) Exercise intensity
2) Exercise duration
Define the ‘Crossover’ concept and explain what this is due to?
the shift from fat to CHO metabolism as exercise intensity increases.
Due to recruitment of fast-twitch muscle fibers and increasing blood levels of epinephrine stimulate glycolysis and lactate production (inhibits fat metabolism).
How does increased exercise duration influence the rate of lipolysis?
There is an increases in the breakdown of triglycerides into glycerol and FFA.
It’s stimulated by rising blood levels of several hormones (epinephrine, norepinephrine and glucagon).
What is the effect of glycogen depletion during prolonged high intensity exercise?
Decreases rate of glycolysis and production of pyruvate which is an important precursor for Krebs-cycle, therefore there is a decrease in the rate of Kreb-cycle activity.
FATmax.
Highest rate of fat oxidation (60% V02max) that is reached just before lactate threshold.
Lactate threshold
the point at which blood lactic acid rises systematically during incremental exercise
> Appears at 50-60% V02max untrained individuals
Appears at 65-80% VO2max trained individuals
Onset of Blood Lactate Accumulation (OBLA)
Point at which blood lactate reaches more than 4mmol/l
Explanations for the lactate threshold
1) Low muscle oxygen (hypoxia) therefore increase anaerobic metabolism
2) Reduced rate of lactate removal from the blood: blood flow to muscle prioritized over liver that is responsible for removing lactate
3) Accelerate glycolysis due to epinephrine: NADH produced faster than it is shuttled to mitochondria therefore pyruvate accepts un-shuttled H+ to form lactate (and NAD+).
4) Recruitment of fast-twitch fibers: LDH isozyme in fast fibers had greater affinity for attaching to pyruvate which promotes lactate formation
How can lactate be used as a fuel source during exercise?
Cori cycle - lactate produced in the muscle is transported to the liver where it can be converted back to glucose (gluconeogenesis) and this is then carried back in the blood to the skeletal muscle cells to be reused in the glycolytic pathway.
