Fat & Carbohydrate Exercise Physiology Flashcards Preview

DEMS: Unit II > Fat & Carbohydrate Exercise Physiology > Flashcards

Flashcards in Fat & Carbohydrate Exercise Physiology Deck (6)
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Fuel use based on exercise intensity: high vs. low intensity

  • Fat and carbohydrate (CHO) generate ATP during aerobic exercise. Depending on the level of fitness of an individual, fat can sustain the biggest part of ATP production.
  • At low exercise intensities fat is the preferred substrate although there is always some glucose oxidation.  Used when VO2 max is up to 75%                           
  • CHO metabolism is of great importance during exercise, especially during high exercise intensity where it is the predominant energy substrate for skeletal muscle.  Used when VO2 max >75%.



Mechanism of metabolism used in muscles during very high intensity exercise

  • When exercise intensities are very high/close to maximal (above 100% of VO2 max) ATP cannot be generated by the aerobic mechanism
  • ATP generated through the anaerobic mechanism also called substrate level phosphorylation
  • ATP synthesis derived from CHO is much faster and therefore the choice of substrate by skeletal muscle fibers during faster twitch, high exercise intensities.


Metabolic adaptations caused by training

  • After training = ↓ work intensity, ↓ glycolytic flux, ↓ glycogenolysis, ↓ energy requirement from glucose
  • In trained individuals, higher exercise intensities cause lower  blood lactate accumulation due to increased lactate clearance capacity through an increase in mitochondrial lactate dehydrogenase (mLDH)
  • Mitochondrial density and oxidative enzymes increase with training and this increases the capacity for fat utilization.
    • Endurance training can double the mitochondrial capacity to oxidize FFA and pyruvate.


Importance of glycogen for exercise

  • Muscle glycogen is crucial for ATP synthesis during exercise.
  • Proper glycogen storages are of great importance for athletic performance.
  • Multiple studies show that fatigue and decrease in performance is often associated with glycogen depletion and that athletes who have low carbohydrate diets or low glycogen storages 


Role of lactate during exercise

  • Lactic acid is the byproduct of glycolysis. 
  • During competitive exercise ATP generation demands increase and glucose becomes the predominant muscle substrate for ATP generation.
    • The higher the glucose flux into the cell the higher the lactate production.
  • Lactate production is necessary for the continuation of glycolysis
  • Lactate is an important carbohydrate source and a main gluconeogenic precursor during exercise as it is shuttled to other cells, tissues and organs where about 75-80% is oxidized to pyruvate for energy purposes.
  • Lactate accumulation inhibits lipolysis at high exercise intensities → similar to ↑ epi.


Fitness testing parameters

  • VO2 max is meaningless. Average athletes can have higher than pros.
  • Muscle lactate metabolism is much more useful and can subdivide beginners and pros from amount of lactate produced with increasing exercise workload.