substrate utilisation Flashcards
what are the methods to assess fuel use
indirect calorimetry (most common)
arterial and venous blood sampling during exercise (invasive)
muscle biopsies before and after exercise (invasive)
stable isotopes (uncommon)
how does indirect calorimetry work
measures pulmonary gas exchange
O2 uptake and CO2 production
(can estimate amount of fat and carb used)
how does blood sampling work
can determine energy utilisation based on blood glucose, O2, or CO2 in blood
how do muscle biopsies work
measures changes in substrate concen such as muscle glycogen and intramuscular triglycerides
how do stable isotopes work
add isotopes to blood stream before collection to label glycogen and glucose
- see how much of the isotopes are left to measure utilisation
what is the respiratory exchange ratio
CO2 produced / O2 consumed
VCO2/VO2
what do different RER values mean
RER = 1 → carb = fuel
RER = 0.71 → lipid = fuel
Between 0.71-1 = mix of carbs and lipids as fuel
what is the difference in energy between carbs and lipids
7.7% more energy per unit of O2 for carb vs lipid
what are the 5 aspects that affect subtrate utilisation
- exercise intensity
- exercise duration
- substrate availability
- sex
- training status
at what intensities is fat (plasma FFA) oxidation the predominant energy source
resting state to exercise at 60-65%
at what intensities is carb oxidation the predominant energy source
exercise >60-65% VO2 max
(lipids used sparingly)
what does glycogen content of the working muscle determine
capacity to perform long and heavy exercise
how do different diets affect cycling time
protein + fat = 56 min
mixed = 126 min
carb = 189 min
(correlation with initial glycogen content)
what is carb loading
elevating pre exercise muscle glycogen contents above normal resting levels
what is the effect of carb loading
high intensity exercise <5 min = no effect (low carb contribution at this intensity)
moderate intensity exercise (20-35% VO2max) 60-90min = no effect (low carb contribution at this intensity)
exercise @ 60-65% VO2max >90 min = postpones fatigue (postpones carb depletion - contributor to fatigue)
what is the ideal carb diet
train low carb
compete high carb
can’t continue low carb forever because body will lose enzymes needed to use carbs
what is the difference in oxidation between males and females
higher amounts of fat oxidation during exercise in females at the whole body level (all exercise intensities)
males = more glycolytic
what is the difference in RER between males and females
males = higher RER (rely more on carbs)
females = lower RER (rely more on fat)
what is the difference in RER between trained and untrained individuals
trained = lower RER (rely more on fat metabolism due to higher mito density)
untrained = higher RER (larger glucose uptake - rely more on glycolysis)
what is the difference in substrate utilisation between trained and untrained individuals
trained derive a lower % of energy from carb fuel sources (glycogen, glucose, lactate)
trained derives a greater % of energy from lipid energy sources (plasma FFA and intramuscular triglycerides)
what is the difference in lactate between trained and untrained
higher levels in untrained
- signal that more glycolysis happens compared to oxidative metabolism
what is the advantage of lipid oxidation
2.17 times (per unit of weight) greater energy yield per gram of lipid vs carbs
