substrate utilisation

Question 1

what are the methods to assess fuel use

Answer 1

indirect calorimetry (most common)
arterial and venous blood sampling during exercise (invasive)
muscle biopsies before and after exercise (invasive)
stable isotopes (uncommon)

Question 2

how does indirect calorimetry work

Answer 2

measures pulmonary gas exchange
O2 uptake and CO2 production
(can estimate amount of fat and carb used)

Question 3

how does blood sampling work

Answer 3

can determine energy utilisation based on blood glucose, O2, or CO2 in blood

Question 4

how do muscle biopsies work

Answer 4

measures changes in substrate concen such as muscle glycogen and intramuscular triglycerides

Question 5

how do stable isotopes work

Answer 5

add isotopes to blood stream before collection to label glycogen and glucose
- see how much of the isotopes are left to measure utilisation

Question 6

what is the respiratory exchange ratio

Answer 6

CO2 produced / O2 consumed
VCO2/VO2

Question 7

what do different RER values mean

Answer 7

RER = 1 → carb = fuel
RER = 0.71 → lipid = fuel
Between 0.71-1 = mix of carbs and lipids as fuel

Question 8

what is the difference in energy between carbs and lipids

Answer 8

7.7% more energy per unit of O2 for carb vs lipid

Question 9

what are the 5 aspects that affect subtrate utilisation

Answer 9

• exercise intensity
• exercise duration
• substrate availability
• sex
• training status

Question 10

at what intensities is fat (plasma FFA) oxidation the predominant energy source

Answer 10

resting state to exercise at 60-65%

Question 11

at what intensities is carb oxidation the predominant energy source

Answer 11

exercise >60-65% VO2 max
(lipids used sparingly)

Question 12

what does glycogen content of the working muscle determine

Answer 12

capacity to perform long and heavy exercise

Question 13

how do different diets affect cycling time

Answer 13

protein + fat = 56 min
mixed = 126 min
carb = 189 min
(correlation with initial glycogen content)

Question 14

what is carb loading

Answer 14

elevating pre exercise muscle glycogen contents above normal resting levels

Question 15

what is the effect of carb loading

Answer 15

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)

Question 16

what is the ideal carb diet

Answer 16

train low carb
compete high carb

can’t continue low carb forever because body will lose enzymes needed to use carbs

Question 17

what is the difference in oxidation between males and females

Answer 17

higher amounts of fat oxidation during exercise in females at the whole body level (all exercise intensities)

males = more glycolytic

Question 18

what is the difference in RER between males and females

Answer 18

males = higher RER (rely more on carbs)
females = lower RER (rely more on fat)

Question 19

what is the difference in RER between trained and untrained individuals

Answer 19

trained = lower RER (rely more on fat metabolism due to higher mito density)
untrained = higher RER (larger glucose uptake - rely more on glycolysis)

Question 20

what is the difference in substrate utilisation between trained and untrained individuals

Answer 20

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)

Question 21

what is the difference in lactate between trained and untrained

Answer 21

higher levels in untrained
- signal that more glycolysis happens compared to oxidative metabolism

Question 22

what is the advantage of lipid oxidation

Answer 22

2.17 times (per unit of weight) greater energy yield per gram of lipid vs carbs