lecture 16

Question 1

Oxygen uptake:

Carbon dioxide production:
)

Respiratory exchange ratio (RER)

Answer 1

Oxygen uptake: V̇O2
* A rate (L/min or mL/min)
* Carbon dioxide production: V̇CO2
* A rate (L/min or mL/min)
* Respiratory exchange ratio (RER)
* Carbon dioxide produced / Oxygen consumed
* RER = V̇CO2 / V̇O2

Question 2

RER = V̇CO2 / V̇O2
* If RER = ……, carbohydrate is the fuel
* If RER = ……., lipid is the fuel
* If ….. > RER > ……, the fuel is a mix of carbohydrate and lipid

Answer 2

RER = V̇CO2 / V̇O2
* If RER = 1.0, carbohydrate is the fuel
* If RER = 0.71, lipid is the fuel
* If 1.0 > RER > 0.71, the fuel is a mix of carbohydrate and lipid

Question 3

Why are carbohydrates preferred over fats during high-intensity exercise?

Answer 3

Carbohydrates provide ~7.7% more energy per liter of O₂ than fats (5.05 vs 4.69 kcal/L O₂), making them more oxygen-efficient. When oxygen is limited (high intensity), the body relies more on carbs for energy.

Question 4

What influences substrate oxidation?

Answer 4

1) Exercise intensity
2) Exercise duration
3) Substrate availability
4) Sex
5) Training status

Question 5

Relationship between exercise intensity and fuel use (substrate oxidation)

Answer 5

At rest → low intensity exercise:
Fat (lipids) is the main energy source
Especially plasma free fatty acids (FFA)
At ~60–65% of VO₂max:
Peak fat oxidation occurs
At >60–65% of VO₂max:
Carbohydrates become the dominant fuel
Muscle glycogen use increases
At high intensity (>65% VO₂max):
Fat use decreases significantly
Lipid is used sparingly
Overall concept:
Low intensity → fat
High intensity → carbohydrates

Question 6

at low intensity what kind of fat is used

Answer 6

plama ffa

Question 7

How does diet affect muscle glycogen levels and endurance performance?

Answer 7

Carbohydrate diet: highest glycogen → longest performance (~189 min)

Mixed diet: moderate glycogen → moderate performance (~126 min)

Fat + protein diet: low glycogen (~30%) → shortest performance (~59 min)

Key idea: Higher starting muscle glycogen = greater endurance capacity

Question 8

What are the effects of carbohydrate loading on exercise performance

Answer 8

:

Increases muscle glycogen above normal levels
No effect on:
High-intensity exercise < 5 min

Moderate/low intensity exercise (60–90 min)à

Improves performance in endurance exercise (>90 min):
Delays fatigue by ~20%

Exhaustion is linked to critically low muscle glycogen
Some glycogen still remains at fatigue, but not enough to sustain work

Question 9

How does sex affect substrate oxidation during exercise?

Answer 9

Females have higher fat oxidation during exercise (whole-body)
Lower RER in females → greater reliance on fat
Fat contributes a greater % of energy in females vs males
Males rely relatively more on carbohydrates