16. Metabolism During Exercise

Question 1

What is TEA? What % of daily energy needs does this comprise? How variable is it?

Answer 1

• Thermic Effect of Activity
• 15-50% of daily energy needs
• Largest potential variable, day to day

Question 2

What is EPOC? What % of daily energy needs does it comprise?

Answer 2

• Excess postexercise oxygen consumption
• Recovery O2 consumption in excess of resting O2 consumption
• Less than 1% of daily energy needs

Question 3

What is TEF? What % of daily energy needs does it comprise?

Answer 3

• Thermic Energy of Feeding
• “It takes calories to absorb calories”
• 10% of daily energy need

Question 4

Direct vs. Indirect Calorimetry. What does each measure? How different are they from each other?

Answer 4

DIRECT:
-kcals/min of heat flux in a water-perfused room
-measures the actual heat production to determine the body’s rate of energy expenditure
INDIRECT:
-VO2 L/min x Known Fuel Mix = Kcals/min
-measures oxygen consumption to infer the rate of heat production and thereby the body’s energy expenditure
-captures short-term kinetics
**less than 1% diff

Question 5

What is calorimetry?

Answer 5

Measurement of energy expenditure

Question 6

What does heat of combustion refer to? What does it represent?

Answer 6

• Refers to heat liberated by oxidizing a specific food

- Represents the food’s total energy value

Question 7

What is the heat of combustion for 1 g of CHOs? Lipids? Proteins?

Answer 7

• CHOs = 4.2 kcal
• Lipids = 9.4 kcal
• Proteins = 5.65 kcal

Question 8

How is the rate of oxygen uptake (VO2) obtained during indirect calorimetry?

Answer 8

From measurements of expired ventilation and fractions of expired O2 and CO2, assuming no change in body stores of O2, CO2, and N2

Question 9

What is RQ? What does it reflect?

Answer 9

• Respiratory Quotient
• # of moles of CO2 produced per mole of O2 consumed
• Reflects oxidative metabolism at the cellular level

Question 10

What is RER? What does it measure?

Answer 10

• Respiratory Exchange Ratio

- Measures rates of O2 consumed and CO2 produced using expired air measured at mouth

Question 11

What is the relation between RQ and RER?

Answer 11

RQ = RER under steady state conditions

Question 12

Metabolic responses to work onset are a consequence of:

Answer 12

• Rate limits of each metabolic pathway

- Recruitment patterns of motor units

Question 13

When does oxygen uptake occur relative to the onset of work?

Answer 13

Oxygen uptake follows the onset of work

Question 14

What is oxygen deficit? When does it occur?

Answer 14

• Applies to the lag in oxygen uptake at the beginning of exercise
• Diff between O2 actually consumed during exercise and the actual energy requirement & expenditure of exercise
• Occurs during exercise when energy demand can’t be met solely by mitochondrial ATP generation

Question 15

What is does steady state look like on a graph? What does it reflect?

Answer 15

• The plateau

- Reflects a balance between energy required by the working muscle and the ATP production in aerobic metabolism

Question 16

What fuels the O2 deficit?

Answer 16

• Phosphagens
• Anaerobic glycolysis
• O2 stored in hemoglobin & myoglobin

Question 17

What does the magnitude of the O2 deficit depend on?

Answer 17

• Intensity of exercise
• State of training
• Dieting
• Warmup

Question 18

How does the size and rate of EPOC vary in light, moderate, and hard exercise?

Answer 18

Increases in size and rate w/ increased intensity of exercise

Question 19

What are some reasons why oxygen consumption may be elevated following exercise?

Answer 19

LOOKUP

Question 20

What substrates are being metabolized or regenerated following exercise?

Answer 20

LOOKUP

Question 21

What is maximal oxygen consumption (VO2 max)?

Answer 21

• Measure of aerobic capacity for fitness

- Max amount of O2 that an individual can utilize during intense exercise

Question 22

If a person doesn’t reach a physiologic plateau in their VO2 before fatigue, their highest VO2 is called what?

Answer 22

Peak VO2 = symptom-limited VO2max

Question 23

What is the criteria for VO2max?

Answer 23

• RER >/= 1.1
• [lactate] > 8 mmol/L
• HR approx. 220-age
• RPE >/= 15 (very hard)

Question 24

What type of athletic performance does VO2max predict?

Answer 24

Aerobic capacity for fitness

Question 25

What is lactate threshold? Where is this point on a blood lactate vs. exercise workload graph?

Answer 25

• Point at which lactate entry into blood exceeds its removal
• On graph: inflection upward on exponential increase

Question 26

List 4 potential factors that lead to the exponential increase in lactate accumulation at high workload.

Answer 26

• Low muscle oxygen tension
• Accelerated glycolysis (increase in pyruvate conc)
• Reduced rate of lactate removal relative to lactate production
• Recruitment of fast glycolytic fibers

Question 27

What does the graph of blood lactate conc vs. exercise workload look like in relation to lactate threshold?

Answer 27

• Lactate conc is approximately constant until LT

- Above LT: lactate conc increases exponentially

Question 28

How does the body dispose of excess lactate?

Answer 28

Via shuttle mechanisms

Question 29

Describe intercellular (extra-muscular) lactate shuttle.

Answer 29

Use of lactate in other parts of the body (heart, liver, etc.)

Question 30

What is the intramuscular lactate shuttle?

Answer 30

Lactate is shuttled from low mitochondrial fiber to high mitochondrial fiber –> lactate converted to pyruvate –> undergoes anerobic metabolism

Question 31

What is the primary energy source during short duration intense exercise?

Answer 31

• CP
• Phosphagens
• ATP

Question 32

For what duration of maximal exertion is energy production roughly 50/50 anaerobic/aerobic?

Answer 32

1-2 mins

Question 33

How long does final steady state VO2 take to establish?

Answer 33

2-3 mins

Question 34

What is final steady state VO2 proportional to?

Answer 34

Total workload