16. Metabolism During Exercise Flashcards
What is TEA? What % of daily energy needs does this comprise? How variable is it?
- Thermic Effect of Activity
- 15-50% of daily energy needs
- Largest potential variable, day to day
What is EPOC? What % of daily energy needs does it comprise?
- Excess postexercise oxygen consumption
- Recovery O2 consumption in excess of resting O2 consumption
- Less than 1% of daily energy needs
What is TEF? What % of daily energy needs does it comprise?
- Thermic Energy of Feeding
- “It takes calories to absorb calories”
- 10% of daily energy need
Direct vs. Indirect Calorimetry. What does each measure? How different are they from each other?
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
What is calorimetry?
Measurement of energy expenditure
What does heat of combustion refer to? What does it represent?
- Refers to heat liberated by oxidizing a specific food
- Represents the food’s total energy value
What is the heat of combustion for 1 g of CHOs? Lipids? Proteins?
- CHOs = 4.2 kcal
- Lipids = 9.4 kcal
- Proteins = 5.65 kcal
How is the rate of oxygen uptake (VO2) obtained during indirect calorimetry?
From measurements of expired ventilation and fractions of expired O2 and CO2, assuming no change in body stores of O2, CO2, and N2
What is RQ? What does it reflect?
- Respiratory Quotient
- # of moles of CO2 produced per mole of O2 consumed
- Reflects oxidative metabolism at the cellular level
What is RER? What does it measure?
- Respiratory Exchange Ratio
- Measures rates of O2 consumed and CO2 produced using expired air measured at mouth
What is the relation between RQ and RER?
RQ = RER under steady state conditions
Metabolic responses to work onset are a consequence of:
- Rate limits of each metabolic pathway
- Recruitment patterns of motor units
When does oxygen uptake occur relative to the onset of work?
Oxygen uptake follows the onset of work
What is oxygen deficit? When does it occur?
- 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
What is does steady state look like on a graph? What does it reflect?
- The plateau
- Reflects a balance between energy required by the working muscle and the ATP production in aerobic metabolism
What fuels the O2 deficit?
- Phosphagens
- Anaerobic glycolysis
- O2 stored in hemoglobin & myoglobin
What does the magnitude of the O2 deficit depend on?
- Intensity of exercise
- State of training
- Dieting
- Warmup
How does the size and rate of EPOC vary in light, moderate, and hard exercise?
Increases in size and rate w/ increased intensity of exercise
What are some reasons why oxygen consumption may be elevated following exercise?
LOOKUP
What substrates are being metabolized or regenerated following exercise?
LOOKUP
What is maximal oxygen consumption (VO2 max)?
- Measure of aerobic capacity for fitness
- Max amount of O2 that an individual can utilize during intense exercise
If a person doesn’t reach a physiologic plateau in their VO2 before fatigue, their highest VO2 is called what?
Peak VO2 = symptom-limited VO2max
What is the criteria for VO2max?
- RER >/= 1.1
- [lactate] > 8 mmol/L
- HR approx. 220-age
- RPE >/= 15 (very hard)
What type of athletic performance does VO2max predict?
Aerobic capacity for fitness
What is lactate threshold? Where is this point on a blood lactate vs. exercise workload graph?
- Point at which lactate entry into blood exceeds its removal
- On graph: inflection upward on exponential increase
List 4 potential factors that lead to the exponential increase in lactate accumulation at high workload.
- Low muscle oxygen tension
- Accelerated glycolysis (increase in pyruvate conc)
- Reduced rate of lactate removal relative to lactate production
- Recruitment of fast glycolytic fibers
What does the graph of blood lactate conc vs. exercise workload look like in relation to lactate threshold?
- Lactate conc is approximately constant until LT
- Above LT: lactate conc increases exponentially
How does the body dispose of excess lactate?
Via shuttle mechanisms
Describe intercellular (extra-muscular) lactate shuttle.
Use of lactate in other parts of the body (heart, liver, etc.)
What is the intramuscular lactate shuttle?
Lactate is shuttled from low mitochondrial fiber to high mitochondrial fiber –> lactate converted to pyruvate –> undergoes anerobic metabolism
What is the primary energy source during short duration intense exercise?
- CP
- Phosphagens
- ATP
For what duration of maximal exertion is energy production roughly 50/50 anaerobic/aerobic?
1-2 mins
How long does final steady state VO2 take to establish?
2-3 mins
What is final steady state VO2 proportional to?
Total workload
