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Exercise Physiology Chap 4

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Measurement of oxygen consumption (VO2)
1. VO2 - Ability to Deliver & Use Oxygen

2. Expressed 2 ways-
- Liters per minute (L/min) (Absolute VO2)
- ml per kg of body weight per minute (ml/kg/min)(Relative VO2)
Energy Requirements at Rest
1.) Almost 100% of ATP produced by aerobic metabolism

2.) Blood lactate levels are low (<1.0 mmol/L)

3.) Resting O2 consumption (70 kg adult):
- 0.25 L/min (absolute VO2)
- 3.5 ml/kg/min (relative VO2)
Metabolic Equivalents (MET)
The expression of energy cost for activities in a simple unit.

For the masses much like BMI.

Energy cost of exercise can be expressed in MET.

It is equal to 3.5 ml/kg/min VO2 at resting level
- 1 MET = 3.5 ml/kg/min
Measuring VO2max
VO2max - maximal rate to transport and use oxygen.

A maximal oxygen consumption (VO2max) test requires that the participant use maximal effort in performing physical work to exhaustion by using bike or treadmill.

The test begins with a light workload and progresses, with increases every 2-3 minutes, to a workload that the participant can no longer sustain.

Oxygen uptake increases linearly until VO2max is reached
No further increase in VO2 with increasing work rate

Considered by many to be most valid measurement of cardiovascular fitness
Measuring VO2max
The most relevant criteria are:

1. the plateau of oxygen consumption

2. the attainment of respiratory exchange ratios (RER = CO2/O2) of 1:1 or
higher.

3. the attainment of age-predicted HR

4. the exhaustion of the participant

5. blood [La] > 8.0 mM/L
Rest-to-Exercise Transitions
1. ATP production increases immediately
2. Oxygen uptake increases rapidly
-Reaches steady state within 1-4 minutes
-After steady state is reached, ATP requirement is met through aerobic ATP production
3. Initial ATP production through anaerobic pathways
-ATP-PCr system
-Fast Glycolysis
4. Oxygen deficit
-Delay in oxygen uptake at the beginning of exercise
The Oxygen Deficit
Lag in oxygen consumption
at the onset of exercise
- Oxygen deficit

ATP production at the onset of
exercise is maintained by:
- oxygen stores (O2 bound to
myoglobin)
- ATP-PC
- fast glycolysis
What is the difference in VO2 Between Trained and Untrained Subjects?
The difference is the trained subjects have a better developed aerobic bioenergetic capacity, resulting from either cardiovascular or muscular adaptations induced by endurance training.
Inadequate oxygen delivery means
Delayed steady state in VO2 (increase in oxygen debt)
Oxygen Deficit
Oxygen Deficit:
the difference between the total oxygen actually consumed during exercise and the total oxygen required (consumed) in steady-rate from the start of exercise.

As begin exercise, not producing enough O2 to do work.

Then, the body borrows on its energy reserves (credits). After exercise, the body tries to pay back those credits plus some interest.
Summary for O2 Deficit
As begin exercise, not producing enough O2 to do work:
(1) Accumulate Lactate
(2) This is the O2 deficit
(3) This will have to be paid back (metabolized later
Comparison of Trained and Untrained Subjects
1.) Trained subjects have a lower oxygen deficit
- Better-developed aerobic bioenergetic capacity
- Due to cardiovascular or muscular adaptations
2.) Results in less production of lactic acid
Excess Postexercise Oxygen Consumption (EPOC
After exercise, O2 consumption does not return to resting levels immediately.

Then, the extra O2 consumed during recovery, above a resting baseline is called Excess Postexercise Oxygen Consumption (EPOC).

EPOC is also termed O2 debt.
Excess Post-Exercise Oxygen Consumption (EPOC)
1.) Oxygen consumption remains elevated following exercise
- Classical term - oxygen debt

- Depends on intensity and duration of activity

- Rapid curve component ("Rapid" portion ) - steep decline

- Slow curve component ("Slow" portion)
Oxygen Debt (EPOC)
1.) Rapid curve component
- Steep decline in O2 consumption
- Replenish ATP, PC, Oxygen stores.

2.) Slow curve component
- Slow decline in O2 consumption
- Elevated heart rate and breathing = energy need
- Elevated body temperature = metabolic rate
- Elevated epinephrine and norepinephrine = metabolic rate
- Conversion of lactic acid to glucose (gluconeogenesis)
EPOC is Greater Following Higher Intensity Exercise
1.) Higher body temperature
2.) Greater depletion of PC
3.) Greater blood concentrations of lactic acid
4.) Higher levels of blood epinephrine and norepinephrine
EPOC
During recovery, 4/5 of the lactate is oxidized and 1/5 is reconverted to glycogen.

Because blood lactate does not decline immediately (a delay), Fast Curve of EPOC is NOT associated with a change in blood lactate (nothing to do with lactate metabolism).

Slow Curve of EPOC coincides with the decline in blood lactate that is due to the reconverted of lactate to glycogen.
Metabolic Responses to Prolonged Exercise
1.) Prolonged exercise (>10 minutes)
- ATP production primarily from aerobic metabolism
- Steady-state oxygen uptake can generally be maintained during submaximal exercise
2.) Prolonged exercise in a hot/humid environment or at high intensity
- Upward drift in oxygen uptake over time
- Due to body temperature and rising epinephrine and norepinephrine
Lactate Threshold
1.) The point at which blood lactic acid rises systematically during incremental exercise
- Appears at ~50-60% VO2 max in untrained subjects
- At higher work rates (65-80% VO2 max) in trained subjects
2.) Also called:
- Anaerobic threshold
- Onset of blood lactate accumulation (OBLA)
- Blood lactate levels reach 4 mmol/L
Explanations for the Lactate Threshold
1.) Low muscle oxygen (hypoxia)
2.) Accelerated glycolysis
- NADH produced faster than it is shuttled into mitochondria
- Excess NADH in cytoplasm converts pyruvic acid to lactic acid
3.) Recruitment of fast-twitch muscle fibers
- LDH isozyme in fast fibers promotes lactic acid formation
4.) Reduced rate of lactate removal from the blood
Factors affecting lactate appearance and disappearance
1.) [La] = rate of appearance - rate of disappearance
- What affects appearance?
- Production and release
- Recruitment of fast twitch fibers
- LDH isoform
- Increased epinephrine
- What affects disappearance?
- Rate of uptake into non-working muscles
- Oxidation by muscles, liver
- Blood flow
Lactate threshold as a percentage of VO2max
Allowing greatest work rate without rapid increase in blood lactate concentration in Trained individuals
Practical Uses of the Lactate Threshold
1.) Prediction of performance
- Combined with VO2 max
2.) Planning training programs
Marker of training intensity
Removal of Lactate
70% - oxidized by other tissues

20% - converted to glycogen or glucose in liver (Cori Cycle)

10% - converted to amino acids
RER (respiratory exchange ratio)
1.) RER-respiratory exchange ratio
- an estimate of the primary substrate (food) being used to make ATP.
- RER (R) = CO2 produced / O2 taken in
- Measured at the mouth

2.) CHO and FAT are primary fuels and are burned with O2, and CO2 is the waste product

3.) During steady-state exercise
- VCO2 and VO2 reflective of O2 consumption and CO2 production at the cellular level
RER (respiratory exchange ratio)
1.) RER at rest ranges from 0.75 to 0.85.
2.) Because RER depends on the type of the fuel used by the cells, it can help provide an index of carbohydrate or fat metabolism.

Fat = C16H32O2
C16H32O2 + 23O2 16CO2 + 16H2O
RER = VCO2/VO2 = 16 CO2 / 23O2 = 0.70 (RER)

Glucose = C6H12O6
C6H12O6 + 6O2 6CO2 + 6H2O
RER = VCO2/VO2 = 6 CO2 / 6O2 = 1.00 (RER)
RER (respiratory exchange ratio)
At high levels of exercise (maximal exercise), CO2 production exceeds Oxygen Uptake, and an RER will exceed 1.0 to 1.2 that is often used to indicate that the subject is giving a maximal effort.
Respiratory Exchange Ratio (R or RER)
1.) RER (R) = CO2 produced / O2 taken in
- Measured at the mouth

2.) RER (R) can exceed 1.0
- Bicarbonate buffering
- Non-metabolic CO2 production

H+ + HCO3- <--> H2CO3 <-->H2O + CO2
Inadequate oxygen deliver
anaerobic metabolism (increase in lactic acid)
Protein Metabolism during Prolonged Exercise
Proteases - break down protein / increase with long term exercise

May contribute to as much as 5 to 10% of energy production during prolonged exercise.
Utility of R value
1.)Indication of respiratory substrate
2.)Estimation of kcals expended
- Add 4.0 to R value to estimate kcals expended per liter of oxygen consumed
- R = .85
- 4.85 kcals/liter O2
Calories from R Value
Calories (kcals)- we are able to estimate the caloric cost of exercise from the R value (CO2/O2) measured in human breath.

Calculating caloric cost of exercise bout can only be done if a steady state VO2 is achieved.
Calories from RER
1.) Calculate calories from RER
- Add 4 to steady state RER value obtained off the metabolic cart.

- Ex. RER= .80 + 4 = 4.80 kcals per liter of O2 consumed.

2.) Multiply the kcals by the absolute VO2 of total exercise duration

Ex. 2.5 L/min for 10 min = 25L of 02 used during exercise.

3.) RER= .80 and you consumed 25 Liters of O2
- 4.80 kcals/L X 25 LO2= 120 kcals burned in 10 mins
Exercise Intensity and Fuel Selection
1.) Low-intensity exercise (<30% VO2 max)
- Fats are primary fuel
2.) High-intensity exercise (>70% VO2 max)
- Carbohydrates are primary fuel
3.) "Crossover" concept
- Describes the shift from fat to CHO metabolism as exercise intensity increases
- Due to:
- Recruitment of fast muscle fibers - ↑ glycolytic enzymes; few mitochondria and few lipolytic enzymes to break down fat.
- Increasing blood levels of epinephrine - increase muscle glycogen breakdown
Is Low-Intensity Exercise Best for Burning Fat?
1). At low exercise intensities (~20% VO2 max)
- High percentage of energy expenditure (~60%) derived from fat
- However, total energy expended is low
-Total fat oxidation is also low
2.) At higher exercise intensities (~50% VO2 max)
- Lower percentage of energy (~40%) from fat
- Total energy expended is higher
- Total fat oxidation is also higher
Exercise Duration and Fuel Selection
1.) Prolonged, low-intensity exercise
- Shift from carbohydrate metabolism toward fat metabolism
2.) Due to an increased rate of lipolysis
- Breakdown of triglycerides glycerol + FFA
- By enzymes called lipases
- These lipases are stimulated by rising blood levels of epinephrine and norepinephrine
Carbohydrate Feeding via Sports Drinks Improves Endurance Performance
1.) The depletion of muscle and blood carbohydrate stores contributes to fatigue
2.) Ingestion of carbohydrates can improve endurance performance
- During submaximal (<70% VO2 max), long-duration (>90 minutes) exercise
- 30-60 g of carbohydrate per hour are required
Sources of Carbohydrate During Exercise
1.) Muscle glycogen
- Primary source of carbohydrate during high-intensity exercise
- Supplies much of the carbohydrate in the first hour of exercise
2.) Blood glucose
- From liver glycogenolysis
- Primary source of carbohydrate during low-intensity exercise
- Important during long-duration exercise
-As muscle glycogen levels decline
Sources of Fat During Exercise
1.) Intramuscular triglycerides
- Primary source of fat during higher intensity exercise
2.) Plasma FFA
- From adipose tissue lipolysis
Triglycerides -> glycerol + FFA
- FFA converted to acetyl-CoA and enters Krebs cycle
- Primary source of fat during low-intensity exercise
- Becomes more important as muscle triglyceride levels decline in long-duration exercise
Sources of Protein During Exercise
1.) Proteins broken down into amino acids
- Muscle can directly metabolize branch chain amino acids and alanine
- Liver can convert alanine to glucose
2.) Only a small contribution (~2%) to total energy production during exercise
- May increase to 5-10% late in prolonged-duration exercise
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