Exercise and Metabolism
How fit are you?
Rest to Exercise
•What changes must take place in skeletalmuscle at the beginning of exercise toprovide the necessary energy tocontinue movement?
•Increase demand for:
–O2
–ATP
During Exercise
•ATP consumption increases up to25 times than at rest
•ATP needed for muscle contractions
–ATP-PC system
–Glycolysis
–Aerobic pathway
O2 Deficit
•The lag in O2 uptake at the beginning ofexercise.
•This means initial ATP production mustbe anaerobic
The Oxygen Deficit
Trained vs. Untrained Subjects O2Deficit
•Trained athletes have lower oxygendeficit.
–aerobic ATP production begins sooner
•Due to:
–Better-developed aerobic capacity
–Cardiovascular or muscular adaptations
–Results in less production of lactic acid
»Lactic Acid = fatigue
Trained vs. Untrained
In Summary
In the transition from rest to light or moderate exercise,oxygen uptake increases rapidly, generally reaching asteady state within one to four minutes.
The term oxygen deficit applies to the lag in oxygenuptake in the beginning of exercise.
The failure of oxygen uptake to increase instantly at thebeginning of exercise suggests that anaerobic pathwayscontribute to the overall production on ATP early inexercise. After a steady state is reached, the body’s ATPrequirement is met via aerobic metabolism.
Recovery from Exercise
•Oxygen uptake remains elevated afterexercise and into recovery
•Metabolism remains elevated
–Increased body temp
O2 Debt
•Definition: the excess oxygenconsumption, above rest, followingexercise
•AV Hill
–“to repay the oxygen deficit that occurs atexercise onset”
O2 Debt
O2 Debt
•Divided into 2 portions:
•Rapid Portion
–2-3 minutes post exercise
•Slow Portion
–Greater than 30 minutes post exercise
Rapid Portion of O2 Debt
•First 20%
•Steep decline in O2 uptake followingexercise
•Due to:
–Resynthesis of creatine phosphate in muscle
–Replenishment of muscle and blood O2stores
Slow Portion
•80%
•Slow decline in O2 consumption afterexercise
•Due to:
–Elevated heart rate and breathing
• energy need
–Elevated body temperature
• metabolic rate
–Need to supply O2 to respiratory musclesfor breathing
Excess Post Exercise O2 Consumption
•EPOC / O2 Debt
Many scientists use these terms interchangeably
•EPOC is greater following higher intensityexercise
Oxygen Deficit and EPOCLight vs. Heavy Exercise
Factors Contributing to EPOC
O2 Consumption During Exercise
•Maximal oxygen consumption = VO2 max
•The maximal capacity to transport and useoxygen during exercise.
•Considered by many exercise scientists tobe the most valid measurement ofcardiovascular fitness.
Factors Influencing VO2 Max:
1.Ability of cardiorespiratory system todeliver oxygen to the muscle
2.Muscle’s ability produce ATP aerobically
3.Genetics
4.Exercise training
5.Cardiovascular Disease
6.Age
–VO2 max decreases with age
VO2 and Exercise Intensity
•Low intensity
–Fast walking
–30% VO2 max
•Moderate intensity
–Jogging
–50 – 80%
•High intensity
–Sprinting
–85 – 150%
Examples of VO2 max
•Healthy person
–20ml/kg/min
•Olympic Athlete
–>80ml/kg/min
•Heart Failure/ Transplant
–<14ml/kg/min
Lactate Threshold
•The point during exercise at which lacticacid starts to accumulate in the blood
•Lactic Acid is produced faster than it can beremoved
•Reflects the intensity of exercise
»Lactic Acid = fatigue
Training and Lactate Threshold
•LT can be increased with training.
–Trained athletes have a higher LT
•Interval training takes advantage of thebody being able to recover from LT.
–LA produced by the muscles is removed withoutit building up.
–Reduces fatigue
Training and Lactate Threshold
•A useful tool in training for racing andendurance sports
•Long distance activity: work just belowlactate threshold
–long distance running
–cycling, rowing
–swimming
–cross country skiing
Fuel Sources During Exercise
•Carbohydrates
–Blood sugar
–Glycogen
•Fats
–FFA
–Triglycerides
•How do you know what fuel you are using?
Respiratory Exchange Ratio
•RER
•Used to estimate fuel use during exercise
–Carbohydrate vs. Fat
–Done non invasively
–Metabolic Analysis
•Carbs and Fat utilize different amounts ofO2 and produce different amounts of CO2.
•Measure respiratory gasses during exercise.
C16H32O2 + 23 O2 16 CO2 + 16 H2O
VCO2
VO2
=
R =
16 CO2
23 O2
= 0.70
VCO2
VO2
R =
RER for Fats = 0.70
VCO2
VO2
=
R =
6 CO2
6 O2
= 1.00
C6H12O6 + 6 O2 6 CO2 + 6 H2O
RER for Carbs = 1.00
Respiratory Exchange Ratio
•CO2/ O2
•Fat oxidation requires more oxygen thancarbohydrate
•Carbohydrates contain more oxygen thanfat
R Value
•High R
–More carbohydrates
•Low R
–More fat
R value of .85
•.85
–50% comes from fat
–50% comes from carbohydrate
Estimation of Fuel Utilization During Exercise
Fuel Sources
•The source that is used is determined byexercise intensity
•Intense exercise utilizes carbs
•Low intensity exercise utilizes fats
Rate of Fat Metabolism at DifferentExercise Intensities
“Crossover” Concept
Is Low-Intensity Exercise Best forBurning Fat?
•At low exercise intensities (~20% VO2max)
–Fuel source is about 60% from fat
–However, total energy expended is low
•Total fat usage is also low
Is Low-Intensity Exercise Best forBurning Fat?
•At higher exercise intensities (~50% VO2max)
–Lower contribution of fat as fuel source
•(about 40%) from fat
–Total energy expended is higher
•Total fat usage is also higher
•“Fats burn in the flame of carbohydrates”
•Carbs are needed to introduce fats intothe cell.
•Glycogen stores can be depleted duringexercise.
Is Low-Intensity Exercise Best forBurning Fat?
Prolonged Exercise (over 2 hrs)
•May deplete muscle glycogen stores
•No products to send through the KrebsCycle
•No production of ATP
•Result: fatigue
end
Discussion Questions
•How can elite marathoners run 26.2 miles at apace of 5 minutes per mile, yet very few can runjust 1 mile in 4 minutes?
•Is it important for weight lifters and sprinters tohave a high capacity to consume oxygen?
•From an exercise perspective, what are someadvantages of having different sources ofpotential energy for synthesizing ATP
Influence of Exercise Intensity onMuscle Fuel Source
quiz
1.At rest ATP is produced by ….aerobic
2.Tf factors contributing to o2 debt includeresynthesis or creatine phosphate and bodytemp. t
3.The upward drift in o2 uptake duringexercise is due to ….increasing bodytemperature
4.Tf maximal o2 uptake provides and overallassesment of exercise capability and isreduced in patients with cardio pulmonarydisease. T
Crossover happens because…
1.Fast muscle fibers prefer glycolysis
2.Increasing levels of epinephrine
•The rise in epinephrine increases muscleglycogen breakdown
•Increased lactate production inhibits fatmetabolism
Factors Governing Fuel Selection
Sources of CarbohydrateDuring Exercise
•Blood glucose
–From liver (glycogen to glucose)
–Primary source during low-intensity exercise
–Important during long-duration exercise
•As muscle glycogen levels decline
•Muscle glycogen
–Primary source during high-intensity exercise
–Supplies much of the carbohydrate in the first hourof exercise
Factors Governing Fuel Selection
Sources of Fat During Exercise
•Muscle stores of Triglycerides
–Primary source of fat during higher intensityexercise
•Plasma FFA
–From adipose tissue
–Enters Krebs cycle
–Source of fat during low-intensity exercise
–Becomes more important as muscletriglyceride levels decline in long-durationexercise
Work rate can still increase, eventhough there is no increase in O2consumption
Calculate VO2 max
•VO2 max = cardiac output X arterial/venusoxygen difference at peak exercise
•Cardiac output- the amount bloodpumped by the heart
•Arterio venus oxygen difference – thedifference in oxygen between the arteriesand veins.
Lactate Threshold & Stats
•Blood samples taken during exercise
•Untrained person achieves threshold at 40-60% VO2 max
•Trained person
–Threshold at 65-80%VO2 max
•Elite athletes
–80-90 % of VO2 max
In Summary
Oxygen uptake increases in a linear fashionduring incremental exercise until VO2 max isreached.
The point at which blood lactic acid risessystematically during graded exercise istermed the lactate threshold or anaerobicthreshold.
The lactate threshold has practical uses suchas in performance prediction and as amarker of training intensity.
Factors Governing Fuel Selection
Shift From Carbohydrate to FatMetabolism During ProlongedExercise
Figure 4.13
