Chapter 4
Exercise Metabolism
Part 2

EXERCISE PHYSIOLOGY

Lactate Threshold
Sometimes defined as the ___________________, or the Onset of ____________ ______________ Accumulation (OBLA)

•Defined as: The point at which blood lactic acid suddenly ____________ during incremental exercise

Mechanisms for lactate threshold

–__________ muscle oxygen

–Accelerated ________________

–Recruitment of ______________ muscle fibers

–Reduced rate of ______________ _____________ from the blood

Practical uses in prediction of performance and as a marker of exercise intensity

Question?

Identification of the
Lactate Threshold

Mechanisms to Explain the Lactate Threshold

Mechanisms for OBLA
at the mitochondria level

LA ______________ in glycolysis when the shuttle system in the ________________ cannot keep up with the rate of _______________ production in glycolysis.

_______________ acid therefore accepts some of the unshuttled H+ ions and __________ is formed, irregardless of the level of O2 in the working muscle.

Other Mechanisms for the Lactate Threshold

Controversy Exists In Any One Line of Thinking Over the Other

Failure of the mitochondrial hydrogen shuttle to keep pace with glycolysis

–Excess ________________ in sarcoplasm favors conversion of _____________ acid to ___________ acid

Type of ____________ (Lactate Dehydrogenase Enzyme)

–LDH is an enzyme that converts pyruvic acid to lactic acid

–LDH in _______________ fibers favors formation of _______ acid (LDH formed in fast-twitch has an affinity to attach to _________________, promoting ________ Acid.)

Effect of Hydrogen Shuttle and LDH on Lactate Threshold

Why does muscle soreness exist 24 - 48 hours after exercise?

Estimation of Fuel Utilization During Exercise

•Respiratory exchange ratio (RER or R)

–___________ / ___________ (Measured in ___________ State Only)

•R is a “__________________” way of estimating the percent of fuels (food substrates) being utilized for energy metabolism.

Fat (palmitic acid) = C₁₆H₃₂O₂

C₁₆H₃₂O₂ + 23O₂ ® 16CO₂ + 16H₂O + ?ATP

R = VCO₂/VO₂ = 16 CO₂ / 23O₂ = 0.70

(R = ____________ indicates that energy is being derived almost 100% from fats)

Glucose = C₆H₁₂O₆

C₆H₁₂O₆ + 6O₂ ® 6CO₂ + 6H₂O + ?ATP

R = VCO₂/VO₂ = 6 CO₂ / 6O₂ = 1.00

(R = __________ indicates that energy is being derived almost 100% from CHO)

Generalizations on the Utilization of Fuels During Exercise
R ratio

The R ratio indicates that ___________________ requires more Oxygen than does Carbohydrate to oxidize.

CHO has more _____________ than fat does.

Question

Is Protein used for fuel at a higher rate during prolonged exercise?

Answer: _________

Protein is used ___________ ____ % during exercise lasting less than 1 hour (< 1 hr.) and 3-5 times ____________ during prolonged exercise > 3 hours.

Estimation of Fuel Utilization During Exercise

•Indications of fuel utilization (expressed in R)

•0.70 = 100% fat

•0.85 = _________ fat, _________ CHO

•1.00 = 100% CHO

Taken: During _____________-state exercise

–VCO₂ and VO₂ reflective of O₂ consumption and CO₂ production at the cellular level

Exercise Intensity and Fuel Selection

•Low-intensity exercise (<30% VO_2max)

–______________ are primary fuel

•High-intensity exercise (>70% VO_2max)

–_______________ are primary fuel

•“_________________” concept

–Describes the shift from ___________ to ____________ metabolism as exercise intensity increases

Due to:

•Recruitment of ____________ muscle fibers

•Increasing blood levels of _________________

Illustration of the
“Crossover” Concept

Exercise Duration and Fuel Selection

•During prolonged exercise, there is a shift from _____________ metabolism toward ___________ metabolism

Increased rate of lipolysis

–Breakdown of triglycerides into __________ and __________ ___________ acids (FFA)

–Stimulated by ______________ blood levels of _______________

Shift From CHO to Fat Metabolism During Prolonged Exercise

Breakdown of ______________ to ______________

Interaction of Fat and CHO Metabolism During Exercise

•“Fats burn in a ____________________ flame”

•Glycogen is ________________ during prolonged high-intensity exercise

–_______________ rate of glycolysis and production of pyruvate

–_______________ Krebs cycle intermediates

–_______________ fat oxidation

•_________________ are metabolized by Krebs cycle

Lypolysis Defined

•Triglycerides --------> _________________ Acids & ___________ in the presence of ______________ (enzyme)

•Lipases enzymes are stimulated by hormones _______________, norepinephrine and glycagon.

•This is a _____________ PROCESS

•Fat metabolism occurs only after ___________ _____________ of exercise (See Fig. 4.14)

•Lactic Acid and Insulin ____________ Lypolysis

What Controls The Rate of Fat Metabolism During Prolonged Exercise (Fat Metabolism is called Lipolysis)?

•1. During low-intensity, prolonged exercise, blood levels of epinephrine ______________, which ____________ lipase activity, thereby promoting_______________ lipolysis

Yielding

•2. An increase in blood __________ _________ acids (FFA) and an increase in __________ metabolism.

•So, ____________ and _________________ enzymes control the rate of fat metabolism during prolonged exercise.

Insulin and Lypolysis

•Insulin inhibits _________________ by directly inhibiting lipase activity (the enzyme that converts triglycerides to FFA).

•So, if a high sugar drink consumed, prior to competition or exercise, what would this do to blood glucose levels?

•High blood sugar (glucose) causes the pancreas to __________________ insulin to sweep the _____________ into the fat cell. At the same time, the insulin ________________ the lipase enzyme from breaking down ______________ to FFA, needed for fuel and energy.

Sources of Fuel During Exercise

•Carbohydrate

–Blood _______________

–Muscle ________________

•Fat

–Plasma _______________________ (from adipose tissue lipolysis)

–Intramuscular triglycerides

•Protein

–Only a small contribution to total energy production (only ~__________)

•May increase to _________ __________ late in prolonged exercise

•Blood lactate

–Gluconeogenesis via the Cori cycle

Effect of Exercise Intensity on Muscle Fuel Source

Effect of Exercise Duration on Muscle Fuel Source

Where is Glycogen Stored?

The Cori Cycle:
Lactate As a Fuel Source

Application of the Cori Cycle