Fuel for Exercise 2

Oxidation of fat: Triglycerides

broken down into 1 glycerol + 3 FFAs

lipolysis, carried out by lipases

Oxidation of Fat: Rate of FFA entry into muscle

dependent on centration gradient

Oxidation of fat: Yield

3 to 4 times more ATP than glucose

Oxidation of Fat: ATP production is slower than

glucose oxidation

Beta Oxidation (β) of fat: process

converting FFAs to acetyl-CoA before entering Krebs Cycle (invest)

Beta Oxidation (β) of Fat: upfront expenditure of

2 ATP

Beta Oxidation (β) of Fat: Number of steps dependent on

number of carbons on FFA

Oxidation of Protein:

Rarely used as a substrate (starvation)

Oxidation of protein can be converted to

glucose

Gluconeogenesis

converting protein to glucose

After gluconeogenesis, it can be converted into

acetyl-CoA

Oxidation of Protein: Energy Yield

Nitrogen presence is unique

Nitrogen excretion requires ATP expenditure

Lactate use of muscles

it is produced in cytoplasm can be taken up by mitochondria of the same muscle fiber and oxidized

Muscles using lactate

it can be transported via monocarboxylate transporters to another cell and oxidized there (lactate shuffle)

Muscles using lactate in another way

it can recirculate back to the liver and be reconverted to pyruvate and then to glucose through gluconeogenesis

Interaction of energy systems: all three systems interacting for all activites

no single system contributes 100% (varies)

one system often dominates for a given task

cooperation increases during transition periods

Crossover Concept: At rest and exercise below 60% VO2max

lipids serve as the primary substrate

Crossover Concept: during high intensity (above 75% VO2max)

carbohydrates serve as the primary substrate

Crossover point

intersection which is affected by exercise intensity and endurance training

Oxidative capacity of muscle

not all muscles exhibit maximal oxidative capabilities

Factors determining oxidative capacity

enzyme activity

fiber type composition, endurance training

O2 availability versus O2 need

Fiber Type Composition and Endurance Training: Type 1 fibers

greater oxidative capacity, more mitochondria, high oxidative enzyme concentrations, more cappilaries

Type II muscle fibers are better equipped for

glycolytic energy production

Fiber Type Composition: Endurance Training

enhances oxidative capacity of type II fibers

develops more (and larger) mitochondria

Develops more oxidative enzymes per mitochondrion

increases capillary number

Enzyme Activity

not all muscles exhibit optimal activity of oxidative enzymes

Enzyme activity predicts

oxidative potential

Representative enzymes

succinate dehydrogenase (SHD)

citrate synthase (CS)