Exercise physiology

Página 1

Substrates: Fuel for exercise

Terminology:

Metabolism: chemical reactions in the body

Anabolic reactions - synthesis of molecules

Catabolic reactions - break down of molecules

Substrates: fuel sources from which we make energy (adenosine triphosphate [ATP])

carbs, fat, protein

Bioenergetics: process of converting substrates into energy

performed at cellular level

the energy we derive from food is stored in cells in the form of ATP

ATP serves as the immediate source of energy for most body functions, including muscle contraction

Substrates

Carbs:

All carbohydrates converted to glucose

4.1 kcal/g; about 2,500 kcal stored in body

primary ATP substrate for muscles and brain

extra glucose stored as glycogen in liver and muscles

glycogen converted back to glucose when needed to make more ATP

Glycogen stores limited (2500 kcal) so we must rely on dietary carbohydrate to replenish stores

Fats:

provide a large portion of the energy utilized during prolonged, less intense exercise

efficient substrate, efficient stormge

9.4 kcal/g energy produced

70,000 kcal stored in body

energy substrate for prolonged, less intense exercise

high net ATP yield, but slow ATP production

must be broken down into free fatty acids (FFAs) and glycerol

only FFAs used to make ATP

Protein

energy substrate during starvation

produce 4.1 kcal/g of energy

must be converted into glucose

can also convert into FFAs

protein can supply up to 5-10% of energy during prolonged exercise

proteins must be broken down to their basic units-amino acids- to be used for energy

Controlling the Rate of Energy Production

rate primarily determined by the availability of the primary substrate and enzyme activity

the availability of large amounts of a substrate increases the activity of that particular pathway

Mass action effect:

substrate availability affects metabolic rate

more available substrate= higher pathway activity

excess of given substrate= cells rely on that energy substrate more than others

Enzymes: specific protein molecules that help control the rate of free-energy release.

speed up the breakdown (catabolism) of chemical compounds

speed up reaction by lowering the activation energy required to begin the reaction

more enzyme activity = more product

Phosphorylation: the addition of a phosphate group to ADP to generate ATP

ATP-PCr system

anaerobic (no oxygen required), substrate-level metabolism

ATP yield: 1 ATP/ 1 PCr

duration used: 3-15 seconds

because ATP stores in muscle are very limited, this pathway is used to reassemble and regenerate ATP

Phosphocreatine (PCr): ATP recycling

Pcr + creatine kinase = Cr + Pi + energy

PCr energy can't be used for cellular work

Pcr energy can be used to reassemble ATP

Replenishes ATP stores during rest

Recycles ATP during exercise until used up (3-15 sec. of maximal exercise)

Control of PCr system

Pcr breakdown catalyzed by creatine kinase (CK)

CK controls rate of ATP production through negative feedback

when ATP levels are down (ADP up), CK activity increases

when ATP levels are up, CK activity is down

Glycolytic System

anaerobic (doesn't require oxygen)

ATP yield: 2-3 ATP/ 1 mol substrate

Duration: 15sec.- 2 min.

Breakdown of glucose via glycolysis

Glycolytic System cont.

Uses glucose or glycogen as it's substrate

must convert to glucose-6-phosphate

costs 1 ATP for glucose, 0 ATP for glycogen

Pathway starts with glucose-6-phosphate, ends with pyruvic acid

10-12 enzymatic reactions total

all steps occur in cytoplasm

ATP yield: 2 ATP for glucose, 3 ATP for glycogen

Glycolysis: the breakdown of glucose through a pathway that involves a sequence of glycolytic enzymes

Adenosine triphosphate is generated through three energy systems:

The ATP-PCr system

The Glycolytic sustem

The oxidative system

In the ATP-PCr system, a phosphate group (Pi) is separated from PCr through the action of creatine kinase.

The Pi can then combine with ADP to for ATP using the energy released from the breakdown of PCr

this sustem is anaerobic and it's main function is to maintain ATP levels early in exercise

energy yield = 1 ATP/ 1 PCr

The glycolytic system involves the process of glycolysis, through which glucose or glycogen is broken down to pyruvic acid. When glycolysis occurs without oxygen, the pyruvic acid is converted to lactic acid. One molecule of glucose yields 2 ATP, but 1 mol. glycogen yields 3 ATP.

New Page