55C H A P T E R

Bioenergetics of Exercise and TrainingBioenergetics of Exercise and Training

Mike Conley

Chapter Outline

Essential terminology

Biological energy systems

Substrate depletion and repletion

Bioenergetic limiting factors in exercise performance

Oxygen uptake and the aerobic and anaerobic contributions to exercise

Metabolic specificity of training

Essential Terminology

Energy

Bioenergetics

Catabolism

Anabolism

Exergonic reactions

Metabolism

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

Adenosine monophosphate (AMP)Endergonic reactions

Chemical Structures of ATP, ADP, and AMPChemical Structures of ATP, ADP, and AMP

Energy stored in the chemical bonds of

adenosine triphosphate (ATP) is used to power

muscular activity. The replenishment of ATP in

human skeletal muscle is accomplished by

three basic energy systems: phosphagen,

glycolytic, and oxidative.

Phosphagen (Anaerobic) System

Occurs in the absence of molecular oxygen

Provides ATP for short-term, high-intensity activities

Is active in the start of all exercise regardless of intensity

Myosin ATPase and Creatine Kinase ReactionsMyosin ATPase and Creatine Kinase Reactions

Myokinase ReactionMyokinase Reaction

Glycolytic System

Breaks down carbohydrates to produce ATP that supplements the supply from the phosphagen system for high-intensity muscular activity

May go in one of two ways: fast glycolysis and slow glycolysis

During fast glycolysis, pyruvate is converted

to lactic acid, providing ATP at a fast rate

compared with slow glycolysis, in which

pyruvate is transported to the mitochondria for

use in the oxidative system.

Fast glycolysis has commonly been called

anaerobic glycolysis, and slow glycolysis,

aerobic glycolysis, as a result of the ultimate

fate of the pyruvate. However, because

glycolysis itself does not depend on oxygen,

these terms are not practical for describing the

process.

GlycolysisGlycolysis

The Cori CycleThe Cori Cycle

Lactate Threshold (LT) and Onset of Blood Lactate Accumulation (OBLA)Lactate Threshold (LT) and Onset of Blood Lactate Accumulation (OBLA)

Oxidative (Aerobic) System

Requires molecular oxygen

Uses primarily carbohydrates and fats as substrates

Provides ATP at rest and during low-intensity activities

The oxidative metabolism of blood glucose

and muscle glycogen begins with glycolysis. If

oxygen is present in sufficient quantities the

end product of glycolysis, pyruvate, is not

converted to lactic acid but is transported to the

mitochondria, where it is taken up and enters

the Krebs Cycle, or citric acid cycle.

Krebs CycleKrebs Cycle

Electron Transport ChainElectron Transport Chain

Metabolism of Fat, Carbohydrate, and ProteinMetabolism of Fat, Carbohydrate, and Protein

In general, an inverse relationship exists

between the relative rate and total amount of

ATP that a given energy system can produce.

As a result, the phosphagen energy system

primarily supplies ATP for high-intensity

activities of short duration, the glycolytic

system for moderate- to high-intensity activities

of short to medium duration, and the oxidative

system for low-intensity activities of long

duration.

Table 5.3 Effect of Event Duration on Primary Energy System Used

Duration Intensity Primary energyof event of event system(s)

0-6 s Very intense Phosphagen

6-30 s Intense Phosphagen and fastglycolysis

30 s-2 min Heavy Fast glycolysis

2-3 min Moderate Fast glycolysis andoxidative system

> 3 min Light Oxidative system

Table 5.4 Rankings of Rate and Capacity of ATP Production

System Rate of ATP Capacity of ATPproduction production

Phosphagen 1 5

Fast glycolysis 2 4

Slow glycolysis 3 3

Oxidation of carbohydrates 4 2

Oxidation of fats and proteins 5 1

1 = fastest/greatest; 5 = slowest/least

The extent to which each of the three energy

systems contributes to ATP production depends

primarily on the intensity of muscular activity

and secondarily on the duration. At no time,

during either exercise or rest, does any single

energy system provide the complete supply of

energy.

Low-Intensity, Steady-State Exercise MetabolismLow-Intensity, Steady-State Exercise Metabolism

EPOC = Excess postexercise oxygen uptake

High-Intensity, Non-Steady-State Exercise MetabolismHigh-Intensity, Non-Steady-State Exercise Metabolism

The use of appropriate exercise intensities

and rest intervals allows for the “selection” of

specific energy systems during training and

results in more efficient and productive

regimens for specific athletic events with

various metabolic demands.