Chapter 4Exercise Metabolism and

Bioenergetics

Objectives

• After this presentation, the participant will be able to: – Describe the primary methods of how the body produces energy for

exercise.

– Differentiate between and define aerobic and anaerobic metabolism.

– Distinguish which energy pathways are used for various intensities and durations of exercise.

– Understand the interaction of carbohydrate, fat, and protein as fuels for exercise.

– State the differences in the energy use during steady state and exhaustive exercise.

– Describe basic training-induced adaptations in energy production.

Bioenergetics

• Bioenergetics is the study of how energy is transformed through various biochemical reactions– Metabolism refers to all the chemical reactions that

occur in the body to maintain itself – Exercise metabolism refers to the examination of

bioenergetics as it relates to the unique physiologic changes and demands placed on the body during exercise

Nutrient Substrates

• Proteins, carbohydrates, and lipids (fats) constitute the main substrates used to transfer metabolic energy to be used for all types of cellular activity and life

• Carbohydrates provide the body with a source of fuel and energy required for all daily activities including exercise. – The storage form of carbohydrates, called

glycogen

Nutrient Substrates

• Another important source of energy is fat. The chemical or substrate form in which most fat exists in food as well as in the body is called triglycerides. Fat is mainly used as fuel during low intensity, long duration exercise.

• The third fuel source is protein. But protein rarely supplies much energy during exercise. During a low calorie diet, protein can be used as fuel to supply carbohydrates via gluconeogenesis. This is why muscle loss typically happens when using the low calorie method of dieting.

• Gluconeogenesis: The formation of glucose from noncarbohydrate sources, such as amino acids.

Energy and Work

• Adenosine Triphosphate is one of the primary sources of immediate energy for cellular metabolism stored in chemical bonds– When the chemical bonds that hold ATP together are

broken, energy is released and utilized for cellular work. This leaves behind another molecule called adenosine diphosphate (ADP)

– To perform mechanical work ATP is required

Energy and Work

• ATP-PC system- Provides energy for short duration high intensity work,* by replenishing ATP rapidly (6-10 seconds)

• Glycolysis- Provides energy through the breakdown of glucose to create ATP for moderate intensity, moderate duration work (30-50 seconds)

• Oxidative system-The most complex of the three energy systems is the process that uses substrates with the aid of oxygen to generate ATP.

The Oxidative System

• The three oxidative or aerobic systems include:– 1. Aerobic glycolysis– 2. The Krebs cycle– 3. The electron transport chain (ETC)– Fat can also be metabolized aerobically. Fat is the

preferred fuel source for aerobic activities of long duration like a marathon.*

– The first step in the oxidation of fat is a process referred to as β-oxidation

• Produces lots of ATP, but very slowly

Energy During Exercise

• Intensity and duration of exercise are inversely related. – The amount of energy available from stored

ATP and phosphocreatine is small, whereas the amount of energy from stored carbohydrate has a greater capacity, but is still limited

– The amount of available fuel for exercise from fats is essentially unlimited.

Energy During Exercise

• Costs of exercise vary depending on conditions– Lying supine burns fewer calories than standing

exercise– The body prefers oxidative metabolism– Excess postexercise oxygen consumption-

Elevated oxygen consumption after strenuous exercise

– During intermittent work glycolysis provides energy for work, oxidative provides recovery

Fuel Contribution During Exercise

• The bioenergetics of exercise can be indirectly measured in a laboratory using various modes of exercise by measuring the respiratory quotient.

• The respiratory quotient (RQ) is the amount of carbon dioxide (CO2) expired divided by the amount of oxygen (O2) consumed, measured during rest or at steady state of exercise using a metabolic analyzer

– An RQ of 1.0 indicates that carbohydrate is supplying 100% of the fuel

– An RQ of 0.7 indicates that fat is supplying 100% of the fuel. – An RQ between 0.7 and 1.0 indicates a mixture.

Summary

• Bioenergetics is the study of how energy is transformed through various biochemical reactions

• Metabolism refers to all the chemical reactions that occur in the body to maintain itself

• Proteins, carbohydrates, and lipids (fats) constitute the main substrates used

• ATP is the chemical form of energy derived from three pathways

• RQ determines percentage of fat, carbs, or protein utilized in exercise