Fitness Foundations

Module 17: Exercise Metabolism and Bioenergetics

INTRODUCTION TO EXERCISE METABOLISM AND BIOENERGETICS

Bioenergetics and Metabolism

• Bioenergetics―the study of how energy is transformed through biochemical reactions in the human body

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

Bioenergetics and Metabolism

• Exercise Metabolism― the examination of bioenergetics relating to the unique physiologic changes and demands place on the body during exercise.

Supply of Energy

• Exercise places demanding requirements to supply energy and remove metabolic by-products

• Food we eat provides energy, but has to be converted into units called substrates:– Carbohydrates– Proteins– Fats

Supply of Energy

The energy in the substrate molecules is chemically released in cells and stored in a high-energy compound called ATP

Fuel for Energy Metabolism

Food provides energy to sustain life and support physical activity, but first has to be broken down by the digestive system into substrates.

Carbohydrates

• Provide body with fuel and energy for all daily activities including exercise

• Lack of carbohydrates in diet can cause:– Fatigue– Poor mental function– Lack of endurance and

stamina

Composition of Carbohydrates

• Organic compounds of carbon, hydrogen, and oxygen, which include starches, cellulose, and sugars

• Important source of energy• All carbohydrates are

eventually broken down in the body to glucose, a simple sugar

Glucose

• A simple sugar manufactured by the body from carbohydrates, fat, and to a lesser extent protein, which serves as the body's main source of fuel

• Glucose is absorbed and transported in the blood

• Circulates in blood until it enters cells with the aid of insulin

• Either used or stored as energy

Glycogen

• The complex carbohydrate molecule used to store carbohydrates in the liver and muscle cells

• When carbohydrate energy is needed, glycogen is converted into glucose for use by the muscle cells

• Stored in the liver and muscle cells

Fat

• One of the three main classes of foods and a source of energy in the body

• Helps the body use some vitamins

• Keeps the skin healthy• Serves as energy stores

for the body

Fat

• Two types of fats in food, saturated and unsaturated

• Benefit of fat as a fuel source is that most people have inexhaustible supply of fat:– Can be broken down into

triglycerides– Used for energy during

prolonged physical activity or exercise

FatsSaturated Fats• Solid at room temperature• Derived from animal products• Some plant sources – coconut palm• Raise LDL Cholesterol (bad Cholesterol)Unsaturated Fats• Liquid at room temperature• Derived from vegetables & plants (olive oil,

nuts, peanut oil, canola oil)• Lowers LDL and maintains HDL

Triglycerides

The chemical or substrate form in which most fat exists in food as well as in the body.

• Formed from fats eaten in foods or made in the body from other energy sources such as carbohydrates

• When calories are not immediately needed they are converted to triglycerides

• Transported to fat cells where they are stored

Protein

Amino acids linked by peptide bonds• Consist of carbon,

hydrogen, nitrogen, oxygen, and usually sulfur, and have several essential biologic compounds

• Rarely supplies much energy during exercise

Protein

• Is sometimes ignored as a significant fuel for energy metabolism

• Becomes a significant source of fuel in starvation situations

Gluconeogenesis

The formation of glucose from noncarbohydrate sources, such as amino acids• During negative energy balance, amino acids

are used to assist in energy production

Energy and Mechanical Work

Forms of exercise can be defined by:• Intensity• Duration

– Understanding this relationship will help to determine which energy system one is using at different intensities and durations of exercise

Energy and Muscle Contraction

• Energy is used to form the myosin-actin cross-bridges that facilitate muscle contraction

• At these cross-bridges is an enzyme that separates a phosphate from the ATP, releasing energy

Energy Systems and Work

Energy Systems in the Body• Stored Adenosine Triphosphate

System(Stored ATP)―energy storage and transfer unit within the cells of the body– Adenosine Diphosphate (ADP)―a high-energy

compound occurring in all cells from which adenosine triphosphate (ATP) is formed

Adenosine Triphosphate

When the enzyme ATPase combines with an ATP molecule, it:• Splits the last phosphate group away• Releases large amount of free energy• What remains is ADP and an inorganic

phosphate molecule (Pi)

ATP as Energy

ATP-PC System

• A phosphate is transferred from another high-energy molecule called phosphocreatine to an ADP molecule

• Fast, High Energy, without oxygen (anaerobic)• Utilized for quick intense activities lasting 10-15 seconds

in duration

Anaerobic Glycolysis System

Anaerobic Glycolysis System• Anaerobic means of

producing ATP• Through chemical

breakdown of glucose• A process referred to as

anaerobic glycolysis• This system will be utilized

for events lasting 30-50 seconds in duration

Oxidative System

• Most complex of energy systems

• Utilized for events lasting longer than 50 seconds

• Uses substrates with the aid of oxygen to generate ATP– With Oxygen (aerobic)

• Three oxidative or aerobic systems:– Aerobic glycolysis– The Krebs cycle– The electron transport chain

(ETC)

Energy During Exercise

• Most important factors regulating energy utilization during exercise is:– Intensity– Duration

• Intensity and duration of exercise are inversely related• As duration of exercise increases (up to approximately

2 minutes), the primary source of energy comes from glucose

• With longer exercise the main fuel source will switch to fats

Energy During Exercise

Steady-State Exercise

Bioenergetics of exercise can be indirectly measured in a laboratory using:• Treadmill• Cycle ergometer• Rowing ergometer• Cross-country ski simulator• Swimming flume

Steady-State Exercise

• During these modes of exercise, the concentrations of oxygen and carbon dioxide and volume of expired air are measured

• Other physiologic functions can be measured:– Heart rate– Blood pressure– Exercise load– Work output

Steady-State Exercise

When client finishes exercise:• Energy demands fall back to baseline quickly • Oxygen consumption remains elevated for a

short period to keep generating ATP aerobically

• Excess postexercise oxygen consumption (EPOC) ―the state in which the body’s metabolism is elevated after exercise

Steady-State Exercise

Intermittent Work

During intermittent exercise:• Client will experience

increase in intensity• Followed by recovery• The work to rest ratio

tends to be short– It will take approximately

90 seconds to replenish the ATP-PC system.

Estimating Fuel Contribution

Fat-Burning Zone Myth

• Low-Intensity Exercise• 20 minutes of walking at 3.0 mph, RQ of .80– 67% from fats– 33% from carbs

• 4.8 calories per minute– 3.2 calories from fat– 1.6 from carbs

• 64 calories from fat• 32 calories from carbs

Fat-Burning Zone Myth

• High-Intensity Exercise• 20 minutes of walking at 6.0 mph, RQ of .86– 46% from fats– 54% from carbs

• 9.75 calories per minute– 4.48 calories from fat– 5.2 from carbs

• 90 calories from fat• 104 calories from carbs

Fat-Burning Zone Myth

• Some marketing departments of exercise equipment have misinterpreted concept

• The inaccuracy is that people burn more fat at lower-intensity exercise because such easy work does not require getting energy quickly from carbohydrates

• The concept is logical but the science is flawed