NASM Chapter 4 Exercise Metabolism and Bioenergetics

  • Metabolism
    All of the chemical reactions that occur in the body to maintain itself. Metabolism is the process in which nutrients are acquired, transported, used, and disposed of by the body.
  • ***Before food can become a usable source of energy it has to be converted into small units call Substrates, Including Carbohydrates, Proteins and Fats
  • Substrates
    The material or substance on which an enzyme acts.
  • Carbohydrates
    1. Organic compounds of carbon, hydrogen, and oxygen, which include starches, cellulose, and sugars, and are an important source of energy. All carbohydrates are eventually broken down in the body to glucose, a simple sugar. 2. Neutral compounds of carbon, hydrogen, and oxygen (such as sugars, starches, and celluloses), which make up a large portion of animal foods.
  • Protein
    Amino acids linked by peptide bonds, which consist of carbon, hydrogen, nitrogen, oxygen, and usually sulfur, and that have several essential biologic compounds.
  • Fat
    One of the three main classes of foods and a source of energy in the body. Fats help the body use some vitamins and keep the skin healthy. They also serve as energy stores for the body. In food, there are two types of fats, saturated and unsaturated.
  • *** The energy stored in the substrate molecules is then chemically released in cells and stored in the form of a high-energy compound call Adenosine Triphosphae (ATP)
  • Adenosine Triphosphate (ATP)
    Energy storage and transfer unit within the cells of the body.
  • Bioenergetics
    The study of energy in the human body.
  • Exercise Metabolism
    The examination of bioenergetics as it relates to the unique physiologic changes and demands placed on the body during exercise.
  • ***The Primary end product after digestion of carbohydrates is Glucose
  • 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. (Absorbed and transported in the blood, where it circulates until it enters cells (With the aid of insulin) and is either stored or used as energy.
  • ***The Storage form of carbohydrates is called Glycogen
  • 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)
  • Triglycerides
    The chemical or substrate form in which most fat exists in food as well as in the body.
  • **Fat is a source of stored energy
  • **One of the benefits of Fat as a source of energy is that people have an inexhaustible supply of fat, which can be broken down into triglycerides and used for energy during prolonged physical activity or exercise
  • **Protein Rarely supplies energy during exercise and is often ignored as a significant source of fuel. NOTE* Protein becomes a fuel source during starvation or negative energy balance (Low calorie diet). Amino Acids are used to assist in energy production This is called- Gluconeogenesis
  • Gluconeogenesis
    The formation of glucose from noncarbohydrate sources, such as amino acids.
  • **When ATP is utilized and energy is released for cellular work (Such as a muscle contraction) it leaves behind a molecule named: (Adenosine Diphosphate ADP)
  • Adenosine Diphosphate (ADP)
    A high-energy compound occurring in all cells from which adenosine triphosphate (ATP) is formed.
  • *** One of the functions of enery metabolism is to harness enough free energy to reattach a phosphate group to an ADP and restore ATP levels back to normal to perform more work.
  • ***Energy is used to form the myosin-actin cross-bridges that facilitate muscle contraction. (For 1 cycle of a cross-bridge, 2 ATP’s are needed)
  • ***Only about 40% of the energy released from ATP is actually used for cellular work, like muscle contraction. The remainder is released as Heat
  • *** When the enzyme ATPase combines with an ATP molecule, it splits the last phosphate group away, releasing a large amount of free energy, approx 7.3 kcal per unit of ATP. Once the phosphate group has been split off, what remains is ADP and an inorganic phosphate molecule (Pi)
  • ATP ⇔ ADP + Pi + Energy Release.
  • Before ATP can release additional energy again, it must add back another phosphate group to ADP through a process called- Phosphorylation.
  • ***When all the ATP is completely depleted, there is no energy to break the connection between cross-bridges and actin active sites, and the muscle goes into Rigor
  • Rigor (Rigor Mortis)
    A sudden feeling of cold with shivering accompanied by a rise in temperature, often with copious sweating, especially at the onset or height of a fever.
  • 3 metabolic pathways in which cell can generate ATP:
    • 1. The ATP-PC system
    • 2. The Glycolytic System (Glycolysis
    • 3. The Oxidative System (Oxidative Phosphorylation)
  • ATP-PC System
    • Simplest and fastest of the energy systems.
    • Occurs without presences of oxygen (Anaerobic)
    • Provides energy for primarily high-intensity, Short duration bouts of exercise or activity (Power and Strength training)
    • Normally lasts 10-15 seconds before complete exhaustion
    • This system is always activated at the onset of activity because of its’ ability to produce energy very rapidly.
  • Glycolysis
    • Referred to commonly as anaerobic glycolysis
    • Before glucose or glycogen can generate energy it must be converted to a compound called “Glucose-6-phosphate”
    • Glycolysis does not begin until glucose or glycogen is broken down into “Glucose-6-phosphate”
    • The conversion of Glucose uses 1 ATP molecule (Glycogen does not require ATP)
    • ***The End result of glycolysis in which glucose or glycogen is broken down into either pyruvic acid (Aerobic glycolysis) or lactic acid (Anaerobic Glycolysis) is 2 ATP for each mole or unit of glucose and 3 ATP from each unit of glycogen.
    • This system can produce a significantly greater amount of energy than the ATP-PC system, it is limited to approx 30-50 seconds of duration
    • Most fitness workouts will place a greater stress on this system than the other systems because a typical repetition range of 8-12 falls within this time frame
    • NOTE*** When in the presence of oxygen, Pyruvic Acid is converted into the molcule Acetyl Coenzyme A (CoA) This is an important molecule because it contributessubstraes for the use in the second process of oxidative production of ATP, Called the Krebs Cycle. 
      • 03fig02
  • The Oxidative System
    • Most complex of the 3- uses substrates with the aid of oxygen to generate ATP
    • ***Your maximal effort was fueled initially by the ATP-PC, but your performance declines. Continued effort results in further decline, either via fast glycolysis (quick decline) or slow glycolysis (slower decline). You’re now entering the complex world of the low power but longer duration oxidative system, which is estimated to create approximately 10 calories per minute
    • The effort demand is low, but ATP in this system can be produced three ways:
      1.Krebs cycle
      2.Electron Transport Chain
      3.Beta Oxidation.

      • The Krebs cycle
        A sequence of chemical reactions that continues to oxidize the glucose that was initiated during glycolysis. Acetyl A enters the Krebs cycle, is broken down in to carbon dioxide and hydrogen, and “poof” two more ATP molecules are formed.
      • Depending on some details, the complete metabolism of a single glucose molecule produces between 35-40 ATP
      • Fat that is metabolized aerobically undergoes a process termed Beta-oxidation (b-oxidation)
      • Beta-oxidation (b-oxidation)
        The breakdown of triglycerides into smaller subunits called free fatty acids (FFAs) to convert FFAs into acyl-CoA molecules, which then are available to enter the Krebs cycle and ultimately lead to the production of additional ATP.
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  • summary: Once an ATP has been used, it must be replenished before it can provide energy again. There are three metabolic pathways as mentioned prior.
    1. The ATP-PC system
    2. The Glycolytic System (Glycolysis
    3. The Oxidative System (Oxidative Phosphorylation)


  • After 90 minutes of exercise, the majority of muscle glycogen stores are depleted. Through a combination of training and high-carbohydrate intake, it is possible to store significantly greater quantities of glycogen, perhaps up to 50% more.
  • Carbohydrate loading does NOT improve performance, it does improve training Duration.
  • *** Measurements made for the purpose of assessing exercise metabolism are typically made during periods of Steady State (Constant pace exercise)
  • *** The body prefers aerobic or oxidative metabolism because carbon dioxide and water are more easily eliminated.
  • nsca-epoc
  • Excess Postexercise Oxygen Consumption (EPOC)
    The state in which the body’s metabolism is elevated after exercise.
  • ***In a 1992 Purdue study, results showed that high intensity, anaerobic type exercise resulted in a significantly greater magnitude of EPOC than aerobic exercise of equal work output
  • Studies comparing intermittent and continuous exercise consistently show a greater EPOC response for higher intensity, intermittent exercise (Example HIIT training)
  • Recovery of the ATP-PC cycle is complete in approx 90 sec.

The Respiratory Quotient (RQ) is the amount of Carbon Dioxide (co2) expired divided by the amount of oxygen (o2) consumed. This is measured during rest or at a steady state of exercise using a metabolic analyzer

  • During Steady-state exercise, an RQ of 1.0 indicates that carbohydrate is supplying 100% of fuel, whereas an RQ of 0.7 indicates that fat is supplying 100% of fuel for metabolism.
  • Any RQ between 0.7 and 1.0 indicates a mixture of carbohydrates and fats are fueling metabolism.
  • NASM-Table-4.1
  • The fat-burning zone.
    Yes, it exists, but it has been misinterpreted. The fat-burning zone is a concept that the body burns a greater amount of fat at lower-intensity aerobic exercise than it does at higher intensities. Actually, the body burns a greater percentage of fat at lower intensities than at higher intensities. At lower intensities the body may burn 50 percent of the calories from fat, while at higher intensities it may only burn 35 percent. But at higher intensities you burn way more total calories—and more fat calories overall—than you do at lower intensities.

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