Exam 1 Study Guide

I. Introduction to Exercise Physiology

  • Acute Response vs. Chronic Adaptation:

    • Acute response: A single bout of exercise and the immediate changes that occur. These changes can include increased heart rate, ventilation rate, and hormonal secretions.

    • Chronic adaptation: How the body changes over time with repeated exercise (training). These adaptations can include increased muscle mass, improved cardiovascular function, and enhanced metabolic efficiency.

  • Descriptive vs. Mechanistic Approaches:

    • Descriptive: Describes what happens during exercise (e.g., heart rate increases). This approach focuses on observable changes without necessarily explaining the underlying causes.

    • Mechanistic: Explains why things happen (e.g., hormonal or cellular mechanisms responsible for the increase in heart rate). This approach seeks to understand the specific physiological pathways and processes involved.

  • Myokines:

    • Myokines are cytokines produced and released by muscle cells during exercise.

    • They have effects on other organs and tissues in the body, mediating some of the health benefits of exercise. For example, myokines can promote glucose uptake in muscles, enhance fat oxidation, and reduce inflammation.

  • Homeostasis and Steady State:

    • Homeostasis: Maintenance of a stable internal environment at rest. This involves dynamic regulation of various physiological variables such as body temperature, blood pressure, and blood glucose levels.

    • Steady State: Physiological variable is unchanging, but not necessarily at resting levels (e.g., during submaximal exercise). This indicates a balance between the demands of exercise and the body's ability to meet those demands.

  • Components of a Biological Control System:

    • Sensor: Detects a change in a variable. Examples include thermoreceptors detecting changes in body temperature or chemoreceptors detecting changes in blood pH.

    • Control Center: Receives information from the sensor and initiates a response. The brain, particularly the hypothalamus, often serves as the control center.

    • Effector: Brings about the appropriate response to restore balance. Examples include sweat glands increasing sweat production to lower body temperature or the respiratory system increasing ventilation to regulate blood pH.

  • Negative Feedback:

    • The response reverses the initial disturbance in homeostasis (e.g., body temperature regulation). If body temperature rises, negative feedback mechanisms trigger sweating and vasodilation to lower temperature back to normal.

  • Adaptation vs. Acclimation:

    • Adaptation: Long-term change in response to repeated environmental stresses, resulting in improved function. These changes are typically genetic and can take generations to fully manifest.

    • Acclimation: Adaptation to environmental stresses over a relatively short period of time, typically within days or weeks. This is often reversible when the stressor is removed.

  • Exercise-induced Hormesis:

    • The principle that a low to moderate dose of a stressor (exercise) can make the body stronger. High doses may be detrimental. This concept suggests that exercise can stimulate beneficial adaptations, but excessive exercise can lead to injury and overtraining.

II. Bioenergetics & Metabolism

Bioenergetics

  • Fuel Nutrients:

    • Carbohydrates, fats, and proteins are used as fuel sources. Carbohydrates are primarily used during high-intensity exercise, while fats are the main fuel source during low-intensity exercise. Proteins play a minor role in energy production during exercise.

  • Energy Pathways:

    • The body uses several energy pathways to generate ATP, each with different characteristics in terms of speed, capacity, and fuel source. These include the ATP-PCr system (phosphagen system), glycolysis, the TCA Cycle (Krebs Cycle), the Electron Transport System (ETS) / Oxidative Phosphorylation, and the breakdown of fat (beta-oxidation).

      • The ATP-PCr system (phosphagen system) provides immediate energy by breaking down phosphocreatine to regenerate ATP. This system is dominant during very short, high-intensity activities like sprinting or weightlifting.

      • Glycolysis involves the breakdown of glucose to produce ATP and pyruvate. If oxygen is available, pyruvate enters the Krebs cycle; if not, it is converted to lactate. Glycolysis is a primary energy source for high-intensity activities lasting from a few seconds to a few minutes.

      • The TCA Cycle (Krebs Cycle) oxidizes acetyl-CoA, producing CO2CO_2, ATP, and high-energy electron carriers (NADH and FADH2). This cycle is a crucial part of aerobic metabolism.

      • The Electron Transport System (ETS) / Oxidative Phosphorylation uses the electron carriers from the Krebs cycle to create a proton gradient, which drives ATP synthase to produce large amounts of ATP. This is the primary energy pathway during endurance activities.

      • The breakdown of fat (beta-oxidation) involves breaking down fatty acids to produce acetyl-CoA, which then enters the Krebs cycle. Beta-oxidation is the dominant energy source during low-intensity, long-duration activities.

  • Oxidation-Reduction Reactions:

    • Oxidation: Removal of electrons.

    • Reduction: Addition of electrons.

    • NAD+NAD^+ is reduced to NADHNADH. FADFAD is reduced to FADH2FADH_2.

  • Carbon Dioxide Production:

    • CO2CO_2 is produced in the Krebs cycle.

    • Glucose (6 carbons), Pyruvate (3 carbons), Acetyl-CoA (2 carbons).

  • ATP Production:

    • ATP is used in the ATP-PCr system and glycolysis.

    • ATP is produced through substrate-level phosphorylation (glycolysis and Krebs cycle) and oxidative phosphorylation (ETS).

  • Oxygen Use:

    • Oxygen is the final electron acceptor in the electron transport chain (ETS), forming water.

  • Proton Gradient:

    • The flow of electrons along the inner mitochondrial membrane pumps protons from the mitochondrial matrix to the intermembrane space, creating a high concentration of H+H^+.

    • The potential energy from this gradient is then used to drive ATP synthase, which phosphorylates ADP to ATP.

  • NAD+ Replenishment:

    • Replenishment of NAD+NAD^+ is necessary for glycolysis to continue. Without it, glycolysis would stop.

  • ATP Hydrolysis:

    • ATP+H2O→ADP+Pi+H++EnergyATP + H2O \rightarrow ADP + Pi + H^+ + Energy

  • Rate Limiting Enzyme:

    • ATP-PCr: Creatine Kinase.

    • Glycolysis: Phosphofructokinase (PFK).

    • Krebs Cycle: Isocitrate Dehydrogenase.

    • ETC: Cytochrome Oxidase.

  • Fatty Acid Transport into Mitochondria:

    • Carnitine Acyltransferase I (CAT1) transports fatty acids from the cytosol into the intermembrane space of the mitochondria.

    • Carnitine Acyltransferase II (CAT2) transports fatty acids from the intermembrane space to the mitochondrial matrix.

    • Carnitine is required for this transport.

    • Malonyl-CoA inhibits CAT1, thus inhibiting beta-oxidation.

Metabolism

  • Oxygen Deficit and EPOC:

    • Oxygen Deficit: The difference between the oxygen required during exercise and the oxygen actually consumed. This occurs at the onset of exercise when the oxidative system is not yet fully activated.

    • EPOC (Excess Post-exercise Oxygen Consumption): The elevated oxygen consumption after exercise. This is due to several factors, including:

      • Variables determining EPOC:

      • Resynthesis of PCr.

      • Lactate conversion to glucose (Cori cycle).

      • Elevated body temperature.

      • Hormone levels (Epinephrine, Norepinephrine).

      • Restoration of muscle and blood oxygen stores.

    • Fast Component: Restoration of PCr and oxygen stores. This phase occurs within the first few minutes after exercise.

    • Slow Component: Lactate conversion, elevated body temperature and hormones. This phase can last for several hours after exercise.

  • Lactate Formation Benefits:

    • Lactate allows for the regeneration of NAD+NAD^+, which is necessary for continued glycolysis.

    • Lactate can be used as a fuel source in other tissues (e.g., heart, skeletal muscle).

    • Lactate can be converted back into glucose in the liver (Cori cycle).

  • Fates of Lactate:

    • Oxidation in the mitochondria of muscle fibers.

    • Transported to the liver for conversion to glucose (Cori cycle).

    • Conversion to amino acids.

  • Cori Cycle:

    • Lactate is transported from the muscle to the liver, where it is converted to glucose through gluconeogenesis; this glucose is then sent back to the muscles.

  • Glucose Paradox:

    • After prolonged endurance exercise, even though muscle glycogen stores are depleted, the rate of glucose uptake by the muscle remains high.

  • Respiratory Exchange Ratio (RER):

    • RER=VCO2/VO2RER = VCO2 / VO2

    • RER of 0.7 indicates primarily fat metabolism.

    • RER of 1.0 indicates primarily carbohydrate metabolism.

  • Factors Determining Blood Lactate Concentration:
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