Bioenergetics, Exercise Metabolism, and Hormonal Responses to Exercise

Flashcards covering key terms and definitions related to bioenergetics, exercise metabolism, and hormonal responses to exercise based on the lecture notes.

Metabolism

The sum of all chemical reactions that occur in the body.

Anabolism

The synthesis of molecules.

Catabolism

The breakdown of molecules.

Bioenergetics

A metabolic process in which foodstuffs (carbohydrates, proteins, and fats) are turned into energy currency (ATP).

Endergonic reactions

Chemical reactions that require energy to be added and are endothermic (absorb heat).

Exergonic reactions

Chemical reactions that release energy and are exothermic (release heat or light).

Coupled reactions

Reactions where the energy liberated from exergonic reactions fuels the energy requirements of endergonic reactions.

Carbohydrates (fuel)

Provide readily available energy and yield 4 kcal/gram.

Fats (fuel)

Provide energy best suited for extended lengths of exercise and yield 9 kcal/gram.

Proteins (fuel)

Provide essential amino acids and yield 4 kcal/gram.

ATP (Adenosine Triphosphate)

An essential and universal energy source for all cells, made up of an adenine portion, a ribose portion, and three linked high-energy phosphates.

Rate-limiting enzymes

Specific enzymes throughout bioenergetic pathways that regulate the rate of ATP production to match the body's energy demands.

Anaerobic pathways

Metabolic pathways that do not require oxygen; they are fast but produce less energy and are not sustainable over long periods.

ATP-PC (Phosphagen) system

The simplest and most rapid anaerobic method to produce ATP, where phosphocreatine donates a high-energy phosphate group to ADP to resynthesize ATP.

Creatine Kinase

The enzyme that catalyzes the reaction in the phosphocreatine (PC) system (PC + ADP → ATP + C).

Glycolysis

The second anaerobic pathway, a multistep process involving the breakdown of glucose or glycogen into two molecules of pyruvic acid (pyruvate) or lactic acid (lactate), producing a net gain of two ATP.

Pyruvic acid (pyruvate)

A product of glycolysis, which can be converted to lactic acid (lactate) in anaerobic conditions.

Lactic acid (lactate)

A product of glycolysis, especially during high-intensity anaerobic exercise.

Aerobic pathways

Metabolic pathways that require oxygen and occur in the mitochondria of cells; they are slower to initiate but produce significantly more energy and are sustainable over extended periods.

Citric Acid Cycle (CAC) / Krebs cycle

An aerobic process that completes the oxidation of organic molecules, using NAD+ and FAD to carry electrons to the Electron Transport Chain.

Electron Transport Chain (ETC)

An aerobic process that shuttles electrons across protein complexes to create a concentration gradient of H+, which is used to power ATP production by ATP Synthase, with oxygen as the ultimate electron acceptor.

NADH

A by-product of aerobic and anaerobic pathways used in the ETC to generate 2.5 ATP.

FADH2

A by-product of aerobic pathways used in the ETC to generate 1.5 ATP.

Phosphofructokinase (PFK)

The most important rate-limiting enzyme in glycolysis, stimulated by AMP, ADP, Pi, and increased pH, and inhibited by ATP, CP, citrate, and decreased pH.

Phosphorylase

An enzyme that breaks down glycogen into glucose, which then enters glycolysis; stimulated by Ca++ and Epinephrine.

Isocitrate dehydrogenase

The rate-limiting enzyme in the Citric Acid Cycle, stimulated by ADP, Ca++, and NAD+, and inhibited by ATP and NADH.

Cytochrome C oxidase

The rate-limiting enzyme in the Electron Transport Chain, stimulated by ADP and Pi, and inhibited by ATP.

Oxygen deficit

The lag in oxygen uptake at the onset of exercise when anaerobic processes are engaged to meet immediate energy demands.

Steady state (exercise)

The point during exercise when oxygen consumption matches oxygen demand, and ATP production is primarily accomplished aerobically.

Metabolic inertia

The delay in the activation of aerobic pathways at the onset of exercise due to insufficient concentrations of stimulating molecules.

Excess Post-Exercise Oxygen Consumption (EPOC)

The amount of oxygen consumed above rest after a workout, characterized by rapid and slow components.

Rapid component of EPOC

The phase where excess oxygen is used to restore phosphocreatine in muscles and replenish oxygen stores in blood and tissues.

Slow component of EPOC

The phase where elevated heart rate, breathing, body temperature, and high epinephrine/norepinephrine levels require additional oxygen, and O2 is needed for gluconeogenesis.

Gluconeogenesis

The process of synthesizing new glucose in the liver, often from precursors like lactate, amino acids, and glycerol.

Cori Cycle

A metabolic pathway where lactate produced by skeletal muscles is transported to the liver, converted to glucose via gluconeogenesis, and then returned to the working muscles as fuel.

VO2 max (Maximal Oxygen Uptake)

A physiological ceiling for the ability of the oxygen transport system to deliver oxygen to contracting muscles; the point where increased workload does not result in higher O2 consumption.

Lactate Threshold (LT)

The point during increasing exercise intensity where the concentration of lactate in the blood begins to rise at an exponential rate.

Respiratory Exchange Ratio (RER)

The ratio of carbon dioxide produced to oxygen consumed (VCO2/VO2) during exercise, used to estimate the involvement of carbohydrates and fats in energy production.

Respiratory Quotient (RQ)

The RER measured under steady-state conditions, representing the cellular substrate utilization.

Crossover point

The point in incremental exercise (typically between 30 and 40% VO2 max) where the primary fuel source shifts from fats to carbohydrates.

Lipolysis

The biochemical breakdown of triglycerides into Free Fatty Acids (FFAs) and glycerol.

Lipases

Enzymes that break down fats (triglycerides); their activity is stimulated by hormones like epinephrine, norepinephrine, and glucagon, and inhibited by increased lactate concentrations.

Insulin

A hormone that inhibits lipase activity and reduces the mobilization of Free Fatty Acids (FFA).

Muscle glycogen

Stored carbohydrate in muscles, providing a direct source of energy, especially during high-intensity exercise.

Liver glycogen

Stored carbohydrate in the liver, serving as a means of replacing blood glucose.

Free Fatty Acids (FFA)

The primary fuel source derived from fat (triglycerides), particularly dominant during low-intensity exercise.

Glycogenolysis

The process of glycogen breakdown, initiated by mechanisms such as epinephrine binding to β-adrenergic receptors activating cyclic AMP (cAMP) or intracellular calcium (Ca++) activating calmodulin.

Calmodulin

An enzyme activated by calcium (Ca++) release during muscle contraction, which increases the activity of other enzymes that stimulate glycogenolysis.

Permissive/Slow-acting hormones

Hormones that establish overall metabolic rate and are necessary for other hormones to act; includes thyroid hormones, cortisol, and growth hormone.

Fast-acting hormones

Hormones that have rapid action to return plasma glucose levels to normal; includes epinephrine, norepinephrine, insulin, and glucagon.

Thyroid hormones (T3 and T4)

Permissive hormones important for establishing the overall metabolic rate and necessary for many other hormones to act.

Cortisol

The primary glucocorticoid that stimulates FFA mobilization, mobilizes tissue protein for gluconeogenesis, and decreases the rate of glucose utilization by cells.

Growth Hormone (GH)

A hormone involved in tissue protein synthesis that supports cortisol's action in preserving plasma glucose by decreasing glucose uptake, increasing FFA mobilization, and enhancing gluconeogenesis.

Epinephrine and Norepinephrine (E/NE)

Catecholamine hormones that maintain plasma glucose by mobilizing glucose from the liver and FFA from adipose tissue, and interfering with glucose uptake by tissues.

Glucagon

A counter-regulatory hormone to insulin, whose levels rise during exercise to favor the mobilization of FFA from adipose tissue and glucose from the liver.

G/I ratio (Glucagon to Insulin ratio)

A ratio that accounts for most of the glucose mobilized from the liver during moderate and vigorous physical exercise; a higher ratio increases hydrolysis and gluconeogenesis.

Hormone Sensitive Lipase (HSL)

An enzyme in adipose tissue that breaks down triglycerides into FFA and glycerol, under stronger hormonal control at higher exercise intensities, and inhibited by elevated lactate and H+ levels.