Fuel for Exercise: Review of Substrates (EXSC 3319)

Vocabulary-style flashcards covering key terms from the lecture notes on energy substrates, energy systems, and metabolic regulation.

E-C Coupling

The process by which an electrical signal (action potential) triggers Ca2+ release in muscle cells, leading to cross-bridge cycling and contraction.

Sliding Filament Theory

Actin (thin) filaments slide past myosin (thick) filaments during contraction, shortening the sarcomere.

Length-Tension Relationship

The relationship between muscle length and the tension it can produce; there is an optimal sarcomere length for maximum force.

Type I Fibers

Slow-twitch muscle fibers with high oxidative capacity; fatigue-resistant and endurance-oriented.

Type II Fibers

Fast-twitch muscle fibers that generate more force but fatigue more quickly; subtypes include IIa and IIx.

Energy Substrates

Carbohydrates, fats, and proteins used to produce ATP in the body.

Carbohydrates

Converted to glucose; primary energy source for muscles and brain; stored as glycogen in liver and muscle.

Fats

Stored energy source that, when broken down from triglycerides, yields glycerol and free fatty acids for ATP production.

Proteins

Minor energy source; amino acids can be used for energy via gluconeogenesis; can contribute up to about 10% of energy during exercise.

Bioenergetics

Chemical pathways within cells that convert substrates to energy.

Metabolism

Chemical reactions in the body that maintain life, including both anabolic and catabolic processes.

ATP

Adenosine triphosphate; the immediate energy currency of the cell.

Phosphocreatine (PCr)

A high-energy phosphate compound in muscle that rapidly donates phosphate to ADP to regenerate ATP during short, high-intensity effort.

ATP-PCr System

The immediate energy system using stored ATP and PCr to quickly regenerate ATP in the first seconds of exercise.

Anaerobic Metabolism

Energy production that does not require oxygen; includes ATP-PCr and glycolysis.

Glycolytic System (Glycolysis)

Breakdown of glucose to pyruvate (or lactate under anaerobic conditions) to rapidly produce ATP.

Oxidative System (Oxidative Phosphorylation)

Aerobic energy production in mitochondria that uses oxygen to generate large amounts of ATP.

Aerobic Metabolism

Energy production that requires oxygen and predominates during endurance activities.

Glucose

Simple sugar transported in blood; primary substrate for glycolysis.

Glycogen

Stored form of glucose in liver and muscle.

Glycogenolysis

Breakdown of glycogen to glucose for energy.

Glycogenesis

Synthesis of glycogen from glucose for storage.

Lipolysis

Breakdown of triglycerides into glycerol and free fatty acids.

Free Fatty Acids (FFA)

Fatty acids released from triglycerides for oxidation to produce ATP.

Triglycerides

Stored fat consisting of glycerol and three fatty acids; major long-term energy source.

Glycerol

Backbone molecule released during triglyceride breakdown; can be used for energy production.

Lipogenesis

Synthesis of fatty acids and fat storage from excess energy sources.

Gluconeogenesis

Production of glucose from non-carbohydrate sources (e.g., amino acids, glycerol), mainly in the liver.

Amino Acids

Building blocks of proteins; can be used for energy via gluconeogenesis in starvation.

Activation Energy

Minimum energy required to start a chemical reaction; enzymes lower this barrier.

Enzymes

Proteins that speed up chemical reactions by lowering activation energy; often end with the suffix -ase.

Rate-Limiting Enzyme

The slowest step in a metabolic pathway that largely determines the overall rate; often controlled by negative feedback.

Negative Feedback

Regulatory mechanism where the end product inhibits an earlier step to maintain balance.

Mass Action Effect

Change in pathway flux caused by differences in substrate availability; higher availability shifts usage toward that substrate.

Crossover Concept

The shift from fat to carbohydrate metabolism as exercise intensity increases; training can alter the crossover point.

Oxidative Capacity of Muscle

The muscle’s ability to oxidize substrates via aerobic pathways, dependent on mitochondria, enzymes, and blood supply.