Fuel for Exercise: Bioenergetics and Muscle Metabolism

Vocabulary flashcards covering key bioenergetics concepts, energy systems, substrate metabolism, and muscle energetics from Chapter 2.

Bioenergetics

The chemical pathways in the body that convert substrates into usable energy.

Metabolism

The sum of all chemical reactions that occur within the human body.

Energy Substrates

Macronutrients—carbohydrates, fats, and proteins—that are chemically converted by the body into usable energy.

Gluconeogenesis

The metabolic process by which protein or amino acids are converted into glucose to be used for energy.

Lipogenesis

The metabolic process by which protein or amino acids are converted into fatty acids.

Catabolism

The metabolic breakdown of large compounds, such as macronutrients, into smaller ones to release energy.

Enzymes

Protein molecules that speed up catabolic chemical reactions without being consumed in the process.

Adenosine Triphosphate (ATP)

The primary energy molecule composed of adenosine and three phosphate groups that powers all cellular functions in the body.

Phosphorylation

The chemical addition of a phosphate group to adenosine diphosphate ($\text{ADP}$) to synthesize adenosine triphosphate ($\text{ATP}$).

ATP-PCr System

A simple, anaerobic energy pathway that breaks down phosphocreatine stored in muscle cells to rapidly synthesize $\text{ATP}$ during high-intensity exercise lasting $3\text{ to }15\,\text{seconds}$.

Creatine Kinase

The enzyme that catalyzes the release of energy from phosphocreatine ($\text{PCr}$), whose activity is stimulated by increased $\text{ADP}$ levels and inhibited by increased $\text{ATP}$ levels.

Glycolysis

The anaerobic pathway that breaks down glucose or stored glycogen using glycolytic enzymes to produce $2\text{ to }3\,\text{ATP}$, supporting high-intensity exercise lasting $1\text{ to }2\,\text{minutes}$.

Glycogenolysis

The enzymatic conversion and breakdown of stored glycogen from the liver or muscles into glucose.

Lactate

The non-acidic end product of anaerobic glycolysis produced primarily in Type 2 muscle fibers, which can be transported into mitochondria (especially in Type 1 fibers) to undergo oxidative metabolism.

Oxidative System

The complex, aerobic energy system (cellular respiration) occurring in the mitochondria that utilizes oxygen to produce large quantities of $\text{ATP}$ from carbohydrates or fats.

Cellular Respiration

The process through which cells break down energy substrates in the presence of oxygen within the mitochondria to yield energy.

Lipolysis

The enzymatic breakdown of triglycerides stored in fat cells or muscle fibers into $1\text{ glycerol}$ and $3\text{ free fatty acids (FFAs)}$, catalyzed by lipases.

Beta-Oxidation

The initial series of reactions in fat metabolism that converts free fatty acids into Acetyl $\text{CoA}$ prior to entering the Krebs Cycle.

Crossover Concept

The physiological phenomenon describing how fat is the dominant energy substrate at rest and low intensities, whereas carbohydrate utilization progressively increases and becomes dominant as exercise intensity rises.

Interaction of Energy Systems (Rate vs. Yield)

The inverse relationship where anaerobic systems ($\text{PCr}$ and glycolysis) generate $\text{ATP}$ at very high rates but with limited available capacity, whereas oxidative systems generate $\text{ATP}$ at lower maximal rates but with virtually unlimited total energy capacity.

Oxidative Capacity of Muscle

A muscle's maximal capacity for aerobic energy production, determined by enzyme concentration/activity, fiber type composition (e.g., higher mitochondria in Type 1 fibers), and overall oxygen availability.