Human Energy Transfer and Physical Activity

Vocabulary practice flashcards covering human bioenergetics, thermodynamics, cellular metabolism, glycolysis, mitochondrial energy transfer, and recovery dynamics.

Bioenergetics

The study of how the body obtains, transforms, stores, and uses energy to perform biological work.

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed, but only transformed from one state to another without being depleted.

Exergonic Reactions

Physical or chemical processes that release energy to their surroundings; described as "downhill" processes that produce a decline in free energy.

Endergonic Reactions

Chemical processes that store or absorb energy; described as "uphill" processes that proceed with an increase in free energy for biologic work.

Second Law of Thermodynamics

The tendency of potential energy to convert into kinetic energy of motion with a lower capacity for work, ultimately degrading to an unusable form of kinetic or heat energy.

Enzymes

Highly specific, large protein catalysts that accelerate the forward and reverse rates of chemical reactions without being consumed or altered.

Coenzymes

Complex nonprotein substances that facilitate enzyme action by binding a substrate with its specific enzyme.

Enzyme Mode of Action

The process by which an enzyme's active site matches a specific substrate to form an enzyme-substrate complex, hydrolyzes or splits it to yield products, and emerges unchanged to interact with subsequent substrates.

Adenosine Triphosphate (ATP)

The cell's energy "currency" that provides the required chemical energy for all cellular functions and powers biological work; degrading one mole of ATP to ADP liberates $7.3\,\text{kcal}\cdot\text{mol}^{-1}$ of free energy.

ATP-Phosphocreatine (PCr) System

An immediate, anaerobic energy pathway where the hydrolysis of phosphocreatine releases energy to rapidly rebind ADP and inorganic phosphate into ATP during high-intensity, brief-duration efforts.

Creatine Kinase

The enzyme (also called creatine phosphokinase) that regulates the rate of phosphagen breakdown to resynthesize ATP from PCr.

Fast Glycolysis

A short-term anaerobic energy pathway consisting of 10 enzymatically controlled reactions that breaks down glucose into two pyruvate molecules, yielding a net of $2\text{ ATP}$ and forming lactate.

Phosphofructokinase (PFK)

The rate-limiting enzyme that regulates the reaction sequence in fast glycolysis.

Cori Cycle

A liver-based biochemical pathway that clears lactate from the blood and synthesizes it back into glucose via gluconeogenesis, which can then be delivered back to skeletal muscle.

Monocarboxylate Transporters (MCT)

Intracellular lactate shuttles that transport lactate produced in fast-twitch fibers to other muscle fibers for conversion into pyruvate and entry into aerobic metabolism.

Slow Glycolysis

Aerobic carbohydrate breakdown occurring at lower or steady-state exercise intensities that yields $2\text{ pyruvate}$ and $2\text{ NADH}$ without producing net lactate.

Aerobic Metabolism (Two Phases)

Mitochondrial energy production where Phase 1 generates $H^+$ during acetyl-CoA breakdown in the citric acid cycle, and Phase 2 regenerates substantial ATP as reduced coenzyme complexes become oxidized in the electron transport chain.

Beta (\beta) Oxidation

The catabolic process that breaks down fatty acids into 2-carbon acyl-CoA molecules within the mitochondria to enter the citric acid cycle.

"Fats Burn in a Carbohydrate Flame"

The biochemical concept that fatty acid breakdown depends on carbohydrate breakdown; depleting carbohydrates lowers pyruvate and oxaloacetate levels, which reduces the citric acid cycle's capacity to process acetyl-CoA.

Oxidation

A chemical reaction that involves the loss of electrons, encapsulated in the mnemonic "OIL" (Oxidation Involves Loss).

Reduction

A chemical reaction that involves the gain of electrons, encapsulated in the mnemonic "RIG" (Reduction Involves Gain).

Deamination

The removal of an amine group from an amino acid molecule, forming ammonia ($\text{NH}_3$), which the liver then converts to urea for excretion.

Transamination

The enzymatic transfer of an amino group from an amino acid to a ketoacid.

Wingate Test

A 30-second anaerobic performance test used to assess peak power, relative power, anaerobic fatigue, rate of fatigue, and anaerobic capacity.

Blood Lactate Threshold

The exercise intensity at which blood lactate concentration begins to increase exponentially above baseline; typically occurs at around $55\%$ of maximal aerobic capacity in untrained individuals.

Onset of Blood Lactate Accumulation (OBLA)

The defined blood lactate threshold point of $4\,\text{mmol}$, where blood lactate accumulation significantly outpaces clearance and muscle fatigue occurs.

Steady-Rate Aerobic Metabolism

A plateaued state in oxygen consumption ($\text{VO}_2$) representing a balance between the body's energy requirements and aerobic ATP production without net blood lactate accumulation.

Oxygen Deficit

The difference between total oxygen uptake ($\text{VO}_2$) during physical activity and the amount that would have been consumed had steady-rate aerobic metabolism been reached immediately from the start.

Maximal Oxygen Uptake (\text{VO}_2\text{max})

The highest rate of oxygen consumption achieved despite further increases in exercise intensity, indicating an individual's maximal capacity for aerobic ATP resynthesis.

Type II Muscle Fibers

Fast-twitch fibers with rapid contraction velocity and high glycolytic anaerobic capacity; they appear unstained under histochemical analysis for ATPase activity.

Type I Muscle Fibers

Slow-twitch fibers with slower contraction velocities that primarily produce energy aerobically for continuous activities; they stain dark for ATPase activity.

Excess Post-Exercise Oxygen Consumption (EPOC)

The excess oxygen consumed above resting baseline levels during recovery to restore the body's physiological and biochemical processes to pre-exercise status (historically termed "oxygen debt").