Principles of Exercise Metabolism & Compounds of High Phosphoryl-Transfer

Flashcards covering the overview of exercise metabolism, ATP turnover, phosphocreatine systems, and metabolic regulation mechanisms including allosteric control, covalent modification, and hormonal signaling.

Physical activity

Any movement that increases energy expenditure.

Exercise

A subset of physical activity that is structured, planned, and performed with the goal of improving fitness.

Aerobic Exercise

A type of muscle activity focused on oxygen consumption, such as running or cycling.

Anaerobic Exercise

A type of muscle activity such as sprinting or resistance training.

Intensity

The metabolic demand of muscle, often measured as a percentage of maximal oxygen consumption ($VO\_2 \text{ max}$), power output, or heart rate.

$$VO\_2 \text{ max}$$

Maximal oxygen consumption, measured as $\text{mL O}\_2/\text{kg body weight/min}$, used to define exercise intensity.

Duration

An exercise parameter measured in seconds to hours that determines the predominate metabolic pathway used.

Frequency

The number of exercise sessions per week, which influences adaptations such as mitochondrial density and enzyme expression.

Citrate synthase

An enzyme whose expression increases with exercise frequency, serving as a marker for oxidative capacity.

Myosin ATPase

An enzyme that consumes ATP to drive mechanical work during muscle contraction.

ATP concentration in muscle

Typically ranges from $\text{5–8 mmol/kg}$ muscle; it remains relatively constant during exercise despite high turnover.

Energy Buffering Systems

Systems used to maintain constant ATP concentration, including Phosphocreatine, Adenylate kinase (AK), Glycolysis, and Oxidative phosphorylation.

ATP-ADP Cycle

The continuous process of ATP hydrolysis and resynthesis; a human with a TDEE of $2,000 \text{ kcal/day}$ resynthesizes ~$45 \text{ kg}$ of ATP daily.

Phosphocreatine (PCr)

The immediate ATP buffer in skeletal muscle, providing rapid ATP regeneration during the first several seconds of intense exercise.

Creatine Kinase (CK)

An enzyme that catalyzes the conversion between PCr and creatine; it exists as isoenzymes CK-BB, CK-MM, and CK-MB.

Creatine

An amino acid obtained from the diet (meat) or synthesized from glycine, arginine, and methionine (SAM).

CK-MM

The muscle-specific isoenzyme of creatine kinase that binds to the M-line in the sarcolemma via lysines.

Phosphocreatine Shuttle System

The mechanism by which ATP produced in the mitochondria transfers phosphate back to creatine to replenish PCr stores after exercise.

Adenylate Kinase (AK)

A buffering system that converts $2 \text{ADP}$ to $\text{ATP} + \text{AMP}$ when ATP turnover is high.

AMP-activated protein kinase (AMPK)

A general energy-sensing enzyme activated by high [AMP] that increases glucose uptake and fatty acid oxidation while inhibiting anabolic pathways.

AMP Deamination

The process of converting AMP to IMP and ammonia during intense exercise to reduce [AMP] and drive the adenylate kinase reaction forward.

Allosteric regulation

An immediate mechanism of metabolic control where molecules like AMP, ADP, or ATP bind to enzymes (e.g., AMP activating PFK-1) to regulate activity.

Covalent Modification

A short-term regulatory mechanism involving phosphorylation or dephosphorylation that occurs within seconds to minutes.

Glycogen Phosphorylase

An enzyme that is activated by phosphorylation to stimulate glucose mobilization.

Glycogen Synthase

An enzyme that is inactivated by phosphorylation to stop glucose storage.

Acetyl-CoA Carboxylase

An enzyme that is inactivated by phosphorylation to stimulate fat burning.

Pyruvate Dehydrogenase

An enzyme that is activated by dephosphorylation to increase carbohydrate oxidation.

Anaplerosis

The rapid increase in concentrations of Citric Acid Cycle (CAC) intermediates in skeletal muscle during exercise to support higher energy production.

Glucagon

A hormone that activates liver gluconeogenesis when glucose levels drop during prolonged exercise.

Growth hormone and Cortisol

Hormones that rise during sustained exercise to activate lipases for fatty acid breakdown in adipose tissue.