Energy Expenditure, Fatigue, and Muscle Soreness

Comprehensive vocabulary flashcards covering energy expenditure, calorimetry, gas exchange parameters, muscle fiber recruitment, fatigue mechanisms, muscle soreness, and heat cramps.

Metabolic Rate

The rate of energy use by the body.

Basal Metabolic Rate (BMR)

The rate of energy expenditure at rest, assessed in the supine position in a thermoneutral environment after $8\text{ h}$ of sleep and $12\text{ h}$ of fasting.

Direct Calorimetry

A method that gauges energy production by measuring heat production inside an insulated calorimeter, where body heat warms circulating water.

Indirect Calorimetry

A method that estimates total body energy expenditure based on respiratory gas exchange by measuring the concentrations of oxygen ($\text{O}_2$) consumed and carbon dioxide ($\text{CO}_2$) produced.

$$\dot{\text{V}}\text{O}_2\text{max}$$

The highest rate of oxygen consumption attainable during maximal or exhaustive exercise, primarily indicated by a plateau in $\text{VO}_2$ despite increasing exercise intensity.

$$\dot{\text{V}}\text{O}_2$$

The volume of oxygen consumed per minute, calculated as the volume of inspired $\text{O}_2$ minus the volume of expired $\text{O}_2$.

$$\dot{\text{V}}\text{CO}_2$$

The volume of carbon dioxide produced per minute, calculated as the volume of expired $\text{CO}_2$ minus the volume of inspired $\text{CO}_2$.

Respiratory Exchange Ratio (RER)

The ratio between the rate of carbon dioxide produced and oxygen consumed ($\text{RER} = \dot{\text{V}}\text{CO}_2 / \dot{\text{V}}\text{O}_2$), which reflects fuel substrate utilization during metabolism.

Crossover Concept

The physiological principle describing the progressive transition from fat oxidation to carbohydrate (CHO) oxidation as exercise intensity increases.

Oxygen Deficit

The lag in oxygen uptake at the onset of exercise where oxygen demand exceeds oxygen consumption, reflecting initial ATP production through anaerobic pathways.

Steady-State Oxygen Consumption

The physiological state in which oxygen consumption matches the oxygen demand of ongoing exercise, indicating ATP generation via aerobic pathways.

Excess Postexercise Oxygen Consumption (EPOC)

The elevated oxygen uptake above resting levels during recovery that repays the oxygen deficit, replenishes ATP and PCr stores, converts lactate to glycogen, reloads myoglobin and hemoglobin, and clears carbon dioxide.

Fatigue

A decrease in muscular performance with continued effort accompanied by sensations of tiredness, or the inability to maintain the required power output to continue muscular work at a given intensity.

Phosphocreatine (PCr) Depletion

The rapid exhaustion of intramuscular phosphocreatine reserves during short-term, high-intensity exercise that directly induces muscular fatigue.

Glycogen Depletion

The depletion of intramuscular and liver glycogen stores during prolonged or high-intensity exercise, which, alongside hypoglycemia, contributes to exhaustion.

Type I Muscle Fibers

Slow-twitch muscle fibers that are recruited first during low- to moderate-intensity exercise and undergo the fastest depletion when utilized most frequently.

Type IIa Muscle Fibers

Fast-twitch muscle fibers that are recruited second after Type I fibers during moderate- to high-intensity muscular efforts.

Type IIx Muscle Fibers

Fast-twitch glycolytic muscle fibers that are recruited last during maximal-intensity muscular exertion.

Neuromuscular Junction Fatigue

Neural transmission failure that impedes muscle activation, caused by reduced acetylcholine (ACh) release or altered muscle resting membrane potentials.

Lactate

The ionized byproduct of anaerobic glycolysis that dissociates from lactic acid, buffers intracellular acidity by binding free protons, and serves as an oxidizable fuel during oxygen shortage.

Hydrogen Ion ($\text{H}^+$) Accumulation

The buildup of acidic protons from rapid anaerobic ATP hydrolysis that lowers muscle pH (acidosis), creating a burning sensation and inhibiting muscular contraction.

Micro-Fiber Tears

Microscopic structural damage within skeletal muscle fibers that stimulates muscle repair and hypertrophy, becoming symptomatic $12\text{–}24\text{ hours}$ post-exercise and peaking at $24\text{–}72\text{ hours}$.

Acute Muscle Soreness

Muscle soreness occurring during or immediately following novel or strenuous exercise, caused by hydrogen ion accumulation and interstitial tissue edema.

Delayed-Onset Muscle Soreness (DOMS)

Muscular soreness and stiffness manifesting $1\text{ to }2\text{ days}$ post-exercise, predominantly triggered by eccentric contractions and structural micro-tears rather than elevated blood lactate.

Heat Cramps

Severe, involuntary muscle spasms associated with significant sweat losses, electrolyte depletion (predominantly sodium and chloride), and dehydration.