Bioenergetics, Substrates, and Metabolic Regulation

Vocabulary flashcards covering key terms and concepts in exercise physiology, substrate utilization, bioenergetics, and neuromuscular/endocrine systems.

calorie (cal)

Amount of heat energy required to raise the temperature of $1\,\text{g}$ of water by $1\,^\circ\text{C}$.

kilocalorie (kcal)

An energy unit equivalent to $1{,}000\,\text{cal}$ or $1\,\text{Calorie (Cal)}$.

Carbohydrate Energy Yield

Yields $4.1\,\text{kcal}\cdot\text{g}^{-1}$ and serves as the primary substrate for moderate-to-high intensity exercise.

Dietary Fat Energy Yield

Yields $9.4\,\text{kcal}\cdot\text{g}^{-1}$ and serves as the main energy source during rest and low-intensity exercise, providing the highest yield but slowest rate of ATP synthesis.

Protein Energy Yield

Yields $4.1\,\text{kcal}\cdot\text{g}^{-1}$ with a minor contribution ($<5\%{-}10\%$), utilized primarily during prolonged starvation or extreme exercise via gluconeogenesis.

Liver Glycogen Depot

A carbohydrate storage depot in the body containing $\sim 110\,\text{g}$ ($451\,\text{kcal}$).

Muscle Glycogen Depot

A carbohydrate storage depot in the body containing $\sim 500\,\text{g}$ ($2{,}050\,\text{kcal}$).

Glucose in Body Fluids Depot

A carbohydrate storage depot in the body containing $\sim 15\,\text{g}$ ($62\,\text{kcal}$).

Enzymes

Protein catalysts that lower the activation energy required for biochemical reactions without altering overall energy yield or equilibrium.

Respiratory Exchange Ratio (RER)

The ratio of carbon dioxide production to oxygen consumption, calculated as $\text{RER} = \frac{\text{VCO}_2}{\text{VO}_2}$.

Pure Fat Oxidation

Substrate utilization condition ($100\%$ Fat) corresponding to an $\text{RER} = 0.70$ and an energy yield of $4.69\,\text{kcal}\cdot\text{L O}_2^{-1}$.

Mixed Substrates Oxidation

Substrate utilization condition ($50\%$ Fat / $50\%$ Carbohydrate) corresponding to an $\text{RER} = 0.85$ and an energy yield of $4.86\,\text{kcal}\cdot\text{L O}_2^{-1}$.

Pure Carbohydrate Oxidation

Substrate utilization condition ($100\%$ CHO) corresponding to an $\text{RER} = 1.00$ and an energy yield of $5.05\,\text{kcal}\cdot\text{L O}_2^{-1}$.

Free Fatty Acid (FFA) Beta-Oxidation

The mitochondrial process that cleaves FFA carbon chains into 2-carbon Acetyl-CoA molecules prior to entering the Krebs cycle, requiring an upfront activation expenditure of $2\,\text{ATP}$ and yielding high net ATP totals (e.g., palmitic acid yields $129\,\text{net ATP}$).

Lactate Threshold (LT)

The exercise intensity at which blood lactate concentration increases systematically above baseline levels ($50\%{-}60\%\,\text{VO}_{2\text{max}}$ in untrained; $65\%{-}80\%\,\text{VO}_{2\text{max}}$ in trained athletes).

Factors Determining Muscle Oxidative Capacity

1. Oxidative enzyme activity (high levels of Succinate Dehydrogenase [SDH] and Citrate Synthase). 2. Muscle fiber type composition (higher proportion of Type I slow-twitch fibers with elevated mitochondrial volume and density). 3. Endurance training adaptations.

Homeostasis

Maintenance of a constant and normal internal environment during resting, unstressed conditions.

Steady State

Maintenance of a constant internal environment during exercise or environmental stress where body demands equal physiological responses, though values differ from resting baseline.

Acute Responses

Immediate, short-term physiological adjustments to a single bout of exercise.

Chronic Adaptations

Long-term functional and structural modifications resulting from repeated exercise training over time.

Mechanical Work Formula

$$\text{Work (J)} = \text{Force (N)} \times \text{Distance (m)}$$

Mechanical Power Formula

$$\text{Power (W)} = \frac{\text{Work (J)}}{\text{Time (s)}}$$

Resting Potential

Maintenance of internal negative potential ($\sim -70\,\text{mV}$) governed by the $\text{Na}^+/\text{K}^+$ pump ($3\,\text{Na}^+$ out / $2\,\text{K}^+$ in).

Neuro Signal Direction

Dendrites $\rightarrow$ Soma (Cell Body) $\rightarrow$ Axon $\rightarrow$ Axon Terminal.

Sensory Neurons (Afferent)

Neurons that carry incoming signals from peripheral sensory receptors to the central nervous system (CNS).

Steroidal Hormones

Lipid-soluble hormones derived from cholesterol that directly cross cell membranes to bind intracellular/nuclear receptors and initiate direct gene transcription.

Non-Steroidal Hormones

Non-lipid soluble hormones (proteins/peptides/amino acids) that bind outer cell-surface receptors and act via second-messenger systems (e.g., cyclic AMP).

ATP-PCr System

Energy system utilized during explosive efforts lasting $<15\,\text{s}$.

Anaerobic Glycolysis

Energy system utilized during high-intensity efforts lasting $15\,\text{s}$ to $2\,\text{min}$.

Aerobic Oxidative System

Energy system utilized during sustained endurance activities lasting $>2\,\text{min}$.

Open Window Hypothesis

The concept that prolonged intense exertion or overtraining causes transient immunosuppression, temporarily increasing infection risk.