Chapter 5: Energy Expenditure

Flashcards covering Chapter 5 lecture notes on energy expenditure, direct and indirect calorimetry, metabolic calculations, BMR/RMR, aerobic capacity, EPOC, and endurance performance.

During substrate metabolism, what percentage of energy is converted into ATP versus heat?

$40\%$ of substrate energy is converted into ATP, and $60\%$ is converted into heat.

How does direct calorimetry measure energy expenditure?

It measures heat production directly by tracking the increase in water temperature as water flows through tubing embedded in the walls of a calorimeter.

What are the major disadvantages or limitations of direct calorimetry?

It is expensive, slow (cannot follow rapid changes), affected by heat from exercise equipment, prone to measurement errors caused by sweat, limited by heat stored in the body, and neither practical nor accurate for exercise.

What is indirect calorimetry, and under what metabolic condition is it accurate?

It estimates total body energy expenditure by measuring respiratory gas concentrations ($O_2$ used and $CO_2$ produced) and is accurate only for steady-state oxidative metabolism.

What is $\dot{V}O_2$ and how is it calculated?

$\dot{V}O_2$ is the volume of $O_2$ consumed per minute (rate of $O_2$ consumption), calculated as the volume of inspired $O_2$ minus the volume of expired $O_2$.

What is $\dot{V}CO_2$ and how is it calculated?

$\dot{V}CO_2$ is the volume of $CO_2$ produced per minute (rate of $CO_2$ production), calculated as the volume of expired $CO_2$ minus the volume of inspired $CO_2$.

Which six variables are required to calculate $\dot{V}O_2$ and $\dot{V}CO_2$?

Volume of inspired air, volume of expired air, fraction of oxygen in inspired air, fraction of carbon dioxide in inspired air, fraction of oxygen in expired air, and fraction of carbon dioxide in expired air.

What principle forms the basis of the Haldane transformation?

The constancy of nitrogen ($N_2$) volumes, meaning that the volume of inspired $N_2$ equals the volume of expired $N_2$ ($\dot{V}_{\text{inspired } N_2} = \dot{V}_{\text{expired } N_2}$).

What is the formula for calculating inspired volume ($\dot{V}_I$) using the Haldane transformation?

$$\dot{V}_I = \frac{\dot{V}_E \times F_E N_2}{F_I N_2}$$

How is the respiratory exchange ratio (RER) defined and calculated?

It is the ratio between the rates of $CO_2$ production and $O_2$ usage, calculated as $\text{RER} = \frac{\dot{V}CO_2}{\dot{V}O_2}$.

What is the chemical equation and resulting RER for the complete oxidation of one molecule of glucose?

$6\,O_2 + C_6H_{12}O_6 \rightarrow 6\,CO_2 + 6\,H_2O + 32\,\text{ATP}$, yielding an RER of $\frac{6\,CO_2}{6\,O_2} = 1.0$.

What is the chemical equation and resulting RER for the complete oxidation of one molecule of palmitic acid?

$23\,O_2 + C_{16}H_{32}O_2 \rightarrow 16\,CO_2 + 16\,H_2O + 129\,\text{ATP}$, yielding an RER of $\frac{16\,CO_2}{23\,O_2} = 0.70$.

What are four specific limitations of indirect calorimetry and RER measurements?

1. $CO_2$ production may not equal $CO_2$ exhalation. 2. RER is inaccurate for protein oxidation. 3. RER near $1.0$ may be inaccurate when lactate buildup alters $CO_2$ exhalation. 4. Gluconeogenesis produces an RER $< 0.70$.

Which isotopes are commonly used to study energy metabolism, and what is their primary advantage?

Carbon-13 ($^{13}C$) and deuterium ($^2H$); they offer an easy, accurate, low-risk study of $CO_2$ production that is ideal for long-term measurements over weeks.

What physiological assumption underlies heart rate monitoring for energy expenditure, and what factors confound it?

It assumes heart rate is linearly related to $\dot{V}O_2$. It is confounded by ambient temperature, upper versus lower body exercise, changes in fitness, and poor correlation at sedentary or low intensities.

What are the primary limitations of using pedometers to measure physical activity?

Inaccurate step counts at slow speeds, reading discrepancies depending on placement, failure to account for anthropometric differences, and lack of calibration.

What are the advantages and limitations of accelerometers in estimating energy expenditure?

Advantages: They detect continuous acceleration data and quantify time spent in activities of different intensities. Limitation: Inaccurate during sedentary or nonaerobic activities.

In walking prediction equations, what are the accepted energy costs for resting, horizontal, and vertical components?

Resting is $3.5\,\text{ml}\cdot\text{kg}^{-1}\cdot\text{min}^{-1}$, horizontal walking is $0.1\,\text{ml}\cdot\text{kg}^{-1}\cdot\text{m}^{-1}$, and vertical walking is $1.8\,\text{ml}\cdot\text{kg}^{-1}\cdot\text{m}^{-1}$.

What is the formula used to calculate power on a cycle ergometer?

$$\text{Power } (\text{kg}\cdot\text{m}\cdot\text{min}^{-1}) = \text{resistance } (\text{kg}) \times \text{flywheel size } (\text{m/rev}) \times \text{cadence } (\text{rev/min})$$

What three components determine the energy cost of cycle ergometry?

1. Unloaded cycling (moving the flywheel itself, including resting expenditure). 2. External resistance (load on the flywheel). 3. Body mass.

What are the typical resting values for RER, $\dot{V}O_2$, and daily metabolic rate?

At rest, RER is approximately $0.80$, $\dot{V}O_2$ is about $0.3\,\text{L}\cdot\text{min}^{-1}$, and metabolic rate is about $2{,}000\,\text{kcal/day}$.

What standardized conditions are required to determine basal metabolic rate (BMR)?

The individual must be in a supine position in a thermoneutral environment following $8\,\text{h}$ of sleep and $12\,\text{h}$ of fasting.

How does resting metabolic rate (RMR) differ from basal metabolic rate (BMR)?

RMR does not require the stringent standardized conditions of BMR, falls within $5\%$ to $10\%$ of BMR, and typically ranges from $1{,}200$ to $2{,}400\,\text{kcal/day}$.

What is the slow component of $\dot{V}O_2$ kinetics during submaximal aerobic exercise?

At high power outputs, $\dot{V}O_2$ continues to increase over time rather than plateauing, driven by the recruitment of less efficient type II muscle fibers.

What is $\dot{V}O_2$ drift?

An upward drift in $\dot{V}O_2$ observed during prolonged exercise at a constant, low power output, potentially caused by ventilatory and hormonal changes.

How does $\dot{V}O_{2\text{max}}$ adapt to training compared to endurance performance?

$\dot{V}O_{2\text{max}}$ typically plateaus after $8$ to $12\,\text{weeks}$ of training, whereas performance continues to improve as the athlete learns to compete at a higher percentage of their $\dot{V}O_{2\text{max}}$.

What are the normalized $\dot{V}O_{2\text{max}}$ values for untrained young men versus women, and what explains the difference?

Untrained young men average $44$ to $50\,\text{ml}\cdot\text{kg}^{-1}\cdot\text{min}^{-1}$, while untrained young women average $38$ to $42\,\text{ml}\cdot\text{kg}^{-1}\cdot\text{min}^{-1}$; the difference is due to women's lower fat-free mass and lower hemoglobin levels.

What physiological restorations occur during excess postexercise $O_2$ consumption (EPOC)?

EPOC replenishes ATP and PCr stores, converts lactate to glycogen, replenishes hemoglobin and myoglobin oxygen stores, and clears $CO_2$.

What is the lactate threshold and what does it indicate?

It is the point at which blood lactate accumulation increases markedly because production exceeds clearance; it reflects the interaction between aerobic and anaerobic systems and is a good predictor of endurance performance.

What four physiological characteristics define successful endurance athletes?

1. High $\dot{V}O_{2\text{max}}$. 2. High lactate threshold (as a percentage of $\dot{V}O_{2\text{max}}$). 3. High economy of effort. 4. High percentage of type I muscle fibers.