Chapter 5: Energy Expenditure

Vocabulary flashcards covering key terms and concepts from Chapter 5: Energy Expenditure.

Direct Calorimetry

Measures energy expenditure by capturing and measuring heat production in a calorimeter; 40% of substrate energy to ATP and 60% to heat; accurate for resting measurements but expensive and impractical for exercise.

Substrate Metabolism Efficiency

The proportion of substrate energy captured as ATP versus lost as heat (about 40% to ATP, 60% as heat in the notes).

Indirect Calorimetry

Estimates total energy expenditure from O2 consumed and CO2 produced; relies on respiratory gas measurements and is most accurate for steady-state oxidative metabolism.

V•O2 (Oxygen Consumption per Minute)

Volume of O2 consumed per minute; rate of O2 usage, calculated as inspired O2 minus expired O2.

V•CO2 (Carbon Dioxide Production per Minute)

Volume of CO2 produced per minute; rate of CO2 production, calculated as expired CO2 minus inspired CO2.

Haldane Transformation

Method to calculate inspired gas volumes from expired gas using constant N2 volumes; enables determination of VI and VE.

Respiratory Exchange Ratio (RER)

Ratio of CO2 produced to O2 consumed (VCO2/VO2); indicates substrate use; ~1.0 for glucose oxidation, ~0.70 for fat oxidation.

RER and Fuel Mixtures (Energy per L O2)

RER correlates with kcal per liter of O2; typical values range from about 4.69 to 5.05 kcal/L O2 depending on fuel mix (lower for fats, higher for carbohydrates).

Isotopic Measurements

Use of isotopes (e.g., 13C, 2H) to trace energy metabolism and CO2 production; easy, accurate, low-risk; suitable for long-term measurements.

Heart Rate Monitoring (HR-based Energy Estimation)

Estimates VO2 from heart rate using regression developed during submaximal exercise; limited by temperature, fitness, and activity type.

Pedometers

Devices that count steps to estimate activity; limited accuracy at slow speeds, location-dependent readings, and needs calibration.

Accelerometers

Devices that detect acceleration to quantify movement and intensity; provide continuous data but may be inaccurate for sedentary or non-aerobic activities.

Self-Report Methods

Activity questionnaires and diaries; subject to bias and lower accuracy.

VO2max

Maximum rate of O2 uptake during intense exercise; best single measure of aerobic fitness; plateaus after 8–12 weeks of training.

VO2max Units

Measured in liters per minute (L/min) or milliliters per kilogram per minute (ml/kg/min).

EPOC (Excess Postexercise O2 Consumption)

Increased O2 consumption after exercise to restore ATP/PCr stores, oxidize lactate, and clear CO2.

Lactate Threshold

The exercise intensity at which blood lactate begins to accumulate rapidly; expressed as a percentage of VO2max; higher threshold indicates better endurance.

Economy of Effort

Improvement in energy efficiency with practice; lower energy cost at a given pace; varies with distance and activity type.

Endurance Athlete Profile

High VO2max, high lactate threshold, high economy of effort, and a high proportion of Type I muscle fibers.

BMR (Basal Metabolic Rate)

Minimum energy expenditure at rest under strict conditions (supine, thermoneutral, post-absorptive); related to fat-free mass.

RMR (Resting Metabolic Rate)

Energy expenditure at rest similar to BMR but measured under less stringent conditions; typically 1,200–2,400 kcal/day.

BMR vs RMR

BMR requires strict testing conditions; RMR is easier to measure and often slightly higher under typical daily conditions.

Resting Energy Expenditure at Rest

At rest, VO2 ≈ 0.3 L/min and RER ≈ 0.80; total daily metabolic rate about 2,000 kcal/day.

Submaximal Aerobic Exercise and O2 Kinetics

VO2 increases with exercise intensity; slow component due to recruitment of less efficient type II fibers and VO2 drift.

VO2 Drift

Gradual rise in VO2 during sustained submaximal exercise at a constant workload.

VO2max Plateau

Point where VO2 no longer increases with increased intensity; used to define VO2max.

Anaerobic Energy Expenditure

Energy produced by anaerobic pathways; estimated via EPOC and lactate threshold.

Energy Cost of Various Activities

Energy cost varies by activity type and intensity; calculated from VO2 and expressed as kcal/min; excludes anaerobic contributions and EPOC.