Energy Expenditure
Page 1: Objectives
Define the term oxygen deficit: Refers to the difference between the oxygen uptake by muscles and the oxygen demand during physical activity.
Identify primary bioenergetic pathways: Identify how ATP is supplied during different types of exercise.
List factors contributing to oxygen debt (EPOC): Factors that maintain elevated oxygen consumption post-exercise.
Page 2: Key Questions
ATP Supply:
Primary bioenergetic systems based on:
a) Duration: Low- to moderate-intensity exercise.
b) Intensity: High-intensity, brief bouts of exercise.
Nutrient/Fuel Sources:
a) During low- to moderate-intensity: Primarily fats.
b) During high-intensity, brief bursts: Primarily carbohydrates.
Page 3: Energy Expenditure
Total Energy Expenditure Equals:
Energy cost to maintain homeostasis in the body.
Energy required for daily physical activities.
Page 4: Quantifying Energy Expenditure
Calorimetry: Measurement of metabolism through heat released from the body.
Metabolism: Combination of all chemical reactions necessary for survival, with heat as a byproduct that is utilized to assess metabolic efficiency.
Page 5: Calorimetry Techniques
Measurement Types:
Direct Calorimetry: Measures heat dissipated directly from the body.
Indirect Calorimetry: Analyzes expired gases (O2 and CO2) to estimate energy expenditure.
Page 6: Direct Calorimetry Details
Gold Standard: Estimating calories burned.
Bomb Calorimeter: Measures heat from combustion of food to establish caloric content.
Definition of a Calorie: Energy to raise 1kg (1L) of water by 1°C.
Modification of bomb calorimeter for human activity measurement.
Page 7: Indirect Calorimetry Specifics
Utility: Best for exercise physiology.
Oxygen Consumption (V̇O2): Difference between inspired and expired O2 represents oxygen consumption rate.
Haldane Transformation: Mathematical method for estimating O2 and CO2 volumes not directly measured.
Gaseous Composition: O2 (20.93%), CO2 (0.03%), and other inert gases (79.02%).
Page 8: Non-calorimetric Techniques
Prediction Methods for Energy Expenditure:
Objective: Instruments like pedometers & heart rate monitors.
Subjective: Self-reported methods like questionnaires & RPE scales (Rate of Perceived Exertion).
Page 9: Oxygen Consumption in Exercise Energy Expenditure
V̇O2 Measurement: Total oxygen consumed indicates cardiovascular capacity and muscle oxygen extraction ability.
Maximal Oxygen Uptake (V̇O2max): Indicates maximal oxygen utilization during exhaustive exercise.
Implication: Higher V̇O2max correlates with enhanced capacity for physical exertion.
Page 10: Absolute V̇O2
Definition: Total oxygen consumption (in L or mL) independent of body weight.
Consumption Efficiency: 1L of O2 yields approximately 5 kcal.
Practical Example: Calculating energy expenditure based on V̇O2 observed during exercise.
Page 11: Relative V̇O2
Conversion Process: Absolute V̇O2 to relative V̇O2 requires body weight adjustment.
Example Calculation: Converting absolute V̇O2 to mL/kg/min for precise evaluations.
Page 12: Advanced Conversion Techniques
Conversions: From L/min to mL/min and relating to body weight for accurate MET values.
Page 13: Respiratory Exchange Ratio (RER)
Concept: Measures metabolic fuel usage based on CO2 produced vs O2 consumed.
Calculation: RER = V̇CO2 ÷ V̇O2.
Page 14: RER Specifics for Fuel Types
Carbohydrates: RER = 1.0, reflective of maximal carbohydrate metabolism.
Fats: RER ranges close to 0.69, indicative of fat burning as the primary energy source.
Typical RER: Average resting RER between 0.78 and 0.84.
Page 15: O2 Deficit and EPOC
O2 Deficit: Occurs when muscle oxygen uptake cannot meet oxygen demand during exertion.
EPOC: Excess post-exercise oxygen consumption aiding recovery to homeostasis, divided into rapid and slow phases:
Rapid Phase: Lasts 30-60 minutes; involves phosphagen resynthesis, lactate removal, and oxygen reloading.
Slow Phase: Can last up to 48 hours; involves thermoregulation and increased metabolism for recovery tasks.
Page 16: Understanding O2 Deficit
Oxygen Demand: New demands (1.5 L/min) arise, oxygen delivery takes 1-4 minutes, utilizing PCr and glycolysis until aerobic metabolism resumes.
Page 17: Post-Exercise VO2 Dynamics
EPOC Characteristics: Oxygen uptake remains elevated post-exercise; influenced by exercise intensity and duration.
Graph Trend: Displays rapid decline towards resting VO2 after exercise effort.
Page 18: Comparison of Physical Conditioning
Trained vs Untrained: Trained individuals exhibit greater oxygen transport efficiency, resulting in reduced lactic acid production and lower oxygen deficit.
Page 19: Lactate Threshold (LT)
Definition: Point where blood lactate rises systematically; occurs at lower VO2 max in untrained individuals compared to trained counterparts.
Page 20: Issues with Lactic Acid
Impact of H+ Ions: Excess H+ from lactic acid leads to pain and performance degradation by affecting ATP production and muscle contraction efficiency.