Aerobic Metabolism and Energy Production Quiz

Aerobic Metabolism

• Aerobic metabolism is a crucial energy-generating process, utilizing oxygen.
• It's essential for various physical activities, like running and cycling, that last longer than a couple of minutes.
• Mitochondria play a vital role in aerobic metabolism, which includes glycolysis, Krebs cycle, and the electron transport chain (ETC).
• Different substrates, like carbohydrates (glucose/glycogen), fats (fatty acids/triglycerides), proteins (amino acids), and lactate, contribute to aerobic energy generation.
• Learning objectives are about defining aerobic metabolism, oxygen's role in it, factors affecting substrate use during exercise (like intensity and duration), oxygen consumption changes, metabolic recovery after exercise, and the physiological adjustments for higher ATP production.

Metabolic Recap

• The ATP-PC system provides energy for the initial 30 seconds of exercise.
• Anaerobic glycolysis is the primary energy source for the first 2-3 minutes after the ATP-PC system is depleted.
• Exercise beyond the initial capacity will increase the contributions of glycolysis.

Glycolysis

• Glycolysis is the initial breakdown of glucose/glycogen to pyruvate.
• This occurs in the sarcoplasm and comprises 10 or 11 steps.
• ATP production is relatively minor in glycolysis.
• Glycolysis can be anaerobic or aerobic. Aerobic is slower than anaerobic.

Glycolysis overview

• Anaerobic glycolysis is fast and doesn't involve oxygen, while aerobic is slower and employs oxygen.
• Only small amounts of ATP are generated during glycolysis, an early stage in aerobic metabolism.

Fat Metabolism

• Fats (triglycerides) are broken down into fatty acids and glycerol via lipase.
• Beta-oxidation is the process where fatty acids are broken down into acetyl CoA in the mitochondria.
• No ATP is produced directly during this initial breakdown.
• Glycerol is converted to glucose or pyruvate, which then enters further metabolic pathways.

Protein metabolism

• Proteins are broken down to amino acids via deamination/transamination in order to enter energy pathways.
• Some amino acids become glucose, while others form acetyl CoA and can enter the Krebs cycle.

Kreb's Cycle

• Occurs in the mitochondrial matrix.
• The cycle starts and ends with oxaloacetate.
• A small amount of ATP is produced (1 ATP per acetyl CoA).
• Important hydrogen carriers (NADH and FADH2) are generated.
• CO2 is released.

Electron Transport Chain

• Occurs in the inner mitochondrial membrane.
• This is the major ATP-generating part of aerobic metabolism.
• Electrons are transferred, generating a proton gradient.
• Oxygen is the final electron acceptor.
• ATP synthase uses the gradient for ATP synthesis.

Lactate Threshold

• The exercise intensity at which blood lactate (La+) exceeds resting concentration.
• When lactate production exceeds clearance, performance is impaired.
• Blood lactate concentration increase, which produces acidity, impairing muscle contraction.
• In trained individuals, the lactate threshold is higher.

Metabolic Recovery After Exercise

• Intramuscular PC stores are resynthesized.
• Intramuscular and blood acidity levels are reduced.
• Elevated heart rate, breathing rate, and metabolic rate are common during recovery, requiring aerobic metabolism to restore body systems.

O2 Deficit

• O2 deficit is the difference between oxygen consumed and the amount required if aerobic metabolism met demands.

Steady-State O2 Consumption

• Steady-state O2 consumption occurs when all energy required is met aerobically.

Excess Post-exercise Oxygen Consumption (EPOC)

• Oxygen taken in above resting levels after exercise has ended.
• Higher exercise intensity usually means a higher EPOC.
• Various metabolic processes during recovery, including the restoration of PCr, metabolizing lactate, and restoring glucose or glycogen contribute to EPOC.

Active vs. Passive Recovery

• Active recovery reduces plasma lactate levels faster and to lower peak levels than passive recovery.

Carbohydrate Availability and Performance

• Reduced carbohydrate stores lead to increased reliance on fat metabolism.
• This can result in a lower rate of energy supply and fatigue.

Carbohydrate Loading

• Consuming additional carbohydrates before prolonged exercise can improve performance in endurance events by maximizing glycogen stores.

Substrate Utilization During Exercise and Rest

• The preferred substrate depends on exercise intensity and duration.
• During low intensity/lasting exercises, fats are primarily used.
• High-intensity or shorter exercises often employ carbohydrates as the main fuel source.

Aerobic Adaptations to Exercise

• Increased mitochondrial density and enzyme activity enhance ATP production and increase the capacity to utilize fats during exercise.
• Higher cardiac output/blood flow/myoglobin faster lactate removal will also play a role in improved performance.
• Increasing intramuscular stores for aerobic and anaerobic use and increasing intramuscular triglycerides improves aerobic metabolism, leading to performance improvements.

Energy Systems Used During Sports

• Different sports utilize different energy systems based on the duration and intensity of the activity.
• Short-duration, high-intensity activities rely on the ATP-PC system and anaerobic glycolysis.
• Activities lasting longer use aerobic metabolism progressively more.

Metabolism: Applications

• Short-duration, high-intensity activities have limited metabolic capacity.
• The sustained racing pace of endurance activities relies on the body's ability to switch to aerobic sources and use fat effectively.

Measuring Aerobic Metabolism

• Calorimetry and spirometry methods are used to measure aerobic metabolism.
• Open circuit spirometry estimates the amount of oxygen consumed. Accurate measurement may be affected by issues during the test.

Oxygen Consumption

• VO2, measured in liters per minute, represents the volume of oxygen consumed, while mL/kg/min reflects a person's body weight.
• Absolute VO2 measure doesn't account for body weight, but the relative (mL/kg/min) measure does, which is usually used in other sports beyond rowing or situations requiring larger measurements

Respiratory Exchange Ratio (RER)

• The RER is the ratio of carbon dioxide produced to oxygen consumed during metabolism.
• RER values (VCO2/VO2) change depending on the substrate the body uses to create energy.
• Lower RER values indicate higher use of fat for energy production, while higher values indicate increased carbohydrate utilization.

RER Estimates

• RER values typically fall between 0.7-1.0, indicating a mixed energy source of both CHO and TG.

Practical Example

• The example presents information about oxygen consumption, carbon dioxide usage, respiratory quotient (RQ), heart rate (HR), and energy expenditure (energy per kcal) during different periods of strenuous activity.

Can RER exceed 1.0?

• RER can exceed 1.0 at higher intensities because the body uses anaerobic pathways and bicarbonate buffering occurs more intensely at greater intensities.

Endurance Event Metabolic Interactions

• Endurance activities employ a significant reliance on aerobic processes to sustain prolonged activities.
• Various energy sources are used for different duration and intensity activities, indicating the body can switch between fuel sources.