Mechanisms of ATP Production and Their Implications

• Aerobic catabolism consists of four major sets of reactions
• BOX 8.1 Reactive Oxygen Species (ROS)
• O₂ deficiency poses two biochemical challenges: Impaired ATP synthesis and potential redox imbalance
• Certain tissues possess anaerobic catabolic pathways that synthesize ATP
• Anaerobic glycolysis is the principal anaerobic catabolic pathway of vertebrates
• What happens to catabolic end products?
• The functional roles of ATP-producing mechanisms depend on whether they operate in steady state or nonsteady state
• Phosphagens provide an additional mechanism of ATP production without O₂
• Internal O₂ stores may be used to make ATP

Comparative Properties of Mechanisms of ATP Production

• Question 1: What is each mechanism’s total possible ATP yield per episode of use?
• Question 2: How rapidly can ATP production be accelerated?
• Question 3: What is each mechanism’s peak rate of ATP production (peak power)?
• Question 4: How rapidly can each mechanism be reinitialized?
• BOX 8.2 Genetic Engineering as a Tool to Test Hypotheses of Muscle Function and Fatigue
• Conclusion: All mechanisms have pros and cons

Two Themes in Exercise Physiology: Fatigue and Muscle Fiber Types

• Fatigue has many, context-dependent causes
• The muscle fibers in the muscles used for locomotion are heterogeneous in functional properties

The Interplay of Aerobic and Anaerobic Catabolism during Exercise

• Metabolic transitions occur at the start and end of vertebrate exercise
• The ATP source for all-out exercise varies in a regular manner with exercise duration
• Related species and individuals within one species are often poised very differently for use of aerobic and anaerobic catabolism

Responses to Impaired O₂ Influx from the Environment

• Air-breathing vertebrates during diving: Preserving the brain presents special challenges
• Animals faced with reduced O₂ availability in their usual environments may show conformity or regulation of aerobic ATP synthesis
• BOX 8.3 Peak O₂ Consumption and Physical Performance at High Altitudes in Mountaineers Breathing Ambient Air
• Water-breathing anaerobes: Some aquatic animals are capable of protracted life in water devoid of O₂