Lactic Acid System (Anaerobic Glycolysis) – Lecture Notes

Source of Fuel

• \text{Glucose} (rapidly supplied by breakdown of muscle/liver \text{glycogen})

Activation & Operational Window

• Begins contributing after \approx 5\,\text{s} of maximal work
• Reaches full capacity at \approx 10\,\text{s} (when ATP-PC stores are depleted)
• Predominant for continuous maximal efforts lasting 10\text{–}75\,\text{s}
• At sub-maximal intensities ( >85\% max ), can extend to \approx 3\,\text{min}

ATP Yield & Production Rate

• Rapid but slower than ATP-PC due to more chemical steps
• Net resynthesis: 2\,\text{ATP} per glucose molecule

Fatigue Mechanism

• Inadequate oxygen prevents pyruvate entry into aerobic pathways
• Hydrogen ion accumulation lowers intramuscular \text{pH} (acidosis) ➞ inhibited cross-bridge cycling & force; perceived as fatigue

By-Products

• \text{Lactate} (pyruvate + \text{H}^+)
• Accumulated \text{H}^+ ions (cause of acidosis)

Recovery Requirements

• Active recovery maintains blood flow to aid \text{lactate} clearance
• Re-entry of \text{lactate} into blood ➞ liver (Cori cycle) ➞ reconverted to \text{glycogen}
• Repeated high-intensity efforts possible after 2\text{–}5\,\text{min} rest
• Complete lactate removal: 30\,\text{min}\text{ – }2\,\text{h}

Key Takeaways

• Provides a fast, short-term ATP supply once ATP-PC is exhausted
• Limited by acidosis, not fuel availability
• Essential for maximal efforts beyond \approx 10\,\text{s} but under \approx 75\,\text{s}
• Strategic active recovery accelerates system reset for subsequent bouts