Which of the following biological processes explains why human muscles often feel sore or "cramped" after a sudden, intense bout…

Question

Which of the following biological processes explains why human muscles often feel sore or "cramped" after a sudden, intense bout of physical exercise?

1. A. Accumulation of Ethyl Alcohol
2. B. Excessive release of Carbon Dioxide
3. C. Depletion of Vitamin C
4. D. Accumulation of Lactic Acid (Correct answer)

Correct Answer

Option D — Accumulation of Lactic Acid

Detailed Solution & Explanation

The correct answer is Accumulation of Lactic Acid.

Key Points

• During intense exercise the muscles' oxygen supply falls short of demand, so they switch to anaerobic respiration.
• Glucose is then broken down incompletely, producing lactic acid rather than carbon dioxide and water.
• Lactic acid building up in the muscle tissue produces the familiar soreness, fatigue and cramping.

Additional Information

• Aerobic respiration: glucose + oxygen → carbon dioxide + water + ~38 ATP. Anaerobic respiration in muscle: glucose → lactic acid + only 2 ATP — far less efficient, which is why intense effort cannot be sustained.
• In yeast, anaerobic respiration instead yields ethyl alcohol and carbon dioxide, the basis of fermentation — which is why option A is a plausible-sounding trap drawn from a different organism.
• The oxygen debt incurred is repaid afterwards through continued heavy breathing, which clears the accumulated lactic acid via the liver.
• Respiration occurs in the mitochondria, the cell's powerhouse, and the energy currency released is ATP.