Muscle fatigue in the body of an athlete is due to__________

Step 1: Analyze the question The question asks what causes muscle fatigue in an athlete. This ties to respiration in muscles during strenuous exercise.

Step 2: The concept During vigorous exercise, muscles need energy faster than the blood can supply oxygen. The muscle cells then respire anaerobically (without enough oxygen):

Glucose → Lactic acid + a small amount of energy (2 ATP)

Lactic acid is not removed as fast as it is made, so it builds up in the muscle tissue. This causes the pain, cramps, and tiredness we call muscle fatigue. After exercise, the athlete breathes heavily to take in extra oxygen and pay back the oxygen debt, which breaks down the lactic acid in the liver.

Step 3: Evaluate the options

• A. Low pH: Lactic acid does lower the pH, but this is a result of the acid building up, not the primary cause. It is a tempting distractor.
• B. High oxygen content: Wrong. Fatigue happens when oxygen is low, not high.
• C. Accumulation of lactic acid: Correct. This is the direct cause of muscle fatigue.
• D. Accumulation of carbonic acid: Carbonic acid comes from CO₂ dissolving in water. It is not the cause of muscle fatigue.

Step 4: Answer The correct option is C. accumulation of lactic acid.

Exam tip: Remember the chain: Strenuous exercise → oxygen shortage → anaerobic respiration → lactic acid builds up → fatigue → oxygen debt repaid by heavy breathing. In WASSCE, "muscle fatigue" or "cramp" almost always points to lactic acid. Fermentation in yeast gives ethanol and CO₂, while in muscles it gives lactic acid.