After vigorous exercise fatigue is caused due to accumulation of which substance?

Options

A. 1.Carbon dioxide
B. 2.Alcohol
C. 3.Lactic acid
D. 4.Water

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the substance that accumulates in the body after vigorous exercise and causes fatigue.

2. **Identifying the Process**: During vigorous exercise, the body requires energy. When the energy demand exceeds the oxygen supply, the body resorts to anaerobic respiration.

3. **Anaerobic Respiration**: In anaerobic respiration, glucose is broken down without oxygen, leading to the production of lactic acid as a byproduct.

4. **Accumulation of Lactic Acid**: As exercise continues, lactic acid accumulates in the muscles. This accumulation is linked to muscle fatigue and cramps.

5. **Conclusion**: Therefore, the substance that causes fatigue after vigorous exercise is lactic acid.

**Final Answer**: Lactic acid.

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