Which chemical accumulates in a fatigued muslce?

Explanation

**Step-by-Step Solution:**

1. **Understanding Muscle Fatigue**: Muscle fatigue occurs after prolonged physical activity. When muscles are overworked, they become tired and less effective in performing their functions.

2. **Anaerobic Conditions**: During intense exercise, the demand for energy in the muscles exceeds the supply of oxygen. This leads to anaerobic conditions, where the muscles cannot rely on aerobic respiration.

3. **Formation of Lactic Acid**: Under anaerobic conditions, glucose is broken down to produce energy, resulting in the formation of lactic acid as a byproduct.

...