Fatigue is mostly associated with

Options

A. repeated stimulation of muscles
B. excessive work load on muscles
C. anaerobic respiration in muscles
D. all of these

Answer

To solve the question "Fatigue is mostly associated with," we will analyze each option provided and determine which one is the most accurate in relation to muscle fatigue.

### Step-by-Step Solution:

1. **Understanding Fatigue**:
- Fatigue in muscles is a condition where muscles lose their ability to generate force or power. It is often associated with prolonged physical activity.

2. **Analyzing the Options**:
- **Option 1: Repeated stimulation of muscle**:
- While repeated stimulation can lead to fatigue, it is not the primary cause. Muscles can still function under repeated stimulation if oxygen is available.
- **Option 2: Excessive workload on muscle**:
- Excessive workload can contribute to fatigue, but it is not the main factor. If the workload is manageable and aerobic respiration occurs, fatigue may not be experienced.
- **Option 3: Anaerobic respiration in muscle**:
- This is a significant factor in muscle fatigue. During intense exercise, when oxygen levels are low, muscles rely on anaerobic respiration, leading to the production of lactic acid. The accumulation of lactic acid causes muscle fatigue.
- **Option 4: All of these**:
- While all the factors mentioned can contribute to fatigue, the most direct and significant cause is anaerobic respiration.

3. **Conclusion**:
- After analyzing all the options, **Option 3: Anaerobic respiration in muscle** is the correct answer. It is the primary mechanism leading to the accumulation of lactic acid, which is a major contributor to muscle fatigue.

### Final Answer:
**Option 3: Anaerobic respiration in muscle.**

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