The muscles which are immune to fatigue are _____

Explanation

**Step-by-Step Solution:**

1. **Understanding Fatigue in Muscles:**
- Fatigue refers to the state of being tired or exhausted, particularly in the context of muscle activity. Some muscles can become fatigued after prolonged use, while others do not.

2. **Types of Muscles:**
- There are three main types of muscles in the human body: skeletal muscles, smooth muscles, and cardiac muscles.
- Skeletal muscles are voluntary and can fatigue with extensive use.
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