During forced expiration , actively contracting muscles

Options

A. diaphragm
B. external intercostals
C. abdominal muscles
D. all of these

Answer

**Step-by-Step Solution:**

1. **Understanding Expiration**: Expiration is the process of breathing out. It can be either passive or forced. In normal expiration, the diaphragm and external intercostal muscles relax, allowing air to exit the lungs without the need for active muscle contraction.

2. **Identifying Forced Expiration**: Forced expiration occurs during activities that require a rapid and forceful expulsion of air, such as during heavy exercise or when blowing out candles. This process requires the active contraction of certain muscles.

3. **Muscles Involved in Forced Expiration**:
- The diaphragm and external intercostal muscles are primarily involved in normal expiration and are not actively contracting during forced expiration.
- The abdominal muscles play a crucial role in forced expiration. When they contract, they increase intra-abdominal pressure, which helps push the diaphragm upwards and pull the ribcage downwards and inwards, facilitating the expulsion of air from the lungs.

4. **Conclusion**: Since the question specifically asks about actively contracting muscles during forced expiration, the correct answer is the abdominal muscles.

**Final Answer**: The correct option is the abdominal muscles (Option 3).

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