When a skeletal muscles shortens during contraction, which of these statements is false?

Options

A. The I-bands shorten
B. The A-bands shorten
C. The H-bands shorten
D. The sarcomeres shorten

Answer

To determine which statement about skeletal muscle contraction is false, let's analyze each statement step by step.

1. **Understanding Muscle Structure**:
- Skeletal muscles are made up of units called sarcomeres, which contain thick (myosin) and thin (actin) filaments.
- The **A band** is the region that contains both thick and thin filaments and remains constant in length during contraction.
- The **I band** consists solely of thin filaments and shortens during contraction.
- The **H band** is the part of the A band that contains only thick filaments and also shortens during contraction.

2. **Analyzing Each Statement**:
- **Statement 1**: The I band shortens.
- This statement is true because during muscle contraction, the I band decreases in length as the actin filaments slide over the myosin filaments.
- **Statement 2**: The A band shortens.
- This statement is false. The A band does not change in length during contraction; it remains the same.
- **Statement 3**: The H band shortens.
- This statement is true because the H band decreases in length as the actin filaments slide over the myosin filaments.
- **Statement 4**: The sarcomere shortens.
- This statement is true because the overall length of the sarcomere decreases during contraction as the I band and H band shorten.

3. **Conclusion**:
- The false statement among the options is that the A band shortens. Therefore, the correct answer is that the A band remains the same during contraction.

### Final Answer:
The false statement is: **The A band shortens.**