According to sliding filament theory of muscle contraction, the filament that move to shorten a muscle are

Options

A. Myosin
B. Actin
C. Collagen
D. Creating phosphate

Answer

**Step-by-Step Solution:**

1. **Understanding the Sliding Filament Theory**: The sliding filament theory explains how muscles contract at the molecular level. It involves two main types of filaments: actin and myosin.

2. **Role of Myosin**: According to the theory, myosin filaments have heads that bind to actin filaments. This binding is the first step in muscle contraction.

3. **Configuration Change**: Once myosin binds to actin, it undergoes a change in configuration. This change is crucial as it leads to the next step in the contraction process.

4. **Stroke Movement**: The altered myosin heads then perform a stroke movement. This action pulls the actin filaments toward the center of the sarcomere (the basic unit of muscle contraction).

5. **Sliding of Actin**: As myosin pulls on the actin filaments, the actin slides over the myosin filaments. This sliding action is what causes the muscle to shorten during contraction.

6. **Conclusion**: Therefore, the filament that moves to shorten the muscle during contraction is the actin filament.

**Final Answer**: The filament that moves to shorten a muscle according to the sliding filament theory is **actin**.

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