…………..muscle fibres are involved in rapid contraction for short duration while ………….in slow contraction for long period.

Explanation

To answer the question, we need to identify the types of muscle fibers based on their contraction characteristics.

1. **Identify the first type of muscle fiber**: The question states that the first type of muscle fiber is involved in rapid contraction for a short duration. This type of muscle fiber is known as **white muscle fibers**.

- **Explanation**: White muscle fibers, also known as fast-twitch fibers, have fewer mitochondria and less myoglobin. They are designed for quick bursts of energy and can contract rapidly but fatigue quickly.

2. **Identify the second type of muscle fiber**: The second part of the question refers to muscle fibers that contract slowly but can sustain this contraction for a longer period. This type of muscle fiber is known as **red muscle fibers**.

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