Which of the following correctly characterises a "fast-oxidative " type of skeletal muscle fibre?

Options

A. Few mitochondria and high glycogen content
B. Low myosin AT Pase rate and few surrounding capillaries
C. Low glycolytic enzyme activity and intermediate contraction velocity
D. High myoglobin content and intermediate glycolytic enzyme activity

Explanation

To determine which option correctly characterizes a "fast-oxidative" type of skeletal muscle fiber, we can analyze the characteristics of these fibers step by step.

### Step-by-Step Solution:

1. **Understanding Fast-Oxidative Fibers**:
- Fast-oxidative fibers, also known as fast oxidative glycolytic (FOG) fibers, are a type of skeletal muscle fiber that can contract rapidly and resist fatigue. They are designed for activities that require both strength and endurance.

2. **Key Characteristics**:
- These fibers have a high content of myoglobin, which is a protein that binds oxygen and facilitates aerobic respiration.
- They possess a moderate number of mitochondria, which are essential for aerobic energy production.
- Fast-oxidative fibers also have intermediate levels of glycolytic enzyme activity, allowing them to generate energy through both aerobic and anaerobic pathways.

3. **Evaluating the Options**:
- **Option 1**: Few mitochondria and high glycogen content - This does not characterize fast-oxidative fibers, as they have more mitochondria.
- **Option 2**: Low myosin ATPase rate and few surrounding capillaries - This is incorrect because fast-oxidative fibers have a higher myosin ATPase rate and more capillaries for oxygen delivery.
- **Option 3**: Low glycolytic enzyme activity and intermediate contraction velocity - This is not accurate, as fast-oxidative fibers have intermediate glycolytic enzyme activity.
- **Option 4**: High myoglobin content and intermediate glycolytic enzyme activity - This correctly describes fast-oxidative fibers.

4. **Conclusion**:
- Based on the analysis, the correct characterization of fast-oxidative skeletal muscle fibers is given in **Option 4: high myoglobin content and intermediate glycolytic enzyme activity**.

### Final Answer:
**The correct option is 4: High myoglobin content and intermediate glycolytic enzyme activity.**

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