What is common between the muscle fibers of extensor of human back and those of flight muscles of the birds which remain in flight for long periods of time ?
a. They are thinner , red colored
b, they are thicker and light colored .
c. they have abundant mitochondria .
d. they have well developed sarcoplasmic reticulum
e. they show rate of contractions for longer periods
f, They show fast stenous activity
g. They do not get fatigued early .
h. They get fatigued quickly .

Options

A. a,c,e,g ,are common
B. b,d,f,h are common
C. All features are common at different times
D. a,c,f,g are common

Answer

To determine what is common between the muscle fibers of the extensor of the human back and those of the flight muscles of birds, we can analyze the characteristics of these muscle fibers step by step.

### Step-by-Step Solution:

1. **Identify Muscle Fiber Types**:
- The extensor muscles of the human back and the flight muscles of birds are primarily composed of red muscle fibers. These fibers are known for their endurance and ability to sustain prolonged activity.

2. **Color of Muscle Fibers**:
- Red muscle fibers are thinner and have a higher myoglobin content, which gives them their red color. This is important for oxygen storage and utilization during aerobic respiration.

3. **Mitochondrial Abundance**:
- Red muscle fibers have abundant mitochondria, which are essential for aerobic respiration. This allows these muscles to generate energy efficiently over long periods without fatigue.

4. **Sarcoplasmic Reticulum Development**:
- The sarcoplasmic reticulum is less developed in red muscle fibers compared to white muscle fibers. Therefore, this characteristic does not apply to both muscle types.

5. **Rate of Contraction**:
- Red muscle fibers contract slowly but can sustain contractions for longer periods. This is crucial for activities like maintaining posture in humans and sustained flight in birds.

6. **Fatigue Resistance**:
- Both muscle types do not get fatigued easily due to their high mitochondrial content. This allows them to perform activities for extended durations without tiring quickly.

7. **Fast Strenuous Activity**:
- Fast and strenuous activities are characteristic of white muscle fibers, not red muscle fibers. Thus, this option is not applicable to the comparison.

### Conclusion:
Based on the analysis, the common characteristics between the muscle fibers of the extensor of the human back and those of the flight muscles of birds are:
- They are red in color (Option A).
- They have abundant mitochondria (Option C).
- They can sustain contractions for longer periods (Option E).
- They do not get fatigued early (Option G).

Thus, the correct answer is that options A, C, E, and G are common between the two muscle types.