During sternous exercise or physical work, the demand for oxygen increase several fold so that it does not diffuse into skekletal muscle fibres at the rates required by them.

Explanation

### Step-by-Step Solution:

1. **Understanding the Context**: During strenuous exercise or physical work, the body requires more oxygen to meet the increased energy demands of the skeletal muscles.

**Hint**: Think about what happens to your body when you exercise. What do your muscles need more of?

2. **Increased Demand for Oxygen**: As the intensity of the exercise increases, the demand for oxygen in the skeletal muscles rises significantly. This is because muscles require oxygen to produce energy through aerobic respiration.

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