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Breathing and ventilation

Diaphragm

The large sheet of muscle under the lungs that does most of the work of breathing in.

What it means

It sits across the base of the chest and flattens downward to pull air in. Because it does most of the work, weakness there is felt sooner than weakness in the other breathing muscles, and is felt soonest when lying flat.

Why you might hear it

  • It explains why lying flat is harder than sitting up.
  • Breathing tests are largely a way of measuring how it is doing.

Where Compass goes into this

About this explanation

These are plain explanations of words you may come across, not advice about your own situation. Where a word matters to a decision, the question pages go into it properly, and your own team is the place to take it.