Question

How does the diaphragm help in breathing

Answer 1

Diaphram helps in breathing as when we breathe in, or inhale, our diaphragm contracts (tightens) and moves downward. This increases the space in our chest cavity, into which your lungs expand. 
Similarly as we exhale our diaphragm expands and moves upward. This deceases the space in our chest cavity, into which our lungs contract
tell me if it is helpful 

Answer 2

↪️ diaphragm increase the volume of thoracic cavity during inspiration and decrease the volume of thoracic during expiration.

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I hope it's help you.