Lying prone on a bench

[ROBINDESBOIS]

it means lying flat (http://www.macmillandictionary.com/search/british/?q=flat) with (http://www.macmillandictionary.com/search/british/?q=with) the (http://www.macmillandictionary.com/search/british/?q=the) front (http://www.macmillandictionary.com/search/british/?q=front) of (http://www.macmillandictionary.com/search/british/?q=of) your (http://www.macmillandictionary.com/search/british/?q=your) body (http://www.macmillandictionary.com/search/british/?q=body) facing (http://www.macmillandictionary.com/search/british/?q=facing) downwards (http://www.macmillandictionary.com/search/british/?q=downwards).
How can we say facing upwards.?

[Perikles]

How about: Lying on your back ? :rolleyes:

[hermit]

The opposite of 'prone' is 'supine'.

[Perikles]

The opposite of 'prone' is 'supine'.That's true, but not many people use the word.

[Tomisimo]

Also "lying face up on the beach".

[hermit]

that's true, 'supine' is a little-known word outside of anatomical usage
such as 'pronation/supination'.

[irmamar]

Prono / supino in Spanish, too. Very common word in gymnastics (I still remember my gymnastics teacher :eek: ) :D

[chileno]

Doctors use those terms too.

En Chile con decir "boca arriba" or "boca abajo", es suficiente.