They're opposites, so they're antonyms.
forward
bent backward
The usual antonym is backward. Others with regard to direction are reverse or rearward.
up - down hot - cold girl - boy yes - no in - out behave - misbehave run - walk agree - disagree balance - imbalance mother - father brother - sister old - young near - far inside - outside. nice mean pretty ugly
There is no antonym, but there are many synonyms.
The antonym for forward is backward, but the opposite direction can be reverse or rearward.
You may be confusing foreword with the soundalike forward. As an adverb it refers to a direction towards the front of something (facing forward); its antonym would be backward.
They are synonyms, not antonyms.
They are synonyms.
bent backward
They are synonyms.
***** Opposite.