sustain vs keep up

sustain and keep up both are verbs.

Word	Noun	Adjective	Verb	Adverb
sustain	No	No	Yes	No
keep up	No	No	Yes	No

As verbs, sustain and keep up are synonyms defined as:

Other synonyms of sustain include prolong.

sustain (verb)	keep up (verb)
undergo (as of injuries and illnesses)	prevent from going to bed at night
establish or strengthen as with new evidence or facts	keep informed
admit as valid	maintain a required pace or level
supply with necessities and support	keep in safety and protect from harm, decay, loss, or destruction
provide with nourishment	lengthen or extend in duration or space
be the physical support of; carry the weight of
lengthen or extend in duration or space