keep up vs sustain

keep up and sustain both are verbs.

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

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

Other synonyms of keep up include prolong.

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