limber vs limber up

limber is a noun but limber up is not a noun.

Word	Noun	Adjective	Verb	Adverb
limber	Yes	Yes	Yes	No
limber up	No	No	Yes	No

As verbs, limber and limber up are synonyms defined as:

limber (noun)	limber up (noun)
a two-wheeled horse-drawn vehicle used to pull a field gun or caisson

limber (adjective)	limber up (adjective)
(used of persons' bodies) capable of moving or bending freely
(used of e.g. personality traits) readily adaptable
(used of artifacts) easily bent

limber (verb)	limber up (verb)
cause to become limber	make one's body limber or suppler by stretching, as if to prepare for strenuous physical activity
attach the limber	attach the limber