exercise vs limber up

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

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

As verbs, limber up is a hyponym of exercise; that is, limber up is a word with a more specific, narrower meaning than exercise:

exercise: do physical exercise
limber up: make one's body limber or suppler by stretching, as if to prepare for strenuous physical activity

Other hyponyms of exercise include loosen up, warm up, train, tumble, strengthen, tone, tone up, press, weight-lift, weightlift.

exercise (noun)	limber up (noun)
the activity of exerting your muscles in various ways to keep fit
a task performed or problem solved in order to develop skill or understanding
systematic training by multiple repetitions
the act of using
an action, often used negatively and without consequences
(usually plural) a ceremony that involves processions and speeches

exercise (verb)	limber up (verb)
do physical exercise	make one's body limber or suppler by stretching, as if to prepare for strenuous physical activity
give a workout to	attach the limber
learn by repetition
put to use
carry out or practice; as of jobs and professions