Meaning of “keep sth up” - Learner’s Dictionary

keep sth up

phrasal verb with keep uk us /kiːp/ verb (past tense and past participle kept)

B1 to not allow something that is at a high level to fall to a lower level:

Make sure you eat properly - you've got to keep your strength up.

(Definition of “keep sth up phrasal verb, verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)