When it comes to maintaining or sustaining a particular action, we often use the phrase "keep something up". However, there are several synonyms that can be used interchangeably to convey the same meaning. For instance, one could say "continue", which suggests moving forward without interruption or hesitation. Additionally, "maintain" is another suitable synonym, emphasizing the idea of preserving or upholding a particular state or action. Similarly, "sustain" implies the ability to endure or prolong an activity or behavior. Other alternatives include "persevere", highlighting the determination in staying committed, and "prolong", which suggests extending the duration of something. Ultimately, these synonyms all capture the essence of "keep something up" while offering variety in expression.