When someone says they are "in full action," it typically means they are actively engaged in doing something to their fullest capacity. However, there are many other synonyms for this phrase that can be used to express the same idea. Some of these phrases include "in full swing," "going strong," "at peak performance," "operating at maximum capacity," "fully engaged," "hard at work," and "in the zone." Each of these phrases highlights the idea of someone being fully immersed in whatever they are doing, and gives the impression that they are completely focused on their task at hand. Whether you're an athlete, musician, or business professional, being "in full action" is a state of mind that can lead to great success.