The phrase utmost extents refers to the highest level of effort, commitment, or intensity. There are a number of synonyms that can be used to convey a similar meaning. For example, one could say utmost limits, absolute maximum, total magnitude, extreme boundaries, or ultimate threshold. Other options might include peak performance, total dedication, ultimate exertion, or complete devotion. All of these phrases indicate a level of dedication or commitment that is beyond what is considered normal or expected, and suggest a willingness to go above and beyond in pursuit of a goal or objective. Overall, these synonyms help to convey a sense of focus, determination, and intensity.