specific exercises ( abs) or large volume of work ( tempo) are both work and will make a difference in keeping you lean or getting lean but I dont think anything works quite as well as tempo especially for woman. IMO diet plays a much larger role in your ability to train consistently, your ability to recover and both of these factors will effect overall how lean you will become. Sleep as mentioned is critical ( and all things regenerative) and most people don’t get enough sleep or the quality of the sleep is not consistent.