The most effective strategy for reducing stress in the context provided would be to imagine you are doing your gymnastics routine by practicing it in your head over and over before the big competition. This mental rehearsal can help build confidence, improve focus, and reduce anxiety by familiarizing yourself with the routine, making it feel more manageable and less daunting when you actually perform it.
In contrast, the other strategies—playing video games before chores, sacrificing sleep for studying, and avoiding rehearsal until the last moment—can contribute to increased stress and a sense of being overwhelmed.