The most effective strategy in reducing the amount of stress your body experiences would likely be option A: "Imagine you are doing your gymnastic routine by practicing it in your head over and over before the big competition."
This approach utilizes mental rehearsal, which is a well-documented technique that can improve performance and reduce anxiety. Visualizing yourself performing successfully can boost your confidence, enhance your focus, and help you feel more prepared, all of which can significantly decrease stress levels associated with competitions or performances.
In contrast, the other options (B, C, and D) could lead to additional stress due to procrastination, lack of rest, or inadequate preparation.