When we say exercise, I am a fan of the long walk or yoga. Any kind of movement can help unblock your thoughts and foster creative insights. Including the shower after the exercise.
I hate walking the dog on city streets, but I love walking the dog on a nature trail. I don’t need to watch for traffic, or worry about other dogs to distract him or me. So when you consider your exercise, consider how meditative it is. Are you participating in team sports? Great workout, but does that inspire your work? Are you walking with a friend who speaks? Is that helping your process or allowing you to just ruminate over the same problems?
Try a walk alone, try time away. During December, it can make the difference not only in your creativity, but also you sanity!