We teach the children that martial arts practice is not merely a physical activity. Minds are strengthened through memorization, focusing on a specific task, language building and concentration games.
The same holds true for adults. We need that mental stimulation. It keeps us sharper, clearer and ready for the next challenge.
What to do? Read. Try something new. Take a class. Join/start a discussion group. Write. Find your instrument and practice. Work the puzzle pages: Sudoku, crosswords, math, optical, and language. And then for good measure read some more.