Just like working out can keep your body in good shape, stretching your brain can keep it razor sharp. Doing them together has an added benefit. Scientists say that working the body and the mind at the same time revitalizes our brain cells. So, fill-out a crossword puzzle while riding a stationary bike, or listen to language lessons on your iPod while on the treadmill. If you don’t like multi-tasking, do a crossword right after the gym, when you’re energized. It'll have the same benefits.