The off season is a great time to back off your interval intensity a bit, rest your body and mind, and stay away from training styles that are prone to wearing you down. But, it is also a perfect time to send it! Run some time trials, crank on the last few miles of the long run, jump in some random races! When done appropriately, and in moderation, this can keep your off season stimulating and it can even make you a better racer next season.