it depends on how much you train for and the intensity of it.if you feel knackered after it-and then go straight to the dojo -you re doing too much. But if its only light exercise which will help to warm up the muscles, and you do some stretching after it, it should help prepare your body for training. Sounds like you are doing a bit too much beforehand though. And make sure that you had something to eat bout an hour and a half before training as fuel for your body. If you ve trained- gone home , not eaten, then go to training again, your fuel tank will be empty, and your body will suffer.