Well a few years ago a experiment was held: There was 60 people, 30 of which where told to work out intensely 60 mins everyday, the other thirthy where to practise visualizing working out for 30 mins each day. By the end of the period the workout people had gained over 40% extra muscle mass, while the other 30 gained an amazing 20% extra muscle mass just by thinking. The exact reason for the outcome of the experiment has never become clear I believe, but it does show that it could be possible to physically effect your body. So in a way training with fifty tonne weights in your lucid dream may actually have an effect on your real physical body