I remember when I was a kid I have seen an anime(it was a movie not a series I think). It was some kind of sci-fi. Only scene I remember icludes two main characters - young boy\man and a girl training(sparring?) in some kind of training room. There is also their robot who is curious why they waste energy, and they explain to him that for humans, the more they train(get tired) the more stronger they become. Anybody remembers such movie :-) ?