They do that so we can understand. So instead of two ninja's fighting and one pulls a kick a$$/incredible Technique outta nowhere and one dies or hurts the other drastically, and nothing is said, how would we know? But sometimes a sweet tech. is used and nothing is said about it, only b/c it is usually a main, known, or new character's move but is reveled later so we may grasp the idea so we can make sense on how awesome, lame, or cheap the move/ tech. is. I could go on and on about it but need I really? -Long Story Short- this is B/c it's for us (the reader) to understand what's going on and not to be left out in the dark on things, too much. And w/o this manga would be dead, no one but the Author and Artist would know what's going on, unless they make it a plain and clear manga story-line, and that's just no good. P.S The way they run makes it more appealing to the reader/viewer if the hands are behind them, it wouldn't be as appealing. And if your so obsessed about the "non efficient" way they run, don't you think how impossible it is how they do, well EVERYTHING ELSE?!? They are NINJA'S who cares how they run? They can do such crazy inhuman things! Why pay ANY attention to how they run, or put too much thought into it. Sorry that's just my opinion(s).