[SSJKarma]

simple PHYSICS of your body !

your pushing your muscles to their extend agiaknst something they cannot move, so what they do is simply continu to grow until you body ackoledge the fact they the arms do not need that effort anymore, so for the next 30 seconds or so, the arms muscles still expand for th eeffort that was given, so your arms are still trying to push those things, so basically since there is nothing, your arms are pushing air which you seems your arms are lifting on their own, but after a few seconds it goes back to normal and your muscles will go their original form.

anyway... not an expert at body complexity, but that's something like that !

you can do with only one arm if you want to, just got to a wall, push it with your arm. do that for about 30 seconds then get off the wall a few feet, the same thing will happen !

well its normal its the same thing but with only one arm. its gonna be more evident tho !