As far as I am aware, it can all depend on at what point your testes descended fom inside your body. In some (I dont know the numbers in either case) they are already descended at birth, and in others they descend naturally in the first few years of life, some may be a bit later than that!
As a consequence of "late" descension the canal that the testes travelled down does not block itself off as much as in guys who were fully descended at birth thus allowing the testes to have the ability to either suck up or be pushed up inside the body.
As the testes are designed to be capable of temperature control, and physical protection the body automatically lifts and descends the testes accordingly. One extreme is loose and low, an other is right inside the body.
I am speaking as a person whose testes descended when I was about 5 ish, and in hot weather they will hang loose and low and in cold weather and when having sex they become sucked up towards the body, sometimes getting sucked up right inside.
Most guys will know what their bodies do in their own cases, and it is on boards like this that we exchange our own "norms" for comparison.
It's very normal for a man's testes to draw up when close to orgasm. I have yet to meet a man that this doesn't happen to. I have always joked that they are lining up for firing. My husband actually tries to last longer by forcing them back down.
the martial arts thing is only for a special group of a special kind of kung fu. lol i am a martial artist, its not all of us. but yeah theballs only go in my body if ive ejaculated alot in the time period. like 3 times in the morning then sex at night is when it would go up.