Even the conflicting comments on you tube seem to have no idea??? The title "Spannungssimulator" translates to "VOLTAGE SIMULATOR" ??? HUH??
Looks like they are showing how trees/limbs can be under dangerous tension when you're cutting - on some fancy contraption.
Not all if you look at the entire situation. He was standing on the safe side of the log so that if the log were to release suddenly, It would do so away from him.
It is a dead fall simulator showing tension possibilities in order to train woodsmen and forestry classes for the clearing of fallen timber that is under tension. Of course in a controlled setting so no one gets hurt. No experience like real experience tho.