When water is rushing through a fire hose at a high pressure rate, and flowing out of the nozzle, it is nearly impossible to bend sideways. This is due to the internal strength of the water flowing within.

This is the same energy that is used in internal martial arts, and is strenghtened with the training method 'Unbendable Arm', made famouse by Aikido Grandmaster Uyshiba.
See : http://aikidoforbeginners.blogspot.c...dable-arm.html