Here's a video from two-time U.S. Olympian Nick Del Popolo on how to get inside the defensive stiff-arm using the "chicken-flap" method. The other side [...]
A key concept in martial arts is to stay relaxed. Tension equals reduced power. Stay relaxed and all possibilities are open to you. According to this Ted talk, standing in a power pose can temporarily increase your testosterone and reduce your cortisol. Cortisol is one the so-called "stress hormones" and can lead to reduced performance in all areas.