Tense as in contracting the arm muscles to stabilize it (isometric contraction)? Some engagement is necessary to stabilize the limb so that the power from the legs, waist and torso is channeled to the fist, but all striking arts that I know of aim to limit that contraction to the very minimum, as it acts like a "brake" that makes strikes slower and weaker.if I tense a bent arm, am I not engaging the biceps then?