The relaxation-tension-relaxation sequence of body control allows the body to apply power quickly and smoothly to a technique. Relaxation helps disconnect the arm or leg from the body so it may move with greater quickness. In the execution of a technique, the entire body must relax initially so it may move quickly and powerfully. Then snap the arm or leg at the target. At the instant of impact, the entire body must tense (especially the abdomen) so it may transfer energy to the opponent and absorb the reactive jolt of the impact that will ripple back through the body. An instant later, the entire body must relax so it may quickly recover to a defensive position.
There are two kinds of muscles in every movement. Agonists are the muscles which contract and make the motion happen. Both sets of muscles cannot tense at the same time. If the antagonists are tensed during a motion, they will slow the motion and possibly be injured.
Power is a combination of strength and speed. Strength comes from tension and speed comes from relaxation. The body should be relaxed until the moment of impact. Even then, the tension only lasts for a split second. A most common mistake is to tense the wrong muscles at the wrong time.
There are several wrong times to tense the body:
- At the beginning of a movement. Typical symptoms of this mistake are grunts, gritted teeth, tensed neck, shoulders pulled up near the ears, and chin pulled down. The first motion of any movement must be sudden and explosive, no preliminaries or useless motions.
- At the half-way point of a motion. For example, in the front snap kick. The foot comes off the floor and the knee comes up. Beginners tend to stop here for a moment and then continue the kick. To do this, they tense the leg and body and the head bobs. People also tend to tense at the start of the last part of stepping, attacking, and blocking.
- Tensing body while kicking. During kicks, the upper body should be completely relaxed, with the hands ready to attack or defend.
- Tensing too long at the point of contact. The tension at the end of technique should last only a slit second. The duration of the tension depends upon what is intended. If muscle conditioning is being emphasized, then a longer, isometric contraction may be used. In a split second snap back technique, power is derived from the motion of the body, rather than locking into the technique.
- Tensing unnecessarily while waiting in a stance. Some muscles are needed to maintain proper posture, but many people tense too many muscles, and much harder than needed. As a result, they are rigid and immovable. They must relax to move, but by then it is usually too late.