In star Wars the hero, Luke Skywalker, is mentored by Obi Wan Kenobi, who
spoke of the Force as an invisible energy field that "flows through us".  Many of
us that practice the martial art of Aikido believe that ki energy is similar in that it
also in the central focus of our power.  There are two important concepts, which
help us develop ki:
-The Unbendable Arm
-Breathing to Relax the Mind

The Unbendable Arm – Among the first questions asked by new Aikido students
is what is this force and how do we know when we have it?  Many have heard
the story of an individual generating the strength to free a loved-one
trapped underneath a heavy object.  We imagine the power of ki as an untapped reservoir akin to the mass of an iceberg, which lies under the surface of the ocean.  One of the first ki training exercises is Orenaite also known as the unbendable arm.  Ki flows through the healthy body continuously and can be redirected to focus power in a specific location and direction.  To help our students visualize this concept, we ask them to extend one arm straight and to imagine directing an imaginary stream of water from our center, through our head and out the arm in a powerful stream focused on putting our water.  What we find is that this relaxed arm can be held straight much more powerfully than trying to consciously hold it straight with muscle power.  This imaginary water is our visualization of the flowing ki energy.      

Breathing to Relax Your Mind – The key to ki (no pun intended) development is
to learn that real power and movement comes from a relaxed mind, which
creates a relaxed body. If the mind and body are unified, ki flows in an
unrestricted manner. The catch is in unifying the mind and body. The more
extraneous thoughts we have, the more clouded our mind becomes, and the less likely it will be for our mind to achieve a relaxed state. In order to retrain
ourselves to unify mind and body, we must train our body to "obey" our mind.
This is achieved first by training your mind to be calm and relaxed. Aikido
practitioners often use a technique called Misogi breathing to focus our efforts on this type of training. In this exercise, the students sit upright with good posture (in seiza or zazen) while imagining that we draw breath into our nose, through our mind and fill our center (one-point) as if it were an infinitely large reservoir. Our exhalation retraces the path from our center through our mind and out of our mouth in an "ahhhh" sound. During inhalation we imagine our one-point as expanding to an infinitely large size, and contracting to an infinitesimally small size during exhalation. It is through this process that we can train our mind to focus on this activity and begin to relax as extraneous thoughts fade away. An ultimate test of this mind-body control is to perform misogi breathing immediately after a strenuous workout. It takes a substantial amount of mental focus to relax and achieve full inhalation and exhalation without gasping. It is through this process that your mind can achieve control of your body and relax even in the face of the randori (multiple attackers). The relaxed mind sees clearly in the same way that a lake clearly reflects a mountain in the distance clearly.

Ki energy is like the Force in that it is invisible and the source of a tremendous
amount of power when executing Aikido techniques. This energy is maximized
when the mind is relaxed. Techniques such as misogi breathing help the student to develop ki energy to tap the enormous power which lies just under the surface.