Ch’i or Qi (氣), meaning energy.

In martial arts, this means that practitioners should use a little energy possible to achieve a great effect possible. In martial arts, Chi is explained as a combination of high-tech skills, physiology, and sports psychology. 

High technical knowledge
The first step is to understand the underlying principles behind the technique, then you can do techniques in the way you use as little energy as possible to get the maximum effect.
As an example; If the opponent grabs your arm and pulls. Instead of rejecting the movement so that it becomes a pull of war, it is better to go with the flow as you perform your counter attack. To succeed you need to have a high level of technical knowledge and be able to do many techniques. You need to train techniques with slow speed which means that you really feel the direction of the force and how you, in the simplest way, can unbalance the opponent. Then you also understand that the block is not a block, but the diversion of energy.

Chi is very connected to the mind.
You can say that Chi-force is the same as Mind power in action or produced optimal situational confidence. In other words, chi-energy in martial arts is equivalent to the world of sports as sports psychology.
The philosophy states that Chi is a vital invisible force that circulates in the body’s invisible meridians. When the energy flows through the body’s meridians, the body is in balance and you feel good.
When the body is subjected to a blow, a blockage of the energy flow occurs, and with, for example, acupuncture, shiatsu, qi gong or t’ai ch’i, the energy flow starts again. 
You go to the doctor to regain a good flow of energy so that your body is balanced and healthy.

Chi is Mind power in action
If we choose to learn ”chi” from a traditional sports perspective, we end up in the field of sports psychology, where you for example with the help of meditation can train your focus to eliminate unnecessary thoughts and visualize achieving goals.
Mind power means learning to use the power of your own mind to create positive and powerful images. For example; you are in a fight and you say to yourself; ”I’m better than you, I shall win!”
Imagine the long-distance runner standing in the world championship arena, with thousands of people watching him; Some of them want him to win, others want him to fail. What will happen if he starts thinking like; I can’t do this, and I’m not good enough, I won’t win … and so on. Without hesitation, he won’t win. Why? Because it was the message he sent to his brain, it was the inner vision he created for himself.
Instead, he should have created a vision where he can see himself running past all the other runners and over the finish line as number one, without even getting tired.

A lot of people spend their lives wishing and hoping for certain things to happen, or for things to change. Others take action and make things happen, make things change. The main difference is that some people have mental blockings, holding them back from doing what they really want to do. But I firmly believe, that the only blockings that exists, are those which you create for yourself!
There really are no limits to what you can accomplish, if you set your mind to it! All you need is determination, attitude and creativity. So clear your mind of negative thoughts, always aim for the top, and never doubt yourself!
The essence of these examples is that the mental image or vision that you create in your mind, will eventually come true.

Breaking
In a way, you can say that breaking is a test to see if you are on the right track in your chi training. You have to focus your strikes trough the target. You need to have the right breathing technique and exhale when you do the strike. You need high speed, strength and maybe you shout; Kiai, to express the power of the strike.

In-depth
If we adopt the philosophy and strongly believe in the force, it gives us the capacity to do things that is beyond the reach of normal humans. This gives us the power to control pain experiences, to overcome physical and mental limitations, to be cured, and to heal others, because we believe in it.
If we choose to learn all our martial arts techniques based on Chi, we become more sensitive to the direction of the force, which helps us make the most suitable defense. You can say that your technique must be done in a way where your chi precedes and controls the actual movement. In this way, you become a more skilled practitioner, and you can say that this is what Chi training is all about. To be your best self.

Important note:
When we believe in ourselves, we increase our chances for success. But it is important to understand that faith cannot be measured, which is the fundamental difference between faith and science. Faith is relying on something that cannot be proven. Meanwhile, the belief, based in the power of thought, the common denominator for all belief systems. But it can become dangerous when a person fails to ex. get well, then other believers can always claim that ”he was not strong enough in his faith.”