That you can increase martial arts chi power by relaxing is at once zen, and frustrating. Oddly, it doesn’t have to be frustrating, it merely needs to be understood. Key to understanding this is understanding what ‘type’ of relaxation is required by each art for that art to cause manifestation of chi power.
Before we go into this by individual art, one thing needs to be understood. Relaxation is the key to power. It would not be overly incorrect to say that the body is a machine, and the mind is a radio transmitter. This means that the machine, and the transmitter, need to be cleared of all static if they are to operate at maximum efficiency.
I prefer teaching the art of Karate first, as this is a simple art that can generate massive amounts of chi. It deals with pure explosion from the tan tien, though, the sad truth, most people treat it like a calisthenic. One needs to stop doing exercises without thought and invest their awareness if they are going to create the intrinsic power of the martial arts.
Breath gently and learn to relax the body, and tighten only the fist. The body might be taut in the beginning, as one learns how to align it correctly and connect it to the ground, but this tautness should give way to a relaxation that can withstand the introduction of force to the frame. The fist does not have to be excessively tight, just tight enough to emphasize the space surrounding the moment of focus.
The real secret to higher martial arts is to move energy through the body while the body is in motion. This can be done in Shaolin martial arts easily; the more the circular movement, and the more awareness given to proper alignment, the easier it is to do. Again, breath and relax even while handling the application of weight to your frame.
The highest martial arts are such as Pa Kua Chang and Tai Chi Chuan. The reason for this is that the slower you go the more you look, the more you look the more you know. This is the concept of investing awareness brought to its peak.
Myself, I have done walking the circle and the Tai Chi form to the point of one move a minute. If I stop totally, this is called pile stancing, and it is very effective. I usually do stoppage merely to take the time to assess the form and make sure everything is in the right place.
In conclusion, no art is better than any other art, they are just different pieces of the same puzzle; there are no superior combat disciplines, merely superior martial arts students. Learn to relax, even while exhausted, and you will find that there is no fatigue, only a pathway to more energy.