As you may, or may not know, Ki or Chi is what the characters from Dragonball Z use to perform such attacks as the Kamehameha or the Masenko. But did you also know that Ki and the philosophy of it has it's roots in Ancient Korea, China and Japan.
The Ki principle is that Ki is a universal energy that humans can harness and use to their own benefits. Akira Toriyama took this idea to the extreme and made it so that people could use Ki to shoot fireballs of energy after they had trained their Ki enough.
The first written account of Ki came in the third century BC. It was described in the Huang Ti Nei Chung Su Wen (The Yellow Emperor's Classic of Internal Medicine). From China, where the text originated, it was passed down into Korea in approximately 200 BC. Soon the principles of Ki were used by Hwa Rang (Flowering Youth), the warriors of the Korean peninsula. They used the principles of Ki to enhance their physical and metal power, just as the Z warriors do.
The Yin/Yang theory is key to the Ki theory. It describes how everything in the universe is in balance. For example there can be no day without night. There can be no hot without cold. There can be no life without death, and so on. In the Yin/Yang philosophy, Yin is negative and Yang is positive. Yin is the earth; Yang is the heavens. Yin is cold; Yang is hot. Yin is female; Yang is male. Yin is emptiness; Yang is fullness. Yin is white; Yang is black.
On the left is the Yin/Yang symbol that I'm sure most people are familiar with. This shows that within all Yin there are traces of Yang, and within all Yang the are essences of Yin. For the Ki practitioner heath is a balance between the two forces, and illness is an imbalance. Also Yin and Yang must both be experienced by the Ki practitoner and must be in harmony with both. In this way Ki energy can be utilized in a fashion that is acseptable in nature.
The knowlage of Ki was passed on by the monks and priests of ancient Asia. From China, the knowlage traveled to Korea and then, much later, to Japan. In ancient Korea the Hwa Rang were taught the prinicples of Ki by Buddist monks. these monks through years of meditation had taken their knowlage of Ki to such a point that it was no longer a means of balancing the Yin and Yang in their body. They taught this advanced Ki training to the Hwa Rang, who used it to strengthen themselves for battle, just as in Dragonball Z.
It was in the fouth century AD that the knowlage of Ki was first brought to Japan. But there is no evidence of it being put into practice until Buddhism as introduced in AD 602. But during this time Ki knowlage was mainly used for medical purposes. It wasn't until the 12th century that the priciplas of Ki were first applied to battle, with the advent of the Samurai. This merger of Buddhist philosophy and military prinicples gave birth to martial arts such as Aikido and Korean Hapkido. All madern martial arts use the priciples of Ki as their primary basis of physical and mental self-defence awareness.
It is due to the pricipals being the basis of all martial art, that Akira Toriyama was able to adapt the phiolophy of Ki and take to the extreme. I hope this insight into what exactly Ki is has been of interest to the Dragonball Z fan. Thanks to The Ki Process by Scott Shaw.