I have had the very humbling privilege of training with some extremely high ranking Hapkido Grandmasters including the honorable Grandmaster Ji Han Jae, Grandmaster In Sun Seo,  who both demonstrate "Ki energy regularly". All Masters and Grandmaster have a somewhat different idea of "Ki". Each has given me an entirely different description of what "Ki" energy is. Grandmaster Ji Han Jae explained Adrenaline has alot to do with Ki energy, I believe this to be true. From all of my research, here is how I describe "Ki Energy"; 

 "It is when all energy sources come together. We have physical energy from our body, mental energy from our mind and spiritual energy. The body can only produce maximum energy when all of our internal organs are in balance, proper diet, nutrition, proper hydration. The energy sources which power the nervous and muscular systems of the body can only flow uninterrupted when we take proper care of our bodies. 

Our mind can only focus maximum energy when it is clear and unclouded with negative or unnecessary thoughts. Our spirit can only provide maximum energy when we are unwavering in our will to succeed and survive and when this spirit is indomitable regardless of the odds. This together with proper rooting of stance and proper connection to our opponents weight and center approaches my concept of "Ki". 

When it is all at the optimum, all connected and focused on the task at hand and the adrenaline can flow freely, uninterrupted and unclouded by our mind and spirit we are probably experiencing what the eastern cultures have referred to as "Ki or CHi energy" (in my humble opinion). Each one of these categories, Physical Energy, Mental Energy, and Spiritual Energy can be broken down into categories and discussed at length, however for the sake of a relatively brief description, that is my position on "Ki Energy".

- Master Frank S. Ehnle 
Royal Dragon Martial Arts
American Hapkido Federation