Woliveri:
I will share with you the Chi I know, rather than tell you all the Chinese terms and words, I will use modern explaination.
Chi is life force. It is the force created by changing (as in I-Ching). The changing is between yin and young. But you can also say it is between energy and matter. So how good your chi is depends on how good you can handle the cycle of trasfering matter into energy and back into matter and so on. The matter can be say as earth and energy as heaven. In another words, your chi is depends on how good you can represent both heaven and earth at the same time. Most chi masters lost their chi after moved into city. It is because city is build to issolate the mother nature–the heaven and earth. It will be like a fish out of water for a chi master to live in city, it just the matter of time to dry out and die out. It is a good idea to go out to the nature to recharge chi, also to different geographical location to collect different chi since different part of earth attracted different energy form space.
Up to the meridian (ching mai), it is like highway, with lots points (shiueh dao) as market centers along the meridian. If highway in good condition, chi flow strong. But fist must have a good econimy for the chi want to get to the market place first. Then can improve highway condition. For example, the basic ren and du meridian, they have their own purposes, if the mind didn’t support the purposes, the meridian will not improve the travel condition. As ren means to carryout and du means to watchover. Ren wants to completes producing the chemical for breaking down matters, to allow the miximum result, and to collect the final product. Du wants to take in the info. make decision based on the info. and send out orders.
Up to what I know of external, it only focus the mind on the physical/external achievements. That will always cost chi rather cultivate chi. In that kind of focuse, one may cultivate some chi for further external achievements, but the cost of chi will always be greater than the cultivation. That is why not a good idea for thinking of fighting while training, it is a focus/mind issue.
In internal, one only do what is needed to complet the chi cycle–to withdraw matter from the home of marrow, change it into energy, let energy work and result in a most efficient way, collect it, and last, concentrate it, put the wast out and store the useful parts back into the home of marrow. To internal artist, there are no fighting or healing, it is only to complete this cycle as needed. A higher level chi artist can always collect more than what he/she send out. It is like in business, if one didn’t benefit more than what it is cost, it is just matter of time for bankrupt.
So for fighting or healing, it will depend on 1. how sensetive the artist. 2. the artist’s mind/focus. 3. how efficient (smart) the artist used the chi. 4. how good the artist can collect the chi. 5. how stable the artist can remin until the chi was fully concentrated. 6. the environmental chi effects. All that will be factors of losing or not during a chi activaty.
I hope that will help you