Chi Sao is the feeling of energy, more importantly your adversary energy. The literal English translation of Chi Sao from its Chinese origin is “energy hand.” Some also refer to Chi Sao as “giving hand.” All would be correct. First where and then the why of the Energy Hand. The where would be from its origins in Kung Fu or Wushu which are of course the generic terms for Chinese Arts as there are more systems that utilize the drills in one form or another.
The main point of the Chi Sao is to feel your opponents energy so you can anticipate where he is going with his intent and his strikes or grabs if they are a grappler. It is truly a beautiful thing to watch when a traditional practitioner or teacher of Chinese arts demonstrates their version of Chi Sao drills and forms. Most are choreographed although those with skill just do it to whatever the opponent gives them as far as energy in the form of strikes, or more accurately attempted strikes.
Now to the most famous of the energy hand teachers, Bruce Lee. He began his martial arts training from Yip Man his teacher in a style called Wing Chun Kung Fu. This style utilized many of the contact drills, and Lee spent many hours perfecting his skills with a partner.
So the question today, is the technique effective in modern fighting? The answer is a definite maybe. Those teachers who spend vast amounts of time working the Chi Sao drills and teaching them to their students would have to claim that it is very effective in rendering an attackers strikes null and void, and in many instances this could be fact.
Now for the downside. You must be in near constant contact to feel your antagonists energy, which can literally be a pain in butt, or head. What Bruce Lee found out was that in general the Chi Sao must be limited in scope from what was practiced as constant contact in real fights against a trained martial artist who used their hands and not just their feet would be problematic.
What I have found is that Chi Sao is almost useless in sparring. You can still use trapping, lopping (grabbing), and pinning of offending extremities, but the average person is so uncoordinated that energy received is just too slow, and you could more easily just strike them five times than to feel what it was they were trying to do to you.
Lee used the technique more in the first phase of JKD than in its evolution to a more effective combat art, and shortened the drills to more straight line and cross energy defenses and counter strikes. This first phase was for the most part modified Wing Chun. The second phase was more a pure striking combat that no longer practiced the standard Wing Chun Chi Sao drills, but combat modified drills for the fast striking attackers, and the third phase was basically a Ju Jitsu grapplers heaven in which he abandoned all previous methods.
In all the years and research I have never witnessed any Jeet Kune Do (The system founded by Lee) practitioner ever use Chi Sao proper in sparring. The reason I think this might be so, and you are welcome to form your own hypothesis from your own observations, is that the strikes of JKD are so fast and non reliant upon what the target does, that it is almost a not necessary tool. Now am I saying it is not being used? No, just not in the form we are used to watching. As good fighters we are always feeling the other persons energy or intent whether we are touching them or not. Our counters to this energy just dont take on the form of all the Chi Sao drills of the past. Here is a universal truth as far as an attackers energy. If a man touched me (or any good grappler or Chi Sao practitioner) in a completely dark room it would not take much effort to render them to pain city.
Would traditional Chi Sao like Lee taught at his first school be of practical use against a trained combat fighter in arts such as Krav Maga? No not much as the furious strikes involved would not allow for the circular energy motions of old. Possibly that is why Lee modified his Chi Sao over the years until it was abandoned for grappling. So spending too much time on just one aspect of an art as the means to an end of all attacks is foolish.
It is pretty much a universal agreement with combat art teachers that the drills while useful and a good sensitivity drill, do not transfer well into modern combat, so you will see few schools relying on the traditional drills for primary defense.
I have sparred against many traditonal gung fu teachers that try and pull off the moves to their detriment. If your opponent is familure with the drills and what you are doing, it is like being disarmed, and will not offer you the energy you need anymore. I have also seen others do the same scenerio with the exact same results. In sumation, am I downing the drills? No, they have thier place, but know thier linitations, and dont fall victim to thinking that your Chi move is the end all battle tehnique.