Cross training is a term that has been long used in the athletic community Coaches, whether amateur or professional, have long acknowledged the benefits of exposing their athletes to training methods, concepts and strategies of sports other than those they are training their teams or athletes in. From my early school days through my college sports, cross training was not only accepted, but encouraged. However, this was not the case in the very traditional and close-minded martial arts community of the 1950s and '60s. There were few martial artists who dared to look into arts other than the one they represented. Among those who did see the value of cross training was Mr. Ed Parker, my Kenpo karate instructor. My Sifu, Bruce Lee, was another.
Decades ahead of his time in his fervent pursuit of martial arts knowledge, Sifu Bruce Lee literally left "no art unexamined and researched." Sifu Bruce had the most extensive martial arts library of anyone I have ever met. Not only did his collection consist of martial arts books, but also of body building, nutritional and philosophical publications.
During my training with Sifu Bruce Lee, he was always introducing me to various books that would help my growth in the martial arts and in my personal life. One of these books was The Art of War by Sun Tzu, which contains many principles and concepts that are still valid today.
In this book, Sun Tzu states, "Some people are intelligent in knowing themselves, but stupid in knowing their opponents and with others it's the other way around; neither kind can solve the problem of learning and applying the laws of war".
If you only know yourself and the system you practice, you are only 50% prepared. Sifu Lee knew that, to understand and deal with combat, you must know what other styles and individuals practice and specialize.
During my course in training with Sifu Bruce, he was always researching and experimenting with different tactics and modes of attacks. Sometimes Sifu Bruce would have me attack him in a method from a system or style he was unfamiliar with, to see what response he would instinctively react with.
When I first started training with Sifu Bruce, he was in the midst of creating a "system" of combat that centered around a modified form of Wing Chun -- a blending of his modifications and ideas on the strategies of Western boxing, and then using the principles and tactics for Western fencing. He took kicking from different systems, including Chinese and non-Chinese systems, then customized it for himself.
He was into investigating every known system that he was exposed to during that time period. During this time, he even taught me different sets and forms from a few Chinese systems. He then moved away from this type of training.
I have read in some martial arts publications that he didn't practice the Filipino martial arts such as Eskrima and Kali, and he therefore didn't integrate these arts into his personal system of Jeet Kune Do. While this is true, he was exposed to Filipino martial arts many times by me and, although he may not have put it into his personal system of combat, he did on many occasions practice with me the single stick, double stick and olisi toyuk (nunchaka).
Many people say I taught him the olisi toyuk (nunchaka), single stick and double stick. I like to say I shared with him and demonstrated and practiced with him. We also experimented with light sparring with single stick, double stick and olisi toyuk. So, in my opinion, he practiced the Eskrima and Kali on a small scale to research it, and to put elements of the nunchakas, double stick and single stick in his movies.
You will also read in martial arts publications that Sifu Lee only used Chinese martial arts. Again, this is incorrect. Techniques he modified, equipment he used and principles and concepts he utilized were from many different disciplines and systems.