Qigong and high kicking

DOes JKD have an internal side, Bruce Lee very refers to the 'flowing energy' and making your arms heavy. I attended a qigong class and was pretty amazed by the results one can achieve with COMPLETE relaxation and full hip mobility..... Both of which that Bruce Lee emphasised but i have no recollection of him talking bout the breathing exercisese that go to maximise the effect of these. He Talks about chi w.r.t. his one inchpunch and exploding the power out of your fist but never any cultivation of chi exercises... I assume studying WC for so many years he must have come into contact with its internal side which would encompass these things... being good at chisao can be likened to your formation of good rooting through chi exercises.

Also though in Bruce's books (and films) he uses and describes head kicks all the time but any other JKD books but people like Hartsell, Tackett, and Davis II dont really contain any high kicks and in my JKD school i havent seen many at all either, why is that??