To make matters more complicated, during the initial stage (which we may be talking about months to years of practice depending on the diligence of a student and whether he has good guidance), the cultivation of chi can best be done through normal/natural breathing. But then when we practice with normal/natural breathing, how can breathing be related to chi kung? The reason is that with natural breathing our mind can be better focused on the qi-generation process (which essentially is transformation of our breathing energy into chi-energy, the postulation of myths, visualization, imagery, doing mantra, counting breaths etc are tools to aid this focusing process, instead of the source of chi, which is energy transformed from our breathing mechanism).
And yet to make matters even more complicated, after the initial stage (in professional lingo, after one has entered the door），a practitioner has to learn the method of reverse abdominal breathing to generate a substantial amount of chi essential for further progress. And only a substantial amount of chi would be qualified to be the classical Taoist 炁. How about learning reverse abdominal breathing on day one? The problem is, before proper groundwork in meditation under normal breathing, RAB will be of no use to our practice. Worse, some practitioners will get tightened up through forcing themselves doing the not-so-natural RAB.
As you can see, we are again back to square one: Do normal/natural breathing in the initial stage. A good advice from many good teachers!
The positive side is, if you can do it diligently, one day, your teacher/coach/sifu will ask you to start doing RAB. Or if you practice solo (or solo after a period of guided study), and assuming that you do it almost daily and diligently, one day, your body will tell you or push you to do RAB - good luck, you have entered the door...