Oi-zuki, lunge punch, pursuit punch - a punch linked with a forward lunge step.Its one of the first things that a new Karate-ka learns. Its been over 15 years since I first learned how to punch(and even longer if you consider I was a teenager when I started TaiKwonDo). But recently I found that I can still learn about it.
This is one of the things I love about Karate. There are no answers, only further questions. Further leaning. Going deeper. Fortunately there was a Tsuroka-Sensei clinic in Ottawa recently and although I was unable to attend the information still made its way to me.
This time it is about the strength of the punch and achieving full strength by using relaxation of the lats and pecs on the punching side when transitioning to full extension and then at full extension tightening them. The hikite side keeps the lats and pecs in tension.
Kiai is also important in this process but timing is paramount. The kiai tightens the muscles so only kiai at full extension.