Video at the bottom of this page where we look at shomen hanmi and the use of the legs, whilst punching kizami-zuki and gyaku-zuki.
Kizami-zuki and gyaku-zuki from front stance.
My karate instructor always referred to hanmi and shomen as, Hanmi = side facing and Shomen = Square facing.
Shotokan karate dojo should place tremendous importance on this area of practice.
When executing Kizami-zuki (lead arm punch), the body and hip are in the Hanmi (side facing) position, then when gyaku-zuki is executed, the body is in the Shomen (square facing) position.
When first starting shotokan karate, the karateka will be told that hanmi is used for the basic blocks in front stance and shomen is used for the two basic punches oi zuki (stepping punch) and gyaku zuki (reverse punch).
Try not to over extend on the punches, it is also common to over twist the body in both directions. Start both punches by driving from the back leg.
There are different ways to use the legs with these punches, in the video we tighten the inside of the the thigh muscles on impact of the punches, this causes the front leg to pull imwards very slightly, in my opinion this way is much stronger and more stable than keeping the knee still, or as some karateka do, push the knee outwards.
This shotokan karate exercise is a great way to practice shomen hanmi, so many karateka have little or no hip and body movement, so focusing on this area is imperative to understand the fundamentals of Shotokan Karate.
Kizami Zuki and Gyaku zuki
Kizami Zuki and Gyaku zuki in Zenkutsu Dachi