My friend Ok Chang-yang, a student of The Way Martial Arts Academy of Seoul modelled the postures for the article.
Coincidentally, a little after submitting my contribution I stumbled onto another martial art blog focussing on Tai Chi, who also wrote something on posture: "Body Should Maintain an Erect Posture." The author quotes Yang Cheng-fu:
“The body should maintain an erect posture without leaning; spine and tailbone should hang in vertical alignment without inclining. Beginners must pay special attention to this as they execute active movements involving opening and closing, relaxing the chest and raising the back, sinking the shoulders and turning the waist. Otherwise it will be difficult to correct this after a while and will lead to stiffness. Even though one may have devoted a great deal of time, there will be little benefit or practical advantage” (Yang Family Secret Transmissions, p. 5-6).
There are a handful of martial arts that really focus on keeping an erect posture. These include such styles as Tai Chi, Aikido, Karate and, of course, Taekwon-Do. Interestingly, while Taekwon-Do has developed out of Karate, for me the erect posture in Taekwon-Do is more similar to Aikido and Tai Chi, which are soft styles, than hard style Karate. In Karate their seems to be a kind of rigid stiffness to their erect posture. I'm not sure what the reason for this, but I'm sure they must have one. Also, the focus is on deeper stances in Karate. Tai Chi also has deep stances, yet with a great emphasis put on a relaxed musculature. In Aikido and Taekwon-Do a higher stance is preferred and while emphasis is put on an erect posture, equal emphasis is placed on relaxedness. While Aikido and Taekwon-Do prefer higher stances (that is not to say that they do not employ low stances, I'm merely referring to the stance preferences in these styles), these styles also emphasize a low centre of gravity seated in the danjeon 단전. (I wrote about the danjeon somewhere else.) Generally Taekwon-dojang outside of Korea do not use the term danjeon, but merely refer to the waist or hips. When referring to the hips or waist, we are often actually referring to the danjeon. In Aikido and Taekwon-Do we often use taller stances, but always ensure that our centre of gravity is low, at the danjeon.
Working on a healthy erect, yet relaxed, posture is a very important part of ITF Taekwon-Do training.
Below are some links to posts on posture from other martial art blogs and websites: