I train in Taekwon-do (1st Dan Instructor) and ninjutsu (Beginner) and I had an interesting insight/question arise from my ninjutsu Instructor (which is why I picked up the second art):
In ninjutsu's Shizen (almost like TKD's Outer Open Stance, so a 50/50 weight distribution per LEG), we are supposed to bear ~2/3rds+ of our weight on the ball of the foot, and only ~1/3rd on the heel. This is to produce a more assertive stance that is more agile as well as better able to better absorb a hit from the front.
For me, this made a lot of sense as in Ice Hockey if you are caught on your heels you end up on your butt. Plus the shape of the human foot; a long-ish forward platform (the tarsals + metatarsals) with a rounded back that does not extend to the rear (the heel). If you are caught with too much weight behind, that rounded heel will dump you over.
I brought this question to my Taekwon-do instructors (2nd, 4th and 6th Dans) and it was pretty clear that they had never thought about it in this way either. The question is still open on the TKD side (we are all having a think about it) but they seem to think it's a 50/50 weight distribution across each FOOT (50% heel, 50% ball of foot).
So... why would you place more weight on the forefoot (ball of foot)? Why would you have an equal distribution between the ball of foot and heel? Why would you place more weight on the heel? I'm interested in some overall views on this that are generally applicable to stances, as well as views from how other martial arts use this "adjustable feature" of a stance.
IE: TKD's L-Stance (aka Back Stance) has a weight distribution of 30% on the front LEG, and 70% on the back LEG, but where do you carry that 70% on the back FOOT?
I once again spoke with my ninjutsu instructor about this, and he mentioned that Yoga practitioners have a concept of 4 points of balance and weight distribution per foot; outside-ball-of-foot, inside-ball-of-foot, outside-heel and inside-heel. Again, from an Ice Hockey players perspective, this makes a lot of sense (and makes me wonder why I've never thought of it in this way before). Ice skates have 2 edges; an inner and outer edge. It is also important to keep your weight centered over the blade for a neutral stance, and forward for an aggressive/fast stance. As Ice Hockey skates are rounded (you never have more then 1-2cm on the ice at a time), it's of course important not to rotate too much weight back (else you're on your butt). So, in Ice hockey, you have inner and outer edges, along with forward and back/neutral, so like Yoga, there are 4 points of balance on each foot.
Anyway... Yoga having 4 points of balance per foot is fascinating to me in relation to this question. So... does anyone else have a deeper understanding of how this concept applies to distributing your weight in relation to martial arts stances? What advantages would you gain by having a majority of your weight on the outer-ball of your foot? When you spar, where do you carry your weight in relation to these 4 zones of the foot? Why?
More MORE INFO...
I found a decent video on Yoga's concept of the "4 corners of the foot": http://www.youtube.com/watch?v=6bk6zBPs79g . It focuses on muscle engagement / development as well as awareness of these 4 "zones".