Other contributing factors that lend to power depend on the angle
of incidence, surface concentration, and penetration. Angle of
incidence refers to your weapon making contact with your target on a
perpendicular angle (right angle to each other) that will render the
greatest effect. Surface concentration is an important aspect to
consider if increased injury is contemplated. It is concerned with the
impact force between weapon and target and the resulting stresses that
occur. It follows the principle of a pin or a nail where the surface
of the natural weapon being used is as small an area as possible in
order to have a more penetrating effect on the target. While surface
injury is at a minimum, the internal effects are much greater.
Penetration refers to the depth of your strike when making contact
with your opponent's vital area (target). Strikes should be designed
to terminate about an inch or two (depending upon the target) beyond
the surface of the target. Since maximum velocity occurs between 70%
and 80% of the way through your movement, it stands to reason that
this is when impact should occur. The reasons for retrieving a strike
rather than following through are two fold: It preserves your balance
and economizes on your movements. After all, a strike that travels
beyond the point intended is really no more than a wasted push.
However, like in most facets of life there are always exceptions. If
the strike is strategically used as a check after penetration (lock-out punch),
it would not be considered wasted.

Ed Parker Sr. Memories
Archived with the permission of Ed Parker Jr.
Ed Parker Sr. was the founder of the art known today as American Kenpo.
In these files, Ed Parker Jr. shares his fathers unpublished notes and other memories with us.