Upright Balance

Maintaining upright balance is fairly easy for humans but it is not innate and is an acquired skill which can be improved. Due to the fact the we are two-legged, humans are naturally unstable. Minor perturbations to our position cause us to have to correct it. This correction is done without any conscious effort and seems simple, but is actually quite complex. Since serious injury can be incurred from a fall, staying upright, or not falling, is very important during combat. Naturally it is also important that little energy be spent to stay upright. To better understand what it takes to maintain upright balance we must first understand static balance, then standing balance and finally walking balance or, locomotive balance.

Static balance

Static balance of an object is achieved when the line from the center of mass of the object pointed towards the center of mass of the earth (or whatever other planet/object is attracting the object) intersects any area between supporting surfaces. This describes when, but not how balance is achieved. To make it easier to understand dynamic balance, an understanding of how static balance is achieved will be helpfull. Since we are talking about static balance, we know that the sum of all forces in our system must be zero (this is a requirement for a static system.) The primary force acting on our body is the force of gravity, applied at the center of mass and pointed towards the center of the earth. This force of gravity must therefore be counteracted by an opposite support force. A support force can only be applied from somewhere within the area between any supporting surfaces. If the force of gravity does not intersect this supporting surface then any force created by this surface cannot be in direct opposition to the force of gravity and therefore cannot sum to zero; motion will inssue.

Standing balance

Standing balance is equivalent to static balance until a disturbance occurs. If a disturbance tilts the body beyond it's static limits it will naturally topple. The human body is not rigid, our joints add another level of complexity to balance. If a person were to not use any muscle force it would be very difficult for them to stay standing. By simply introducing the ankle joint we have effectively reduced the support base to a point, the point directly below the center of the ankle joint. If one were to fall asleep while standing and not be able to use any muscle to maintain an upright posture, balance would be very precarious. But we do have muscles which allow us to make our ankles seem rigid thus increasing our base to at least the width of our feet. Since it would be very tiring to keep our ankles continuously rigid we usually only use our muscle to apply corrective forces in order to restore static balance while leaving our muscles fairly loose otherwise.

Reference: Standing Balance

Internal disturbances

Locomotive balance (walking)

Locomotion

Next subject, Locomotion