Two Models of Motion

Monday, November 29, 2004

Two Models of Motion

I have found it useful to divide motion into two types, ballistic and external load supporting. The characteristic of the former is typically that you are throwing something, normally something reasonbly light, and looking for high velocity. The characteristic of the latter is that you are trying to exert force, a push or a pull, on a resistant object. There are somewhat different bio-mechanices required to deal with the differing situations.Ballistic Motion
In order to pick up velocity, you need to have a relaxed body. The recruitment of the body must allow for an increase in speed at each stage of the motion. One of the key factors in this is the ability to tune the body’s elasticity, so that the body can flex and extend with the right stiffness at each joint. The goal is to maximize speed in a particular direction, and also maximize kinetic energy. Kinetic energy is proportional to the square of the velocity, so anything you can do to up that quantity pays nice dividends.

Load Bearing Motion
If you are in contact with a large and resistant mass, you need to exert force. This is true regardless of whether you arrived there at high velocity or not. The force requires good body dynamics, but also the requirement for elasticity changes. In this situation, you need to take advantage of the cumulative power of the body, and accentuate it with the ground reaction force and with the force of gravity.