Body Mechanics

BODY MECHANICS

Definition: Body Mechanics is the study of proper body movement to prevent and correct posture problems, reduce stress and enhance physical capabilities.

What are Body Mechanics?

How the body moves is a component of Human Factors. Each joint has a certain motion allowed and a typical range of motion. There is also the need for the body to maintain balance that creates instinctual counter balancing movements at times. If you've ever seen a contortionist you have an appreciation as to the types and number of position the human body is capable of. They are not all comfortable or efficient however.

The mechanics of the body are created through the constriction of muscles and the effect that has on the skeleton. To understand body mechanics you must know a little bit about your own physiology and anatomy. But we can use a simplified model for our purpose.
The skeleton is a rigid structure connected through joints that allow for a hinging, sliding or rotational motion of the adjacent bones. Muscles are attached to the bone with a connective tissue (ligaments and tendons). The muscle has two states: relaxed and constricted. When nerve signals hit the muscle it constricts and scrunches itself up so that it is shorter than when it is relaxed. The tendon does not stretch so when the muscle constricts it pulls the tendon which is connected to the bone on the other side of the joint. That causes the bone to move in the manner the joint allows. If you constrict the bicep on your upper arm it moves the forearm by pulling on the tendon that goes across the elbow.
Muscles can only constrict (pull) and relax (stop pulling). They don't push. So muscles are balanced throughout the body so that motion caused by one muscle can be counter acted by another. The bicep on the front of the upper arm bends the forearm at the elbow where as the tricep on the back of the upper arm straightens the forearm out.
Body mechanics gives us insight into how people sit, stand, walk, jump, run, etc. Decades ago high jumpers jumped over the bar by kicking there front leg over it, kind of like the hurdle but 7 feet in the air. Then through a revolution in body mechanics the Fosbury Flop allowed jumpers to manipulate there body and center of gravity over the bar setting new world records that would not have been possible otherwise.
Body mechanics are used in Human Factors work to help represent what the human body and the population is capable of. Anthropometry will tell us if the task can be reached. Body mechanics will tell us what position the body will need to be in to reach it and if it is even capable of doing that. And that will lead into Human Performance.