Full Push/Pull Muscles Description
[Continued from above] . . . to supply an oppositely directed pulling force that in effect provides the push of the first muscle set.
Basically, the body is made up of a set of levers whose movements copy the geometry of classical mechanics. These levers are powered by muscles, the efficient body components whose day-to-day operation we all take for granted. Many muscles must work together to perform even the simplest jobs. Within each motor unit, muscle fibers obey the all or none principle, meaning that all contract or none contracts. If the muscle fibers of a motor unit are stimulated enough by nerve impulses to contract at all, they contract to the maximum. Yet such force is only possible through the arrangement of the muscles, bones, and joints that make up the body's lever systems.
Bones act as the levers, while joints perform as living fulcrums. Muscle, attached to bones by tendons and other connective tissue, exerts force by converting chemical energy into tension and contraction. When a muscle contracts, it shortens, in many cases pulling a bone like a lever across its hinge. Muscles move and by their motions we move. We are capable of performing a wide variety of actions, but despite this, muscle itself moves only by becoming shorter. They shorten and then they rest - in other words, a muscle can pull but it cannot push. But together with their antagonist muscle pairings, the push/pull muscles provide us with a complete set of motions.