muscular sYstem 63
Muscles pull. In a concentric contraction, the pulling power of the muscle is greater
than the resistance. In an eccentric contraction, the pulling power of the muscle is less than
the resistance. In an isometric contraction, the pulling power of the muscle is exactly the
same as the resistance.
In all of these cases the muscle is firing and the molecules in the myofibrils are ratchet-
ing together to pull. The muscle is never actively pushing the fibers in a way that slides
them apart—that happens because the resistance is greater than the pulling force being
generated.
So, how is it that we can push something away? Any joint movement includes a part that
is lengthening and a part that is shortening. Whether or not the joint is flexing, extending,
or rotating, some muscles are lengthening and some are shortening. The shortening muscles
are concentrically contracting; the lengthening muscles are in various degrees of relaxation
or are eccentrically contracting.
Flexibility and strength are about the relationship between the nervous
system and the muscles. A classic definition of flexibility is the ability of the muscle
to lengthen, and a classic definition of strength is the ability of the muscle to generate
force and speed. Both flexibility and strength in the muscles are functions of the nervous
system as much as they are functions of the ability of the muscle fibers and connective
tissues to adapt in length.
In the vast majority of situations, flexibility is not determined by the actual physical length
of the muscle or of the muscle fibers that compose that muscle. The resting length of the
muscle, its tone, and the amount it will lengthen are all set by the proprioceptive nerve
endings in the muscle. This setting is established in the nervous system through previous
experiences regarding what is appropriate, safe, and functional.
The amount of strength a muscle has is more dependent on its physical properties,
including the actual number of muscle fibers. Muscle strength is also a product of the way
that the nervous system recruits fibers and organizes the surrounding muscles and kinetic
chains. When the nervous system is inefficient in the way it recruits and organizes muscles,
it diminishes the functional strength of a muscle by creating a situation where the muscle
has to exert effort to overcome resistance from other muscles in the body.
Increasing flexibility and strength is a process of reeducating the nervous system through
conscious attention and practice as much as it is about stretching and repetitions.
conclusion
Muscles surround joints and wrap around bones in incredibly sophisticated spiraling layers.
Embryologically, muscles follow fluid pathways from the center of the body out into the
limbs. The three-dimensionality of the pathways of the muscles allows them to have incred-
ibly nuanced effects on the bones that they move.
In a three-dimensional paradigm, it is clear that for each individual, the muscles weave
together into unique patterns of dynamic lengthening and shortening that create the move-
ments of daily life, such as walking and talking, opening a bottle, or brushing teeth. What
creates integrated movement for one person is not the same pattern that creates integrated
movement for another.
When traditional ideas about muscles shape our movement choices, we end up with
faulty generalizations and assumptions about the role of muscles in creating movement
and support.
What happens when we expect that in any given situation every person will use his
or her muscles in the same way? That there is a “correct” sequence of muscle actions to
perform a movement? That this way works for every person? And, that working harder
makes a person stronger?