62 Yoga anatomYBones support weight; muscles move
bones. There is an enormous difference between
how the muscles work when they are moving the
bones into place to take weight and how they work
when they are actually attempting to hold the
weight themselves.
When the muscles take on a weight-bearing
function, they overwork and become rigid and
fixed. If the bones bear weight instead, the muscles
can stay constantly moving and continuously make
micro-adjustments to create efficient movement
and dynamic stillness rather than disconnection and
locking in the joints.
Muscles work best when they can calibrate tone. The basic definition of the word
tone is readiness to respond. A tissue that has high tone needs less stimulation before a
response is elicited because the tissue is more prepared to respond. On the other hand, a
tissue with a lower tone needs more stimulation before a response happens.
Although it is related, this is not the same thing as sensitivity. A tissue can be very sensi-
tive and have low tone. It might register a stimulus at a very fine level but not react until
it receives a great deal of that stimulus. Alternatively, a tissue can have high tone and low
sensitivity, where it is very ready to respond but not actually responding because it isn’t
picking up any stimulus.
All tissues need to be able to change tone in response to changes in the environment,
both internal and external. The important thing is not the absolute state of tone but the
tissue’s ability to adapt.
If the tone of a muscle or group of muscles is too low, when a muscle is needed to par-
ticipate in a task it might not be readily available and other muscles must compensate. This
can lead to imbalances in the joint space, ligament sprains, and muscle strains.
On the other hand, if a muscle or group of muscles is too high in tone, the muscle tissue
burns more energy than is necessary, is more likely to overwork, and creates imbalances in
the joint space that lead to injury.
Because the muscles have a rich supply of nerve endings, they are able to calibrate their
tone to a very sophisticated degree. This means that they can be incredibly efficient about
using just enough effort to get the job done.
Muscles calibrate tone and cultivate awareness through negotiating resis-
tance. The nervous system receptors in the muscle tissue are called spindles, a specialized
kind of proprioceptor, or self-sensor. One of the things that they sense is what happens
in the muscles when they meet resistance. These proprioceptive spindles then use that
information to set the level of tone for the muscles so that each muscle can meet or match
the resistance it encounters.
Muscles build tone by meeting greater and greater amounts of resistance. Resistance is
an essential source of feedback for the proprioceptors and is based on sensing the relation-
ship between the muscle tissue and the source of resistance (often gravity). When a muscle
has the opportunity to engage with many different degrees of resistance, it learns to adapt
and calibrate its level of tone.
When there is no resistance, the nerve endings in the muscles get no feedback, and the
muscles don’t have the ability to use the nerves to sense changes in tone or to make finely
tuned adjustments to the muscle tone.^5(^5) The nervous system is not the only way that we get information about the body. Cells are able to communicate with each
other directly and through the fluid systems of the body; juxtacrine, paracrine, and endocrine signaling are examples of this.
An enormous difference also
exists between the weight trav-
eling clearly through the bones
and the weight passively hanging
in the joints. In this case, when
we hang in a joint, the ligaments
around that joint must negoti-
ate the weight, and the weight
doesn’t translate clearly from
bone to bone.