Muscular Balance

One of my many interests in anatomy education is muscular balance; this is not a term I have invented - it is also known as, or referred to as kinetic balance. I usually explain my concept of muscular balance in the following way:

Consider a wooden post - perhaps a tent-post, or a flagpole. The stability of these columns depends on the positioning and strength of, supporting ropes.

Each of our skeletal joints has a similar reliance on supporting structures - the tent-post has ropes, our skeletal joint has muscle tissue.

The vertebral column is a great example - a long, slender column, supporting the cranium at the top, assisted by supporting cables; but as we understand, this vertebral column is made up of more than 30 individual joints. Nevertheless, we could view each joint separately, each pair requiring cables to control steadiness, or movement, whatever is required.

Let's consider a small section of the vertebral column, the cervical region; for many of us, our daily occupation requires us to be positioned over a :

treatment table,

a food preparation bench,

a computer desk,or

a computer.

There are many other occupations, I understand, but, unless you are, for instance, leaning back, painting the ceiling of your home, your vertebral column, including the cervical section, is usually in flexion, chin towards your chest. This suggests that the flexor muscles, at the front of your throat, are in some degree of tension, pulling your head forward. This is an incorrect assumption.

The head can sit in this forward position, under its own weight, without any assistance from the anterior muscles; only the extensor muscles at the rear, are active, as they pull back on the cranium, controlling its flexed position. This means that for much of the time spent at a desk, reading, or whatever, the flexor muscles are almost completely idle, while the extensor muscles are active.

One of the results of this overactivity of one set, and underactivity of an opposing set, is muscular imbalance; the extensor muscles maintain their strength, and their tone, while the flexors become flaccid by comparison. Our imaginary flagpole is now supported by a set of ropes on one side that have strength and tension, and an opposing set of ropes that are relatively weak, and slack. This means the complete assembly is adversely affected.

If we imagine the experience of a rear-end collision involving a couple of motor vehicles, the driver of the forward car, hit from behind, is forced into cervical extension; his head thrusts towards the head-rest, if there is one. There is insufficient time for the flexor muscles to contract in an attempt to limit this rearward movement - perhaps their flaccidity adds to this delay.

The head bounces off the support, possibly at the same time that the flexors respond, and there could be a series of this shuttling back and forth, all in a few seconds, until coming to rest.

This is a theoretical script of the scenes in such an accident - investigators more knowledgeable than I would be able to describe the details more accurately; I want you to consider the structure, and contemplate, in your own mind, the effect of muscular imbalance on the cervical spine, in even less dramatic circumstances.