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The Myotatic Reflex

The Myotatic Reflex (sometimes myotactic reflex) is probably our body's most unrecognised and unappreciated defence mechanism.

Forget about the immune system. When it comes to making it safely through the day, nothing comes close to the myotatic reflex.

Imagine that a muscle is able to constantly monitor it's own length and tension no matter what it's length, and is able to respond the instant it's length or tension changes. Without the myotatic reflex, controlled movement would be impossible.

The myotatic reflex starts in the muscle spindle which constantly and spontaneously produces an afferent impulse to the spine and therefore the brain - at a rate of at least 5 - 50 times per second.

Any little change in tension or stretch in the muscle will increase this feedback to spine and produce an rapid increase in muscle tone.

The Myotatic Reflex

We know this as the knee-jerk reflex. A sudden increase in quadriceps length induces a quick firing at the anterior motor neuron.

Watch this animation to see it in action

The significance of the myotatic reflex is how it prevents damage to joints. When it is working properly, joints are protected from excessive movement or strain.

If the reflex is inhibited, joint will be damaged - causing pain initially, and osteoarthritis in the long term.

Assessing the patency of the myotatic reflex is the key to proprioceptive muscle testing and faster patient recovery.

Dedicated to strengthening your practice,

Simon King B.App.Sc(Chiro) DIBAK
www.expertmuscletesting.com

The withdrawal reflex

In the last blog I showed how the myotatic reflex works to prevent our body being damaged by an outside force.

The withdrawal reflex (also known as the flexor withdrawal reflex) also exists to keep us safe.

Whenever our skin is stimulated, our muscles respond appropriately to remove us from harm's way.

This reflex can be stimulated by a wide variety of factors.

• Heat (touching a hotplate)
• Sharp (standing on a tack or a thorn)
• Deep pressure (a pebble in your shoe)
• Light pressure (tickling your foot)

When this reflex is activated, certain muscles contract to pull us away from the source of the irritation.  Naturally, (according to the Law of Reciprocal Inhibition) when any muscle contracts, it's antagonist must be at least partially inhibited.

In other words, our skin is almost hard-wired into our muscle system (via sensory reflexes and the nervous system).

Most of the time, this sensory stimulus is transient and our muscles return to normal as soon as the threat is lifted.

But sometimes the threat stays. Sometimes the stimulus becomes permanent.

If I were to poke you in the stomach, you would flinch. No matter how much you exercised or how fit you were, your abdominal muscles would contract and your back muscles (the antagonists) would be inhibited.

If I then made that reaction permanent by leaving the irritation in place in the form of a belly piercing, then it would only be a matter of time before the back gave way in the form of a strain, sprain, pain, sciatica or disc bulge.

You can see the unsafe results of this safety mechanism in the following videos.

The first shows a young lady with 2 years of low back pain. As she stimulates the piercing, her low back inhibition vanishes (our body is more sensitive to changes in stimulation, than stimulation itself)

Belly piercing

In the second video a young dancer tells us what happened the day after she took her piercing out

Belly stud in a dancer

Whether or not a piercing induces inhibition is largely a matter of luck. It depends on which nerve endings are stimulated. It would appear that metal of all kinds is the worst nerve ending stimulator. Often if the piercing is replaced with nylon, teflon or wood, the inhibitory effect of the piercing is lost.

Foundation Module 1

Dental crowns affect proprioception and muscle strength

“Like a miracle”