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In a previous video, I described the concept of stabilizer muscles from a whole-body system
perspective, called global stabilizers, and I defined a type of stabilizer in specific
joint movements called fixators. You should see a link to that video appearing on your
screen right now. This video defines another type of stabilizer muscle in specific movements
called a neutralizer.
Neutralizers are similar to fixators in that they also act to prevent unwanted movement.
But, as you may recall, a fixator acts to prevent the unwanted movement of a body part.
A neutralizer, on the other hand, acts to prevent the unwanted line of pull from an
agonist or prime mover. Because of their arrangement, many muscles can produce a pulling force in
more than one direction. At the joint, this means that an undesired joint action might
occur along with the desired one. Basically, you want the joint to rotate in one particular
direction, but the muscle is actually pulling in more than one direction. Neutralizer muscles
can prevent this extra pull.
Like before, we'll use the familiar biceps brachii muscle. You may not be aware that
the biceps can actually do more than flex the elbow. It can also supinate the forearm.
That means that it can twist the forearm so that the palm faces up. Without some help,
what this means is that when you tried to bend your elbow, the biceps would also always
be turning your palm up at the same time. You don't always want this to happen, right?
It would make using a hammer impossible. And hammer curls wouldn't even exist. In order
for biceps action to flex the elbow without the forearm also being supinated, another
muscle must cancel out the supination torque that the biceps also produces. You have a
muscle on your forearm called the pronator teres. It is your main forearm pronator, meaning
it produces the opposite action of supination. This muscle counteracts the supination torque
of the biceps and so neutralizes this unwanted movement. Now, on the other hand, if you wanted
to supinate your hand, the biceps would also be involved in that. Now, you need a muscle
to cancel out the flexion role of the biceps, so you can turn your palm up without your
elbow tending to bend at the same time. Here, the triceps comes into play, neutralizing
the elbow flexion while the forearm is supinating. So, you can see that a muscle can have a different
role in different movements.
You can learn a whole lot more about the various roles of muscles by visiting the link in the
description below.