Motor Unit - What is a Motor Unit? Find Out!

Muscle Fibers
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What is a Motor Unit?

A motor unit is, of course, part of your muscles.  It's made up of a single motor nerve, which comes from the spinal core, and all the muscle fibers it stimulates.

Motor units actually come in different sizes.  For example, there are small motor units that may only stimulate 5 or 10 fibers, which would be things like blinking or moving your eye.

You also have motor units that are made up of up to 1,000 muscle fibers, which are responsible for big movements like kicking or jumping.

So, each time you do a squat jump, for example, you've got motor units firing all of those muscle fibers all at once, allowing you to move fast and furious.

How Do Motor Units Work?

As soon as a motor unit gets a signal from the brain, all of the muscle fibers in that unit contract at the same time with full force.  You can't go halfway with motor units - It's all or nothing when it comes to your muscle fibers contracting.  That means the amount of force you generate at any given time depends on how many motor units your body is calling for.

You can generate more force when you have bigger, stronger muscles, something that happens if you lift weights on a regular basis with a focus on overloading your muscles with more weight than they can handle.

As you challenge your muscles, they adapt by growing bigger and stronger in order to handle that added weight.

Weight Training Workouts

The key to getting stronger is, of course, to lift weights on a consistent basis.

  Here's where to start:


Source: American Council on Exercise. ACE Personal Trainer Manual, 3rd Edition. San Diego: American Council on Exercise, 2003.

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