The Role of Muscle Spindles


A muscle spindle is a small cluster of specialized muscle fibers within a muscle. Also called stretch receptors, they detect stretch (changes in the length) in the muscle.


  • The muscle spindle is a type of proprioceptor, which is a sensor in the muscle that identifies the location of your body parts. For example, If you close your eyes and move your arm, you still know where it's located because of proprioceptors.

What It Does

  • When a muscle stretches, the muscle spindle detects how much and how fast the muscle is stretching and sends signals to the spine with this information.

Stretch Reflex

  • If your body thinks a muscle is stretching too far or too fast, the muscle spindle's signals trigger the stretch or myotatic reflex. The stretch reflex resists further stretching of the muscle by causing the muscle to contract.

Static and Dynamic

  • The stretch reflex has two components. The dynamic component lasts for only a moment in response to the initial sudden increase in muscle length. The static component lasts as long as the muscle is being stretched.


  • The purpose of muscle spindles and the stretch reflex is to help maintain muscle tone and to protect your body from injury caused by overstretching.

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  • Photo Credit "Practice Makes Perfect (ii)" is Copyrighted by Flickr user: Lin Pernille ♥ Photography (Lin Kristensen) under the Creative Commons Attribution license.
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