What is Adaptive Shortening of Muscles?

Posted on 29 Aug 2012 14:06

A muscle can change its functional resting length to adapt to the length at which the muscle is habitually used or positioned.

An example of this type of muscle shortening is the shortening of the iliopsoas (one-joint hip flexors) in individuals who are confined to a wheelchair or who must spend most of their day sitting. Another example is the wearing of high-heeled shoes, which can cause adaptive shortening of the soleus since the foot must remain in plantar flexion. Adaptive shortening of muscles causes postural distortions which result in a further imbalance between opposing pairs of muscle.

Muscle Shortening Causes

Adaptive Shortening is muscle tightness caused by a muscle being forced to remain in a shortened position for a prolonged period of time, being unable to lengthen due to the relaxation of the antagonist group.

This shortness causes a slight to moderate decrease in muscle length and a restriction in range of motion. Gentle and gradually increased stretching can reverse the process in a matter of weeks, but care must be taken to avoid tearing of the muscle tissues.

The tightness caused by adaptive shortening should no be confused with tightness of hypertonicity due to interneuron dysfunction, since adaptive shortening is a pathologic process, and the muscle shows more resistance to lengthening, as both the contractile and mechanical properties of the muscle come into play. The shortened muscles are usually not painful at rest, but may be tender to touch, and easily irritated with movement. Over time, the normal contractile elements can be replaced with noncontractile tissue.

Postural distortions result in this adaptive shortening as well. For example, in the images below, misalignment of the neck causes adaptive shortening of the sternocleidomastoid muscle.

adaptive shortening of sternocleidomastoid

Shortened Sternocleidomastoid

Adaptive shortening causes what is known as a contracture. However, the shortened muscle is not the contracture itself. Instead, the term is usually applied to the joint whose range of motion the shortened muscle affects. For instance, tight hamstrings cause a limitation in the range of motion of knee extension. Since the hamstring is a flexor of the knee, this is called a knee flexion contracture.

As above, gentle stretching in the first line of defense against adaptive shortening. When possible, the habitual movements or positions that lead to the shortening should be eliminated. The earlier the intervention, the faster and better the results.

1. Kendall, Florence Peterson. Muscles, Testing and Function with Posture and Pain. Baltimore, MD: Lippincott Williams & Wilkins, 2005.
2. Hertling, Darlene, and Randolph M. Kessler. Management of Common Musculoskeletal Disorders: Physical Therapy Principles and Methods. Philadelphia: J.B. Lippincott, 1996. 153.

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This page created 29 Aug 2012 14:06
Last updated 09 Jan 2017 19:45

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