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A New Scale for Physical Therapists to Measure Muscle Tone

Posted on: 01/14/2010
If you've ever held an older infant, you know when placed in an upright position, they tend to bounce on their feet. That's a reflex. Pressure on the balls of the feet causes the ankles to plantar flex (toes point down). Eventually, the nervous system matures a bit more and this reflex is no longer so dominant. Now the child can put the foot down on the ground and walk without the plantar reflex causing bouncing.

This reflex seems to come back in adults who have had a cerebrovascular accident (CVA) (stroke). Damage to the brain from the stroke results in muscle hypertonicity (increased muscle tone). The increased tone and abnormal reflex reactions make walking normally difficult.

Physical therapists are often key members of the rehab team helping people with strokes to recover movement and function. Finding ways to reduce the excess tone and keep from triggering the plantar flexor reflex is an important part of the program. And in order to know if the treatment is working, it's necessary to measure the muscle tone and reflex response from before to after intervention.

Physical therapist researchers in Japan have been working on this problem for quite some time now. In previous studies, they examined the muscle hypertonia of patients after a stroke. They have used various measuring tools already available to evaluate speed and excitability of the ankle plantar flexor muscles. This group of muscles includes the gastrocnemius (large calf muscle) and the soleus muscle (a smaller muscle that forms part of the calf).

Now they present the results of another study using a new way to measure muscle tone of the ankle plantar flexor muscles. They developed this test themselves and call it the ankle plantar flexor tone scale. This new scale is meant to measure the quality of the plantar flexor muscle reaction when the (ankle) joint is passively moved (moved by the examiner rather than actively moved by the patient).

Any time a new testing method is developed, it must go through a rigorous examination to see if it is valid (does it really measure what it's designed to measure?) and reliable (does it consistently come up with the same results each time it's used?). They also checked the new test for intrarater reliability and interrater reliability. Intrarater reliability is the ability of one examiner to get the same results each time the test is administered to the same patient. Interrater reliability means the test will give the same results when given to the same patient by other examiners.

In this study, ankle flexor tone was measured using a handheld dynamometer, a device used to measure muscle force. All participating subjects were adults who had a diagnosis of cerebrovascular disease with hemiplegia. Hemiplegia means the stroke only affected one side of the body (usually both the arm and the leg).

To perform the test, patients were positioned supine (on their backs). The plantar flexor muscle force was measured during passive ankle motion using two velocities: as slow as possible and as fast as possible. The measurements were carried out using these two velocities in two separate positions: knee bent and knee straight.

After all the data was gathered and analyzed, they found that their test was, indeed, a valid and reliable way to measure ankle plantar flexor tone. And by comparing their test with other tests already available, they discovered that the Ankle Plantar Flexor Tone Scale gives more accurate and more complete information than the other tests.

Because this new test measures muscle resistance throughout the range of motion (beginning, middle, end), it can give the therapist additional information about the increased muscle tone present. Seeing the force of the stretch reflex and comparing it to the quality of muscle reaction helps the therapist. Now the therapist can identify when the problem is coming from changes in the brain (from the stroke) and when the exaggerated reflex is from local changes in the ankle muscle fibers and connective tissue.

The authors conclude that the greater detail provided by the Ankle Plantar Flexor Tone Scale will aid physical therapists when conducting research. The test will also provide an effective means of measuring changes in muscle tone for patients with neurologic conditions like stroke. Since muscle tone changes over time following a stroke and moving toward recovery, the scale might be able to offer another way of assessing progress and healing.

Nobuyuki Takeuchi, RPT, MS, et al. Development and Evaluation of a New Measure for Muscle Tone of Ankle Plantar Flexors: The Ankle Plantar Flexors Tone Scale. In Archives of Physical Medicine and Rehabilitation. December 2009. Vol. 90. No. 12. Pp. 2054-2061.

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