Motor Function Basic Principles

The motor system is evaluated for the following:

• Muscle strength Muscle tone

The motor examination begins with inspection of each area being tested. The contours of symmetric muscle masses in both the upper and lower extremities are compared. Inspection is used to detect muscle atrophy and the presence of fasciculations.

Test muscle strength by having the patient move actively against your resistance. Compare one side with the other. The following is an arbitrary scale that is commonly used for the grading of muscle strength:



No contraction detected



Slight contraction detected



Movement with gravity eliminated (sideways)



Movement against gravity (upward)



Movement against gravity with some resistance


Normal: Movement against gravity with full resistance

If muscle weakness is found, compare the proximal and distal strengths. In general, proximal weakness is related to muscle disease;distal weakness is related to neurologic disease.

Tone can be defined as the slight residual tension in a voluntarily relaxed muscle. Tone is assessed by resistance to passive movement. Ask the patient to relax. Perform passive motion of the muscle. Compare one side with the other. Upper motor neuron lesions produce spasticity,* hyperreflexia, clonus,{ and Babinski's sign.{ Lower motor neuron lesions produce atrophy,

*An increase in muscle tone that results in continuous resistance to stretching. Spasticity is usually worse at extremes of range.

{Spasm in which rigidity and relaxation alternate in rapid succession. {Dorsiflexion of the big toe on stimulation of the sole of the foot.

fasciculations, decreased tone, and hyporeflexia. Both types of lesions result in weakness. Fasciculations may become more apparent by gently tapping the muscle with a reflex hammer.

It is impractical to test all muscles during the neurologic examination. By testing key muscle groups, the examiner can determine whether a gross deficit exists. Further testing of specific muscles and nerve roots may then be necessary. The student is referred to the many textbooks on neurology for these detailed examinations.

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