Tendon and superficial reflex arcs consist of a protective muscular contraction response to a stimulus. In the case of a tendon reflex the stimulus is a stretch to the tendon itself, whereas a superficial reflex is induced by stroking the skin.
To induce a tendon reflex, position the muscle so that it is on partial stretch to start with and gently strike the tendon with a neurological hammer, allowing it to swing as freely as possible so that it bounces off the fibres. In some cases the examiner places a finger over the target tendon, so that the tendon itself is not directly struck. The muscle should be observed for any resulting contraction.
The contraction is classified according to strength:
0 = absent
1 = reduced
2 = normal
3 = increased
4 = clonus (a repeated rhythmic contraction)
Reduced or absent reflexes may be associated with lower motor neuron lesions such as in peripheral neuropathy or nerve root lesions, or muscular disease. Increased reflexes or clonus may be associated with upper motor neuron lesions involving the spinal cord, brain stem or cortex.
Factors affecting reflex responses include the correct use of the hammer and location of contact. Patient tension and focus may interfere with the reflex response: consider using reinforcement techniques, or distracting conversation during tests.