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The biceps jerk is tested by placing one finger on the biceps tendon and then tapping it with a tendon hammer. The hammer should not be wielded, and instead should allowed to fall with gravity on the positioned finger.
If the reflex is intact then there is a brisk contraction of the belly of biceps, and consequent flexion of the elbow, followed quickly by relaxation.
If the reflex is absent then ask the patient to clench their teeth - a form of reinforcement - and test for the reflex again.
An increased reflex occurs in upper motor neurone lesion.