To examine the Achilles tendon reflex, the patient is first asked to lie in a supine or prone position with the knees flexed at about 90 degrees, or the patient is asked to kneel on the bed, then the examiner dorsiflexes the foot with the left hand and taps the patient’s Achilles tendon with a percussion hammer in the right hand. The reflex activity is mainly in the form of contraction of the gastrocnemius and hallux valgus muscles and flexion of the toes. If the patient’s lumbar disc herniates and compresses the patient’s sacral nerve, the patient’s Achilles tendon reflex may be weakened when examined.