Achilles tendon reflex

The Achilles tendon reflex, also known as the ankle jerk reflex, occurs when the Achilles tendon is tapped while the foot is dorsi-flexed. A positive result would be the jerking of the foot towards its plantar surface.

The Achilles reflex checks if the S1 and S2 nerve roots are intact and could be indicative of sciatic nerve pathology. It is classically delayed in hypothyroidism. This reflex is usually absent in disk herniations at the L5-S1 level.