How can S1 nerve function be tested?

Testing S1 nerve function can be effectively conducted through the Achilles tendon reflex. This reflex is commonly assessed by tapping the Achilles tendon, located at the back of the ankle, while the patient's foot is slightly dorsiflexed. A response, indicated by plantar flexion of the foot, demonstrates that the S1 nerve root is functioning properly. The S1 nerve root is primarily responsible for the motor control of the calf muscles and for sensory innervation to the lateral aspect of the foot.

In contrast, the patellar tendon reflex evaluates the L4 nerve root, while the biceps and triceps reflexes assess biceps brachii and triceps brachii functions associated with C5-C6 and C7 nerve roots, respectively. Thus, these actions do not provide information regarding the S1 nerve function.