Which movement is primarily associated with the S1 nerve root?

Which movement is primarily associated with the S1 nerve root?

• A. Plantar flexion
• B. Dorsiflexion
• C. Great toe extension
• D. Knee extension

Answer: (A)

The S1 nerve root mainly controls plantar flexion of the foot. This movement is produced by the gastrocnemius-soleus complex, which is innervated by the tibial nerve with contributions from the S1 myotome. The Achilles reflex, a classic bedside test, is also primarily S1. In contrast, dorsiflexion is mainly governed by L4–L5 (tibialis anterior), great toe extension by L5 (extensor hallucis longus), and knee extension by L3–L4 (quadriceps). Therefore, plantar flexion best aligns with the S1 root.

The S1 nerve root mainly controls plantar flexion of the foot. This movement is produced by the gastrocnemius-soleus complex, which is innervated by the tibial nerve with contributions from the S1 myotome. The Achilles reflex, a classic bedside test, is also primarily S1. In contrast, dorsiflexion is mainly governed by L4–L5 (tibialis anterior), great toe extension by L5 (extensor hallucis longus), and knee extension by L3–L4 (quadriceps). Therefore, plantar flexion best aligns with the S1 root.