Which of the following is an expected sacral S1-S2 muscle function?

• A. Ankle plantarflexion
• B. Knee extension
• C. Hip adduction
• D. Toe extension

Answer: (A)

Ankle plantarflexion is the function most tied to sacral S1–S2. The muscles doing plantarflexion, mainly the gastrocnemius and soleus, are innervated by the tibial nerve, which receives strong contribution from those sacral roots. This movement powers the push-off in walking and standing on tiptoes, so weakness here points to sacral S1–S2 involvement.

Knee extension, on the other hand, is driven mostly by the quadriceps via the femoral nerve (L3–L4). Hip adduction relies on the obturator nerve (L2–L4). Toe extension is predominantly supplied by nerves involving L5–S1, not primarily S1–S2. So the plantarflexion movement best reflects sacral S1–S2 function.