Which nerve root is tested by the peroneus longus and peroneus brevis muscles?

• A. L5
• B. S1
• C. S2
• D. L4

Answer: (B)

The key idea is linking a muscle’s action to the nerve that supplies it and then to the nerve roots that contribute to that nerve. Peroneus longus and peroneus brevis are the foot everters, and they receive innervation from the superficial fibular (peroneal) nerve. The fibers most relevant for testing this muscle group come from the S1 nerve root. So when you test eversion strength against resistance, you’re assessing the function of the superficial fibular nerve and its S1 contribution. If eversion is weak, it points to S1 involvement or to a problem with the superficial fibular nerve, whereas other roots (like L4 or L5) would more prominently affect dorsiflexion or inversion rather than eversion.