Final answer:
The superficial peroneal nerve is stimulated to confirm an accessory peroneal nerve, which is associated with the muscles in the lateral compartment of the leg like the fibularis longus and fibularis brevis.
Step-by-step explanation:
When confirming an accessory peroneal nerve, we stimulate the superficial peroneal nerve. This is because the accessory peroneal nerve, if present, is typically a branch of the superficial peroneal nerve. This nerve primarily innervates the muscles in the lateral compartment of the leg, which includes the fibularis longus (peroneus longus) and fibularis brevis (peroneus brevis). These muscles are important for foot eversion and plantarflexion.