A patient with an S1 nerve root impingement would MOST likely have weakness performing which motion?

A patient with an S1 nerve root impingement is likely to experience weakness in plantar flexion. The S1 nerve root primarily innervates muscles responsible for plantar flexion, such as the gastrocnemius and soleus. These muscles are crucial for movements like standing on tiptoes, walking, and running. Impingement of the S1 nerve root can result in reduced strength or difficulty executing these movements, which directly affects the ability to perform plantar flexion effectively.

In understanding other functional abilities, hip extension is primarily associated with the gluteus maximus and is more influenced by the L5-S1-S2 nerve roots. Hip flexion is primarily controlled by the iliopsoas muscle, which is innervated by the L2-L3 nerve roots. Knee extension, powered by the quadriceps femoris muscle, is mainly innervated by the L3-L4 nerve roots. Therefore, while all these motions are critical for overall mobility and function, the specific weakness in this scenario is best identified in the context of plantar flexion due to the direct involvement of the S1 nerve root.