Comprehensive Osteopathic Medical Licensing Examination (COMLEX USA) Practice

What is the primary action involved in the testing of S1?

1. Dorsiflexion of the foot

2. Plantar flexion of the foot

3. Flexion of the knee

4. Extension of the hip

The correct answer is: Plantar flexion of the foot

The primary action associated with the testing of S1 is plantar flexion of the foot. This action is primarily controlled by the muscles innervated by the S1 nerve root, particularly the gastrocnemius and soleus muscles, which are responsible for pointing the toes downward. In clinical practice, testing S1 may involve asking the patient to perform movements that engage these muscles, as their strength and functionality directly relate to the integrity of the S1 nerve root. Plantar flexion is essential for various functional activities, such as walking, running, and jumping, making it a key focus during neurological examinations of the lower extremities. Dorsiflexion, which involves lifting the foot upwards, is primarily controlled by the L4 and L5 nerve roots, not S1. Flexion of the knee and extension of the hip also do not primarily involve the S1 nerve root; they rely on different neurological pathways and muscle groups. Thus, recognizing the specific contributions of S1 to plantar flexion helps to understand the neurological evaluation of lower limb function effectively.