What symptom might be indicative of S1 nerve root compression?

Diminished ankle jerk is indicative of S1 nerve root compression because the S1 nerve roots are primarily responsible for the innervation of the gastrocnemius and soleus muscles, which are crucial for ankle plantarflexion. The ankle jerk reflex, or Achilles reflex, specifically tests the function of these muscles and the S1 nerve root. When compression occurs at this level, these muscles may not respond adequately, resulting in a diminished response during the ankle reflex test.

The other options, while they may involve different nerve roots or situations, do not directly correlate with the S1 nerve root function as clearly as the diminished ankle jerk. The knee jerk reflex is associated with the L2 and L3 nerve roots, lower back pain could stem from various conditions not specifically tied to S1, and paresthesia in the groin relates more to lumbar or sacral nerve issues rather than clearly indicating S1 compression. Thus, diminished ankle jerk serves as a direct and specific symptom of S1 nerve root involvement.