Despite differences in the anatomical and physiological characteristics of the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (Sol) muscles, it is common practice to investigate them as single triceps surae H-reflex recordings. The aim of this study was to compare the latencies of H-reflex recordings from the Sol, MG, and LG in patients with explicit magnetic resonance imaging (MRI) evidence of unilateral S1 radiculopathy and also compare their diagnostic yield in varied clinical characteristics (i.e., symptom duration and severity of involvement). We found a significant difference between H-reflex latencies of Sol and the two others (p < 0.05 for both comparisons). Although Sol had more sensitivity in patients with positive straight leg raising (SLR) of 30°-50° and also the sub-acute phase of the disease, and MG and LG had more sensitivity in the acute phase of the disease and patients with positive SLR of 50°-70°, there were no statistically significant differences between diagnostic ability of the three heads of the triceps surae in various clinical settings and they can be used interchangeably in patients with suspected S1 radiculopathies.