Unilateral (one-side-at-a-time) training allows you to restore left-right symmetry that may have strayed with constant bilateral work. When training both sides at the same time, it’s not uncommon for the stronger side to do most of the work. That applies to any bilateral exercise, including seated calf raises. I’m sure you’ve done seated calf raises many times in the past, but how often have you done them one leg at a time?
Just a reminder, your calves are composed of two main muscles: the gastrocnemius and the soleus. The gastrocnemius is a biarticular muscle that crosses two joints: the ankle and the knee. Its primary action is plantarflexion of the ankle when the knee is extended, thus the gastrocnemius is heavily activated during a standing calf raise. The soleus, however, is a uniarticular muscle crossing only the ankle joint and has greater involvement during a seated calf raise where the knee is bent at a 90-degree angle.
Sure, one-leg calf raises are popular, but they’re often done standing not seated. That’s great for the gastrocnemius, but to promote muscle balance between the left and right soleus, try doing seated one-leg calf raises. Don’t go too heavy. Maintain a controlled tempo, and pause at the top and bottom of the movement.