What type of muscle action does the soleus primarily perform?

The soleus is primarily responsible for plantar flexion, which is the movement of pointing the toes or elevating the heel. This action occurs at the ankle joint, where the soleus plays a crucial role, especially during activities such as walking, running, and standing on tiptoes.

Plantar flexion is essential for pushing the body forward in these movements, and the soleus works in conjunction with the gastrocnemius muscle to create the necessary force. This muscle action is vital for maintaining balance and stability when upright, as well as contributing to overall lower limb function during dynamic activities.

The other options do not accurately describe the function of the soleus, with adduction relating to moving a limb toward the midline, medial rotation concerning twisting a limb inward, and thigh extension involving the muscles of the hip rather than the calf muscles like the soleus.