Why is the soleus muscle Important?
The deep, pancake-like soleus muscle inserts through the Achilles tendon on the heel. When your lower leg is bent at the knee, the soleus activates. This muscle is often called a “second heart” because of its ability to pump blood into the lower leg. If it is tight or lacks strength, it becomes like a dam inhibiting the flow of blood to your foot and ankle. The soleus doesn’t have the sprinting power that the outer calf has. It is the tortoise of the calf, containing more slow-twitch fibers, which makes it important for the long haul.
The soleus is the largest and strongest muscle in the calf. It gains its power from its complex configuration, attaching to its corresponding tendons at a 45-degree slant (called a multi-pennate structure) in multiple rows. The muscle starts at the top of the calf and attaches to the Achilles tendon at the bottom. It lies underneath the gastrocnemius muscle. These two structures are intimately connected, with some of their fibers overlapping. Some people consider them to be a single muscle, but their functions are different, and different tests are needed to check for injury of either structure.
It is imperative that the soleus muscle is able to slide independently of the gastrocnemius muscle. When these muscles become adhered muscle tension will develop, which can then put pressure on the muscular septum, which could lead to some called calf heart attack.
Pain from a soleus strain is felt deep in the calf, usually in the superior part, toward the knee. Discomfort can be felt in one spot or over a broad area because this injury can leave many fibers strained and inflamed.