The most commonly under trained muscle in runners is the soleus muscle. There are two muscles that make up our calves. One of them is the gastrocnemius and the other is the soleus. The gastroc muscle is larger and the one we can see and feel, where the soleus is a little smaller and sits behind the gastroc muscle. Both are powerful muscles that act to plantar flex the foot (point the toe downward) and are vital in running, walking, jumping, and keeping balance.
The soleus runs from just below your knee to your heel behind your leg, attaching at the top of the tibia and fibula leg bones (right at your knee joint) and inserting at the achilles tendon (by your heel). Predominantly a slow-twitch muscle, resistant to fatigue, it can be used for explosive movements as well. Injury to the soleus muscle is more common in older athletes and is often underestimated by all athletes.
What Makes it Important For Running?
When we run our body has to absorb and support up to 12x our body weight with each step. That’s a lot of load! While the soleus muscle doesn’t have the sprinting power that the gastroc does, it’s time to shine is in longer distance runs. The soleus bears the majority of the load during running in comparison to the gastrocnemius.
For runners the soleus:
The soleus propels us forward during running and walking
Bears most of the load from running
Is very resistant to fatigue
Tight Calf Muscles?
If the soleus is not strong enough to repetitively bear the load from running, the more we run the more likely the muscle is to fatigue causing the tightness that you feel. The tightness from fatigue is your body's way of sending a protective signal of stiffness or soreness to let you know. How do we fix it? We make it stronger!
How to Strengthen The Soleus:
In order to strengthen the soleus specifically, we have to take the gastrocnemius out of the mix. The way we do this is by performing bent knee (preferably at 90 degrees) exercises because the gastroc crosses the knee joint but the soleus does not. For example, adding bent knee calf raises to your exercises can help strengthen the soleus helping to prevent fatigue and tightness. If you don’t have access to a seated calf raise at your local gym, you can do these by sitting on a chair/bench, placing a dumbbell on your knee and doing a seated calf raise from there. Another option is to add calf raises into a wall sit where your knee is already bent at that 90 degrees.
Here is another great exercise that you can do to help strengthen your soleus and explanation for what it’s so important: