Most people who run or walk and are relatively familiar with muscles in their bodies will have heard of their Gastrocs or |Gastrocnemius, the calf muscles that support the lower legs when pushing forwards or standing on their tip toes. However, mention the muscle Soleus and there is a quizzical look in the air! Perhaps it is the fact that it is hidden underneath the gastrocs and is out of sight ,out of mind.
The Soleus main function is to help you stand upright and constantly contracts to stop you falling forward, helping you keep your balance while walking, running and standing. When running, the soleus actually works harder than the gastrocs to maintain your balance and is usually the one that gets most sore when running , especially if you are a midfoot runner or converting to a midfoot strike. It has great endurance and fatigue qualities as it is made up of slow twitch fibres (prolonged muscle action) and is again constantly working while you are standing, running or moving around as opposed to the fast twitch fibres (fast muscle action) of the gastrocs. You can tell if your Soleus is tight by facing a bench, place the ball of your foot on the bench and bend your knee, then slowly dropping the heel. It is likely soleus if you feel achy stiffness.
Alternatively, if you stand facing wall and straighten out one leg behind you with heel on the ground its likely to be the gastrocs. Bringing the foot or ankle joint down and forward is the main function of the Soleus so runners who strain the soleus will find that movement painful or restricted.
The best way to recover or get mobility back in the soleus is to sit on a bench (or kitchen chair), bend up your knee, place a theraband on the balls of your feet and while holding the other end of the band start “pumping “ the ankle joint up and down slowly against resistance. 6 to 8 sets of 20reps once daily. Return to running also volume increases needs to be incremental especially if you are a midfoot runner. When exercising or strengthening the gastrocs always include the soleus muscle. It is the (Core) muscle of you lower limbs!