Not only is the soleus an important plantarflexor of the ankle, but it also functions as an important extensor and stabilizer of the knee.
When the foot is in contact with the ground, activation of the soleus results in closed-chain plantar flexion. This moves the superior aspect of the tibia (and attached knee) backwards, effectively extending (straightening) the knee. This function of the soleus is also important when landing from a jump, or when running, as it slows the knee moving forwards and reduces the load on the knee.
Those with weak quadriceps (recovering from an ACL or knee injury) may be able to use this function of the soleus as an alternative source of knee extension.
Following on from our previous video on calf strength and knee pain (view here), in the video below we show an example where a decrease in calf strength can increase knee load.
As explained above, during mid-stance in running, the soleus should eccentrically slow the forward movement of the shin, and if there is insufficient strength you can sometimes see an increased forward movement of the knee over the toes. This “knee over toes” can also be sometimes seen on landing from a jump or hop.
Remember, never assume the calves are weak, strength testing should be performed to confirm or disprove. Click here to find out more about assessing the strength of the calves.
Exercises that can help improve soleus strength include:
Seated calf raise
Double leg calf raises with knee bent, Single leg calf raises with knee bent
Box step down
Soleus wall sit
Rear leg elevated split squat