The soleus stretch is designed to improve the flexibility of the soleus muscle.
Relevant anatomy: The soleus muscle and the gastrocnemius muscle are plantar flexors, which means they bend the foot back. The soleus acts to hold your leg firmly on your foot when you are standing. It arises from the posterior head of the fibula and down about a quarter of its shaft. Further on it arises from a fibrous band between the two bones and then along the soleal line on the tibia. Its fibers feed into a large tendon feeding in from above and both sides of the tendon. The tendon joins with the Achilles tendon or tendo calcaneous, the tendon for the gastrocnemius muscle lying superficial to the soleus muscle. The tendons join and insert on the calcaneous bone, the heel bone.
The calf muscle group is made up of Gastrocnemius and Soleus muscles. In general, stretches performed with the bend knee focus on the soleus muscle, while stretches done with knee straightened focus on the gastrocnemius muscle. The main function of the calf muscles is ankle plantarflexion however In addition to this the Gastrocnemius also acts to flex the knee when not weight bearing, and stabilizes the ankle and knee when standing.
The soleus muscle is composed primarily of type I muscle fibers (postural control) and the gastrocnemius is composed primarily of type II muscle fibers (power and mobility).Therefore the soleus gets shortened in individuals who have a history of standing for longer durations.
The two heads of the gastrocnemius and the soleus muscles together are known as the triceps surae and are the strongest plantar flexors of the ankle. Because the gastrocnemius and soleus muscles pass behind the ankle joint, a limitation in the length of the muscles results in limited dorsiflexion ROM. Furthermore, the gastrocnemius also passes behind the knee joint, and so shortness in the gastrocnemius may further limit dorsiflexion ROM when the knee is extended.
The following stretches help to stretch the soleus muscle in different body positions:
Soleus Stretch Standing
Ankle Dorsiflexion on a slant board
Ankle Dorsiflexion on a step unilateral
Ankle Dorsiflexion sitting with towel
Soleus stretch kneeling