The soleus is located deep to the gastrocnemius and is the “workhorse” of plantarflexion.
See Images A and B below. It is a large muscle, flatter than the gastrocnemius, that is named for its resemblance to a sole – the flat fish that reclines on its side on the sea floor. The soleus has a continuous proximal attachment in the shape of an inverted U to the posterior aspects of the fibular and tibia and tendinous arch between them, the tendinous arch of soleus. See images below. The popliteal artery and tibial nerve exit the popliteal fossa by passing through its arch. See image C below.
Image A. Soleus anterior view
Image B. Soleus posterior perspective
Image C. Arteries and nerves
The soleus can be palpated on each side of the gastrocnemius when the individual is standing on their tiptoes (See image D).
The soleus may act with the gastrocnemius in plantarflexing the ankle joint; it cannot act on the knee joint and acts alone when the knee is flexed. Soleus has many parts (3) each with fibre bundles in different directions.
When the foot is planted, the soleus pulls posteriorly on the bones of the leg. This is important to standing because the line of gravity passes anterior to the leg’s bony axis. The soleus is thus an antigravity muscle (the predominant plantar flexor for standing and strolling), which contracts antagonistically but cooperatively (alternately) with the dorsiflexor muscles of the leg to maintain balance.
Composed largely of red, fatigue-resistant, slow-twitch (type 1) muscle fibres, it is a strong but relatively slow plantar flexor of the ankle joint, capable of sustained contraction. Electromyography (EMG) studies show that during symmetrical standing, the soleus is continuously active.
Manually stretching the soleus requires significant strength! Dorsi flexing the ankle is required, because its concentric action is plantar flexion.
Image E. Tabletop calf stretch
A tabletop stretch that we use in our StretchFit course and clinic is pictured below, image E. The difficulty with this stretch however is twofold.
First, when you eliminate the gastrocnemius from this stretch by bending the knee, it becomes difficult to perform and second, despite using leverage, the muscle is often very strong and tough to stretch in this position, particularly for the extended periods required (2 to 3 minutes.)
Image F. StretchFit Soleus Stretch
Because of the difficulty using the manual stretch, we often employ bodyweight or spring tension to do the work of stretching the soleus.
In image F, the knee is bent to slacken the gastrocnemius and to focus the stretch on soleus only.
Image G shows the combined gastrocnemius and soleus stretch. Of course, the 3 muscles of the deep posterior compartment are also stretched here.
Impingement can occur between the front of the lower tibia and a sulcus or depression on the talar neck, or on the talus itself. When compression occurs, its important to recognise that no further range of movement will occur. If you or your client still experiences a stretch at this point, the stretch can be continued if the compression sensation are not severe.
Why stretch the soleus?
Adequate flexibility is essential for the daily life movements of squatting, walking and running. When the calf muscles are tight for example, the foot must pronate in order to unlock the midtarsal joints to increase apparent (but not true) dorsiflexion. This excessive pronation can increase injury risk at the knee and foot.
A study in 1997 (molnar and Esterson) demonstrated that because of repetitive plantar flexion, 67% of elite ballet dancers lacked the normal 10% dorsi flexion required for normal walking gait. The follow up study reported leg injuries correlating significantly with those dancers with low dorsi flexion values. Injuries included plantar fasciitis, midfoot joint strain and Achilles tendinitis.
Important to keep in mind in ROM testing is that plantar flexion range is not just from the ankle joint. The contribution of the subtalar, midtarsal, and MTP joints is estimated to be between 10 and 40% of total plantar flexion range. So, we need to stretch the foot and its joints in its entirety! More on how to do that next time!
The stretches above are taken from the StretchFit combination station manual and from the book titled “Stretching on the Pilates Reformer, Essential Cues and Images,” available on Amazon books.