Posterior to the tibia bone are several muscles that collectively form the calf. As you can see in the illustration, there are six (6) muscles located posterior to the tibia. The three muscles identified by the letters j, k, l are nicknamed Tom, Dick, and Harry to represent the first letters of the three muscles (T=Tibialis Posterior, D=Flexor Digitorum Longus, H=Flexor Hallucis Longus).

Posterior Muscles	Soleus	Gastrocnemius

However, the gastrocnemius (a) and soleus (b) muscles form the bulk of the muscle mass and are typically referred to as the “calf” muscles. There is a small muscle named the plantaris (c) that is sandwiched in between the gastrocnemius and soleus muscles.

The gastrocnemius originates by two heads on the posterior lower femur just above the medial and lateral femoral condyles, thus crossing the knee as it runs toward its insertion point. The soleus originates on the upper posterior fibula and soleal line on the upper posterior tibia and does not cross the knee joint as it runs toward its insertion point. Both muscles pass posteriorly to the ankle joint for a common insertion on the posterior calcaneus via the Achilles tendon.

The Muscle Length-Tension Relationship

The potential strength of a muscle’s contraction is determined by the number of actin-myosin cross-bridges that form in the sarcomere during contraction. Therefore, to maximize the amount of force of a muscle’s concentric contraction, all actin-myosin bonding sites must be formed and involved. Typically, this is achieved when a muscle is slightly stretched.

To minimize the amount of force or active tension a muscle can produce when contracting, place “slack” in the muscle by reducing the amount of actin-myosin cross-bridges that participate in the contraction, officially referred to as shortened active insufficiency.

How to Isolate the Soleus Muscle from the Gastrocnemius Muscle

With an understanding of the muscle length-tension relationship, we can effectively isolate the soleus muscle for strenthening or stretching by placing “slack” or “shortend active insufficiency” in the gastrocnemius muscle.

To Isolate the Soleus Muscle For Strengthening

This is accomplished by placing the knee in a flexed position when performing ankle plantarflexion resistance traiining, such as performing reps of heel raises with a barbell across the distal thigh.

This places “slack” in the gastronemius muscle and reduces its involvement in performing ankle plantarflexion and places a greater challenge on the soleus muscles for a more effective and intense training.

Conversely, to place the greater challenge to the gastrocnemius muscle, perform planterflexion exercises (heel raises) against resistance with the knees extended. This places the gastrocnemius on stretch, maximizing its actin-myosin cross-bridges and ability to exert force for a greater workout.

To Isolate the Soleus Muscle For Stretching

Also, when stretching the soleus, flex the knee to place “slack” in the gastrocnemius muscle so that a greater stretch force is placed on the soleus. Leaning into the wall causes ankle dorsiflexion and stretches the soleus.

Conversely, to place a greater stretch to the gastrocnemius muscle (by increasing the distance between the origin and insertion of the muscle) keep the knee in an extended position when leaning forward against the wall.