The soleus is a broad, flat muscle in the back of your lower leg that sits underneath the more visible calf muscle (the gastrocnemius). It runs from just below your knee down to your heel, and its primary job is pointing your foot downward, a motion called plantarflexion. What makes the soleus unusual is its role as a postural muscle: it works constantly, often without you noticing, to keep you from falling forward when you stand.
Where the Soleus Sits and How It Connects
The soleus originates from two bones in the lower leg. It attaches to the back of the fibula head (the smaller bone on the outside of your shin) and to the inner edge of the tibia (your shinbone), with a tendinous arch bridging the two attachment points. From there, the muscle fibers run downward and merge with the gastrocnemius to form the Achilles tendon, which inserts into the back of the heel bone.
Because it only crosses the ankle joint, the soleus is a single-joint muscle. The gastrocnemius, by contrast, crosses both the knee and the ankle. This distinction matters for how the two muscles are used: when your knee is bent, the gastrocnemius is shortened and less effective, so the soleus takes over as the dominant force pulling your heel upward. That’s why physical therapists test soleus function by having you point your foot while your knee is bent to 90 degrees.
Its Role in Standing and Walking
Every time you stand upright, your body’s center of gravity sits slightly in front of your ankles. Without constant correction, you’d tip forward. The soleus provides that correction, firing in small, sustained contractions to keep you balanced. This is why it’s sometimes called an “antigravity muscle.”
During walking and running, the soleus plays a critical role in the push-off phase of each step. It generates force to propel your body forward while also controlling how quickly your shin moves over your planted foot. In distance running especially, the soleus does a disproportionate share of the work compared to the gastrocnemius, which is better suited to explosive movements like jumping and sprinting.
A Unique Metabolic Profile
The soleus is composed primarily of slow-twitch muscle fibers, which are built for endurance rather than power. But research from the University of Houston has revealed something more interesting: when activated in a specific, sustained way, the soleus can raise its local oxidative metabolism (the rate at which it burns fuel) to high levels for hours, not just minutes. Most muscles can’t do this because they run through their stored glycogen and fatigue.
The soleus gets around this limitation because it relies less on glycogen than other muscles do, instead drawing more heavily on blood-borne fuels like glucose and fats. This means it can keep working without hitting the wall of glycogen depletion that limits other muscles. Researchers at the University of Houston developed a seated movement called the “soleus pushup,” designed to take advantage of this property. Early findings suggest that sustained soleus activation could improve how the body processes blood sugar and fat after meals, though the technique currently requires lab equipment to perform optimally, and practical instructions for everyday use are still being developed.
Soleus Strains vs. Other Calf Injuries
Soleus injuries tend to be overuse injuries rather than sudden tears. They’re especially common in distance and endurance runners, often developing from fatigue, overtraining, or prolonged running on hills where the knee stays bent. A gastrocnemius strain, on the other hand (sometimes called “tennis leg”), typically happens during a quick, explosive movement like a sprint start or a jump.
If you strain your soleus, you’ll likely feel pain when pressing on the Achilles tendon, when lifting your toes toward your shin, and when walking on tiptoe. The severity breaks down into three grades:
- Grade 1: Sharp pain at the start of activity that may fade as you continue, followed by tightness and aching afterward.
- Grade 2: Pain during activity that forces you to stop, with continued pain while walking, plus swelling and possible bruising.
- Grade 3: Severe pain, inability to bear weight or exercise, significant swelling and bruising.
One telltale sign that the injury involves the soleus rather than the gastrocnemius is when pain occurs with the knee bent. Since bending the knee takes the gastrocnemius out of the equation, pain during a bent-knee calf raise points to the deeper soleus.
Exercises That Target the Soleus
The key to isolating the soleus is bending your knee, which slackens the gastrocnemius and forces the soleus to do the work. The most common exercise is the seated calf raise: sit with your knees bent at roughly 90 degrees and raise your heels off the ground against resistance. Standing calf raises with straight legs, by contrast, emphasize the gastrocnemius.
For runners and athletes looking to prevent soleus injuries, strengthening this muscle in its working position matters. Exercises like wall sits with heel raises, or slow eccentric (lowering) calf raises with bent knees, build the kind of endurance capacity the soleus needs during long runs. Because soleus injuries stem from accumulated fatigue rather than a single bad step, building the muscle’s tolerance for sustained load is more protective than training for peak power.