Inversion is the movement of turning your foot inward so the sole faces toward your other leg. Eversion is the opposite, turning your foot outward so the sole faces away from your body. These two movements happen primarily at the subtalar joint, which sits just below the ankle, and they play a central role in how your foot adapts to uneven ground, absorbs shock, and stays stable during walking.
How These Movements Work
When you invert your foot, the bottom of your foot angles inward. Picture standing on the outer edge of your foot. When you evert, the sole tilts outward, as if you’re standing on the inner edge. Both movements occur in the frontal plane, meaning your foot is tilting side to side rather than pointing up or down.
The joint responsible for most of this motion is the subtalar joint, where the heel bone (calcaneus) meets the ankle bone (talus). This joint acts like a hinge that lets your foot rock from side to side. The total side-to-side range of motion at the foot and ankle is roughly 35 degrees: about 23 degrees of inversion and 12 degrees of eversion. At the subtalar joint alone, the range is around 25 to 30 degrees of inversion and 5 to 10 degrees of eversion. Your foot naturally has much more inward range than outward range, which has important consequences for injury.
Muscles That Control Each Movement
Inversion is powered by muscles that run along the inner side of your lower leg. The main one is the tibialis posterior, a deep calf muscle whose tendon wraps behind the inner ankle bone and attaches to bones in the arch. It’s assisted by the tibialis anterior (the muscle you can see tense on the front of your shin when you pull your foot up and in), along with two deep toe-flexing muscles.
Eversion relies on muscles along the outer lower leg. The fibularis longus and fibularis brevis (also called the peroneal muscles) are the primary evertors. Their tendons run behind and below the outer ankle bone, pulling the foot outward when they contract. Two muscles on the front of the shin that extend the toes also contribute to eversion.
Why Your Foot Needs Both Movements
Every step you take involves a subtle cycle of inversion and eversion. When your heel strikes the ground, your foot typically everts slightly to absorb impact and adapt to the surface beneath it. As you push off for the next step, the foot inverts to create a rigid lever for propulsion. This constant toggling between a flexible, shock-absorbing foot and a stiff, push-off-ready foot is what makes walking on grass, gravel, or a cambered sidewalk feel natural without you having to think about it.
On uneven terrain the role becomes even more obvious. If you step on a rock or a root, the subtalar joint quickly adjusts through inversion and eversion to keep your ankle and knee aligned. When that adjustment happens too slowly, or the surface forces your foot beyond its normal range, a sprain can result.
Inversion vs. Eversion Ankle Sprains
Roughly 85% of all ankle sprains are lateral sprains caused by excessive inversion. The foot rolls inward too far and too fast, stretching or tearing the ligaments on the outside of the ankle. The most vulnerable is the anterior talofibular ligament (ATFL), which is the weakest of the three outer ankle ligaments and is injured in about 70% of lateral sprains, often on its own. With greater force, the calcaneofibular ligament tears next. The third outer ligament, the posterior talofibular ligament, almost never tears unless the ankle fully dislocates.
Eversion sprains are far less common because the ligament on the inner side of the ankle, called the deltoid ligament, is exceptionally strong. It takes significant force to damage it, and when it does tear, a fracture is often involved as well. This strength imbalance between the inner and outer ligaments explains why “rolling your ankle” almost always means rolling it inward.
Inversion and Eversion vs. Supination and Pronation
You’ll often see inversion grouped with supination and eversion grouped with pronation. The terms overlap but aren’t identical. Inversion and eversion describe a single-plane tilt of the foot, the side-to-side rocking at the subtalar joint. Supination and pronation describe more complex, three-dimensional motions that combine that tilt with rotation and up-or-down movement of the foot.
Inversion is one component of supination, which also includes the foot pointing slightly downward and rotating inward. Eversion is one component of pronation, which also includes the foot pulling slightly upward and rotating outward. In clinical practice, inversion and eversion tend to describe what a therapist sees when they manually move your foot while you’re sitting or lying down. Pronation and supination more often describe what your foot does during weight-bearing activities like walking or running. Both sets of terms trace back to the 19th century, and even among professionals, usage can vary, so context matters.
How Inversion and Eversion Are Tested
If you visit a physical therapist or orthopedic specialist after a foot or ankle injury, they’ll likely test both movements. For inversion, you’ll lie on your back with your ankle slightly pointed downward. The therapist stabilizes your lower leg just above the ankle and asks you to turn your foot “down and in.” They apply resistance against the inner edge of your forefoot, pushing it up and out, to see how much force you can resist. They may also feel for the tibialis posterior tendon just behind your inner ankle bone to confirm the muscle is firing.
Eversion testing follows a similar setup. Starting from a neutral ankle position, you’re asked to turn your foot “down and out.” The therapist pushes against the outer edge of your forefoot, directing force up and inward. Strength is graded on a 0-to-5 scale: 5 means you hold against maximum resistance, 3 means you complete the full motion but can’t resist any added force, and 0 means no detectable muscle contraction at all. Weakness in either direction can point to nerve damage, tendon problems, or lingering effects of a sprain.
Common Conditions Linked to These Movements
Beyond acute sprains, chronic imbalances in inversion and eversion contribute to several foot and ankle problems. Excessive inversion during walking or running can stress the outer ankle repeatedly, leading to chronic ankle instability, a condition where the ankle feels like it “gives way.” Weak evertors, particularly the peroneal muscles, are a common finding in people with recurring lateral sprains.
On the other side, excessive eversion (often described as overpronation in running communities) can strain the inner ankle, the arch, and the tibialis posterior tendon. Over time this may contribute to flat foot deformity, shin pain, or posterior tibial tendon dysfunction. Alignment issues higher up the leg can also show up as compensatory changes at the subtalar joint. Minor knock-knee or bowleg positioning in the lower leg can be partially offset by increased eversion or inversion at the foot, which is one reason a clinician may examine your subtalar motion even when your complaint is knee or hip pain.