Flat feet, known medically as pes planus, is a condition where the arch on the inside of your foot is flattened, allowing the sole to contact or nearly contact the ground when you stand. It affects roughly 5 to 14% of adults and is one of the most common foot variations in humans. For many people it causes no problems at all, but for others it can lead to foot pain and issues that ripple up through the knees, hips, and lower back.
How the Arch Works
Your foot’s inner arch is built from a chain of bones: the heel bone, the talus (which sits on top of it), the navicular, three small wedge-shaped bones in the midfoot, and the first three long bones leading to your toes. These bones don’t hold themselves up on their own. A network of ligaments, a thick band of tissue along the sole called the plantar fascia, and several muscles and tendons work together like cables on a suspension bridge to keep the arch lifted.
The most important of these cables is the posterior tibial tendon, which runs from your calf down behind your inner ankle and attaches to the bones in the middle of your foot. When this tendon contracts, it pulls the arch upward and locks the midfoot bones into a rigid lever for pushing off the ground. When it weakens or fails, the arch gradually collapses, and supporting ligaments stretch out over time.
Flat Feet in Children Are Usually Normal
All babies are born with flat feet. The arch develops gradually over the first decade of life, which is why a flat-footed toddler is not a cause for concern. Between 21 and 57% of children aged two to six have flat feet, a number that drops to roughly 13 to 28% in primary school children as the arch matures. The traditional clinical view is that a mature foot posture is reached somewhere between ages 7 and 10, though the exact timeline varies from child to child.
Because a flat foot is entirely normal at young ages, labeling it as a problem too early can lead to unnecessary treatment. In most cases, a child’s flat feet resolve on their own without any intervention.
What Causes Flat Feet in Adults
Some adults simply never developed a prominent arch during childhood, and their feet have always been flat. This is called flexible flatfoot: the arch disappears when standing but reappears when you sit down or rise onto your toes. It’s the most common type and often causes no symptoms.
Acquired flatfoot is a different story. It develops later in life, usually because the posterior tibial tendon degenerates. Without that tendon doing its job as the primary stabilizer of the arch, the surrounding ligaments and joint capsules gradually weaken, and the arch collapses. Risk factors for this tendon breakdown include obesity, high blood pressure, diabetes, and inflammatory joint conditions. Steroid injections near the tendon have also been linked to its deterioration. Injury, arthritis, and prolonged wear and tear can all contribute.
Symptoms Beyond the Feet
Flat feet don’t always hurt. Plenty of people live their entire lives with low arches and never have a single complaint. When symptoms do appear, they typically include pain or swelling along the inner ankle and arch, fatigue in the feet after standing or walking, and difficulty rising onto your toes on one foot.
The effects can extend well beyond the foot itself. When your arch is flattened, your foot tends to roll inward excessively with each step, a motion called overpronation. That extra inward rotation travels up your leg like a chain reaction, creating stress on the inner ligaments of the knee, altering hip alignment, and contributing to lower back pain. If you’ve been dealing with chronic knee or hip discomfort and can’t pinpoint the cause, your foot mechanics are worth examining.
How Flat Feet Are Diagnosed
A doctor or podiatrist can usually identify flat feet just by watching you stand and walk. Two simple clinical tests are commonly used. The first is the “too many toes” sign: when a clinician views your feet from behind, they’ll see more of your outer toes peeking out on the affected side than they should, because the foot has rotated outward. The second is the single-leg heel rise. You stand on one foot and try to rise up onto your toes. If the posterior tibial tendon is compromised, you either can’t do it or your heel fails to tilt inward the way it normally would. Imaging like X-rays may be ordered to assess the severity of the collapse and check for arthritis.
Exercises That Build Arch Support
Strengthening the small, deep muscles inside your foot is one of the most effective things you can do for flat feet. These intrinsic muscles act as a secondary support system for the arch, compensating for structural instability. Over-reliance on external support like rigid insoles without also strengthening these muscles can actually allow them to weaken further.
A few exercises are particularly useful:
- Arch lifts (foot doming): While standing with your feet flat on the floor, try to raise just the arch of your foot by rolling your weight to the outer edge, keeping your heel and toes planted. This targets the intrinsic foot muscles and has also shown benefits for plantar fasciitis.
- Marble pickups: Sit in a chair with 10 to 20 marbles on the floor next to a bowl. Use your toes to grab each marble and place it in the bowl. Picking up a towel with your toes provides a similar workout.
- Calf stretches and posterior tibial tendon exercises: Stretching your calf muscles reduces tension on the arch, while exercises that involve pointing and inverting your foot help strengthen the tendon most responsible for holding the arch up.
Consistency matters more than intensity. Doing these exercises daily, even for just 10 to 15 minutes, builds the muscular support your arch needs.
Orthotics and Arch Supports
Arch supports and orthotic insoles are among the most commonly prescribed treatments for flat feet, but the evidence behind them is surprisingly thin. A systematic review of studies on foot orthoses for adults with flatfoot found no firm conclusions could be drawn about whether they actually produce positive effects. The studies that do exist measured different outcomes using inconsistent methods, making results difficult to compare.
That said, many people report that prefabricated or custom-molded insoles reduce their day-to-day discomfort. They work by redistributing pressure across the sole and providing a mechanical cue that limits overpronation. If you want to try them, an inexpensive over-the-counter arch support is a reasonable starting point before investing in custom orthotics. The key is to pair any external support with the foot-strengthening exercises described above, so the muscles don’t atrophy from disuse.
When Surgery Becomes an Option
Surgery is reserved for flat feet that cause significant pain and haven’t responded to months of conservative treatment. The condition is staged based on severity, from stage I (pain and swelling along the tendon but normal alignment) through stage IV (a fixed, rigid deformity with the ankle joint itself tilting out of position). Early and mid-stage cases that remain flexible are treated with less invasive procedures, while rigid, advanced deformities require more extensive reconstruction.
Common procedures include shifting the heel bone inward to realign weight-bearing, lengthening the outer column of the foot to restore arch shape, transferring a neighboring tendon to take over the job of the failed posterior tibial tendon, and fusing specific joints to create stability in a rigid foot. Recovery typically involves a period of non-weight-bearing in a cast, followed by gradual return to activity over several months. The goal is to stop the deformity from progressing and reduce pain enough to return to normal daily function.