A low arch foot, clinically called pes planus or flat foot, is a foot where the inner arch sits noticeably closer to the ground than normal or touches it entirely. Between 5% and 14% of adults have some degree of flat foot, making it one of the most common foot structure variations. For many people it causes no problems at all, but for others it leads to pain in the feet, ankles, knees, or even the hips.
How the Foot Arch Works
Your foot has three arches: a medial (inner) longitudinal arch, a lateral (outer) longitudinal arch, and a transverse arch running across the midfoot. When people talk about “the arch,” they almost always mean the medial longitudinal arch, the curved space along the inside of your foot between the heel and the ball. This arch is built from a chain of bones, including the heel bone, the talus (the bone that connects to your ankle), the navicular, three small wedge-shaped bones called cuneiforms, and the first three metatarsals. Tendons and ligaments hold these bones in their curved position and act like a bowstring under tension.
In a low arch foot, that curved structure partially or fully collapses. The result is a foot that makes broader contact with the ground, distributes force differently, and may roll inward more than it should during walking and running.
Flexible vs. Rigid Flat Feet
Not all low arches behave the same way. The distinction that matters most is whether your flat foot is flexible or rigid.
Flexible flat feet are far more common. If you sit down and look at your foot unloaded, you can see a visible arch. When you stand, the arch flattens. This is the type most children and many adults have, and it often causes little or no pain. Rigid flat feet are different: the arch is absent whether you’re standing or sitting, and you may have trouble flexing your foot up and down or side to side. Rigid flat feet are more likely to cause symptoms and may point to a structural problem in the bones or joints.
A Simple Way to Check Your Arch
You can get a rough sense of your arch height at home with what podiatrists call the wet test. Wet the sole of your foot, then step onto a piece of cardboard or a brown paper bag. Look at the footprint you leave behind. A flat foot prints nearly the entire sole, with little or no curve along the inside edge. A normal arch shows the heel and ball connected by a band along the outer foot, with a visible inward curve. A high arch leaves only the heel and ball with very little connecting them.
This test is a quick screening tool, not a diagnosis. If you’re having pain, a clinician can assess your arch with weight-bearing X-rays and a physical exam that differentiates flexible from rigid flat foot.
What Causes Low Arches
Many people are simply born with low arches. Flexible flat feet in children are extremely common and often persist into adulthood without causing trouble. Genetics, loose ligaments, and normal variation in bone shape all play a role.
When flat feet develop later in life, the condition is called adult-acquired flatfoot deformity. The most common culprit is gradual failure of the posterior tibial tendon, the tendon that runs behind the inner ankle bone and holds up the arch. Repetitive loading, degeneration over time, and sometimes acute injury wear this tendon down. As it weakens, the surrounding ligaments stretch, and the arch slowly collapses.
Several factors raise the risk. Obesity is one of the strongest: higher body weight increases the force on the tendon with every step, and studies consistently link elevated BMI to symptomatic flat feet. The typical patient who develops this condition is a woman in her 50s or 60s with excess body weight. Inflammatory conditions like rheumatoid arthritis, along with diabetes, high blood pressure, and long-term steroid use, can also accelerate tendon breakdown. Pregnancy can temporarily flatten the arches due to hormonal ligament loosening and weight gain, though the change sometimes becomes permanent.
How Low Arches Affect Your Body
When the arch drops, the foot tends to roll inward more than normal during each step. This is called overpronation, and its effects don’t stop at the ankle. The inward roll of the foot causes the shinbone to rotate inward, which pushes the knee into a knock-kneed position and rotates the hip inward. That chain reaction can alter pelvic alignment, reduce core stability, and contribute to pain at multiple points along the way.
Common symptoms linked to low arches include aching or fatigue along the inner foot and ankle, heel pain (often from plantar fasciitis, since the flattened arch places extra tension on the tissue along the sole), shin pain, and knee or lower-back discomfort. Some people develop bunions or hammertoes over time because the altered foot mechanics shift pressure onto joints that aren’t designed to handle it.
That said, plenty of people with low arches never experience any of these issues. Flat feet that are painless and don’t limit activity generally don’t require treatment.
Managing Low Arch Pain
When low arches do cause symptoms, treatment almost always starts with non-surgical options.
- Arch-supporting insoles or custom orthotics. Over-the-counter insoles with firm medial arch support can redistribute pressure and reduce the inward roll of the foot. Custom orthotics molded to your foot provide a more precise fit and are often recommended when off-the-shelf options don’t give enough relief.
- Supportive footwear. Shoes with a structured heel counter (the firm cup around the back of the shoe) and built-in arch support help stabilize the foot. Avoid completely flat shoes like flip-flops or worn-out sneakers, which let the arch collapse further.
- Targeted strengthening exercises. The posterior tibial muscle is the primary muscle supporting the arch. You can strengthen it with a resistance band: loop the band around the inside of your foot, anchor the other end to a sturdy object, then slowly point your foot downward and inward against the resistance. Control the return. Two to three sets of 10 to 20 repetitions, done consistently, can meaningfully improve arch control. A physical therapist can progress you toward weight-bearing exercises like single-leg heel raises and balance work that further train the arch under real-world conditions.
- Weight management. Because excess body weight directly increases the load on the arch-supporting tendon, even modest weight loss can reduce symptoms.
- Activity modification. Reducing high-impact activities temporarily while strengthening the foot can help calm an irritated tendon.
When Surgery Becomes an Option
Adult-acquired flatfoot deformity is classified in four stages. In stage I, there’s tendon pain and swelling but the foot alignment is still normal. Stage II involves a flexible deformity where the arch has dropped and the heel tilts outward, but the foot can still be manually corrected. Stage III is the same deformity but rigid, meaning it can no longer be repositioned by hand. Stage IV adds ankle joint involvement with the talus tilting inside the ankle.
Surgery is typically considered when the deformity has progressed beyond what bracing and physical therapy can manage, particularly in stages II through IV. Procedures range from tendon repair and bone realignment in earlier stages to joint fusion for rigid, advanced cases. Recovery is measured in months, not weeks, and often involves a period of non-weight-bearing followed by gradual rehabilitation. For most people, conservative treatment is effective enough that surgery never enters the conversation.