By Emily Swaim
Flat feet and plantar fasciitis are two feet conditions that can lead to a lot of heel pain. If you have flat feet, you are more likely to develop plantar fasciitis, and the pain in your heels is likely worse than for people with regular feet. Flat feet can also cause plantar fasciitis directly.
What are Flat Feet?
Up to 1 in 4 people globally have flat feet, also known as pes planus. If you are one of these people, the arches on your feet may flatten as you walk, or they may be flat all the time.
Flat feet generally aren’t a serious medical issue. Lots of flat-footed folks have no symptoms at all. But for some people, flat feet cause leg cramps and pain in their arch and heel. Flat feet can also change the way you walk, nudging the front of your foot outward.
What is Plantar Fasciitis?
Your plantar fascia is a fan-shaped group of fibers (fascia) along the sole of your foot (the plantar surface). They connect the bone in your heel with the bones at the front of your foot, almost like the string of a bow. When you step down, the tension in the plantar fascia helps your arch keep its curved shape.
Plantar fasciitis is inflammation (swelling) in your plantar fascia, causing stiffness and aching around your heel. You might feel the pain most when you take your first few steps in the morning. The pain could also get worse after exercise or a long shift working on your feet.
Can Flat Feet Cause Plantar Fasciitis?
A flat foot doesn’t roll through a step the way a normal foot does. The stiffer motion forces your plantar fascia to stretch beyond its limits.
This strain creates tiny tears in the connective fibers. Each time the fibers heal, your plantar fascia grows a little thicker and more rigid.
A stiffer plantar fascia can’t stretch or pull as easily as it should, so each step strains it even more. Eventually, the fibres get so damaged that they become painfully inflamed, giving you plantar fasciitis.
Can Plantar Fasciitis Cause Flat Feet?
Plantar fasciitis alone would not cause your foot’s arch to collapse. While your plantar fascia helps maintain your foot’s arch, it’s not the only support structure in your foot. Your posterior tibialis tendon (PTT) and spring ligaments do a lot more to preserve your arch’s integrity.
However, without functional plantar fascia, your arch may flatten more during your walk cycle. This flattening puts strain on your other connective tissues, making them more likely to tear. If multiple structures break, then you could develop a flat foot.
Shared Risk Factors
Flat feet and plantar fasciitis aren’t always connected through cause and effect. Sometimes they appear together due to a third, entirely different condition.
Your body mass index (BMI) measures how heavy you are given your height. Studies show people with higher BMI are more likely to have flat feet and plantar fasciitis.
That’s because when you step down, you put enough pressure on your foot to match 80% of your body weight. So if you weigh 200 pounds, your foot experiences 160 pounds of pressure. The more you weigh, the harder your feet work to carry you.
That said, a high BMI doesn’t always mean you are unhealthy or need to lose weight. Athletes can have dense muscle mass that gives them a higher-than-average BMI. The amount of weight on your feet matters more than whether they are carrying fat or muscle.
Decades of standing, walking, and running can gradually wear down the tissues in your feet.
When certain ligaments and tendons break, your arch collapses and flattens. This is called adult-acquired flatfoot deformity (AAFD). While AAFD isn’t an inevitable part of aging, it is fairly common. Older research suggests 1 in 10 adults over 65 have AAFD.
Meanwhile, most people who seek medical care for plantar fasciitis are of working age, between 25 and 65 years old. Working-age adults over 45 are over twice as likely to have plantar fasciitis as younger adults.
Posterior Tibialis Tendon (PTT) Dysfunction
Your posterior tibialis tendon (PTT) attaches the bones on the inside of your arch to the back of your leg. It’s one of the main structures holding your arch up. Damage to your PTT is by far the most common cause of AAFD.
PTT damage generally doesn’t cause plantar fasciitis directly. But if your PTT tears or breaks down, this can cause a chain reaction that overloads the other supportive structures in your foot. An older 2001 study looked at people with and without advanced PTT injuries. Nearly a third of the PTT-injured group had plantar fasciitis, compared to only 9% of the uninjured group.
How to Fix Plantar Fasciitis When You Have Flat Feet
According to a 2022 study, plantar fasciitis is often more painful if you have flat feet. These conditions can feed into each other, creating more damage and pain together than they could alone.
This is why rest is very important when you develop plantar fasciitis in flat feet. While you may not be able to stay off your feet 24/7, try to give your feet frequent breaks. If you need to blow off steam while you recover, consider doing low-impact exercises like swimming or cycling—these can get your blood pumping without exhausting your feet.
In addition to rest, you can also try gentle stretches and over-the-counter pain relievers. Insoles, orthotics, or supportive shoes can give your foot extra structure. If you have lasting pain, your doctor may recommend physical therapy or, in severe cases, surgery.