If you have ever taken your shoes off after work and felt a dull, pressed-down ache along the inside of your foot, right where an arch is supposed to be, or noticed a pulling pain along the inner shin the day after a long walk, it may be worth considering whether flat feet (pes planus) are progressing. It is common for someone who has had flat feet since childhood without any symptoms to suddenly develop pain once body weight increases or activity levels rise. It is just as common to develop an adult-onset flatfoot later in life, as the tendons supporting the inner foot gradually weaken and the arch settles over time.
Flat feet are not just a matter of arch shape. Every time you walk, the foot rolls inward more than it should (overpronation), and that altered mechanic can ripple upward through ankle, knee, and even lower back alignment. In clinical practice, a large share of patients who come in complaining of flat-foot pain also mention inner knee pain or chronic low back fatigue.
Below, we will work through why flat feet develop and how they progress in stages, what to look for when choosing insoles and shoes, and a step-by-step self-care routine — including NIR LED care — that you can start at home today. Since physiologic flat feet in children and newly progressing flat feet in adults call for very different approaches, feel free to jump to whichever section matches your own or your family's situation.
Causes and Stages: Why Flat Feet Develop and Progress
What Is Flatfoot (Pes Planus): Causes and Stages of Progression
Flatfoot refers to a condition in which the medial longitudinal arch on the inside of the foot is lower than normal while standing, or collapses entirely so that the whole sole touches the ground. Although the term is often used loosely, clinically it splits into two quite different categories. Flexible flatfoot is one in which the arch appears normally while sitting or standing on the toes but disappears once weight is loaded onto the foot. Rigid flatfoot is one in which no arch appears in any position. Flexible flatfoot is usually closer to a physiological variation caused by generally looser ligaments, whereas rigid flatfoot is frequently caused by a structural problem such as tarsal coalition, in which bones are abnormally fused together — and the two require entirely different approaches.
Childhood Flat Feet and Adult Flat Feet Need to Be Viewed Differently
A study by Pfeiffer, Kotz, Ledl, Hauser, and Sluga, published in the pediatric journal Pediatrics (2006), photographed and analyzed footprints of about 835 preschool-aged children between three and six years old in Austria. The study found flatfoot findings in roughly 44% of the children overall, with the proportion decreasing as age increased. In other words, a large share of flat feet in young children reflects an arch that is still developing physiologically, and children who were heavier than their peers showed a markedly higher rate of flat feet, suggesting that body weight load can influence how the arch forms. Based on findings like this, pediatricians and orthopedists commonly recommend simply monitoring a child under roughly six to eight years old who shows flatfoot findings without any pain.
Newly developing or worsening flat feet in adults, however, is a different story. When the posterior tibial tendon, which runs beneath the inner ankle bone and effectively suspends the arch, weakens from repeated load or aging, the arch can gradually collapse into what is known as adult-acquired flatfoot deformity (AAFD). Obesity, metabolic conditions such as diabetes and hypertension that can affect blood flow to the tendon, ligament laxity from hormonal changes during pregnancy, and a notably higher tendency in women over 40 have all been reported as contributing factors.
Stages of Progression: The Johnson–Strom Classification
Adult flatfoot caused by posterior tibial tendon dysfunction is commonly evaluated in orthopedic practice using the staging system proposed by Johnson and Strom (1989), later refined with a fourth stage added by Myerson and colleagues. This classification is based on the extent of tendon damage and whether the foot deformity has become fixed.
| Stage | Tendon Status | Foot Shape | Management Direction |
|---|---|---|---|
| Stage 1 | Inflammation, normal length | Arch preserved, inner pain only | Rest, anti-inflammatory care, insoles, strengthening |
| Stage 2 | Tendon elongation / partial tear | Flexible arch collapse, still correctable | Custom insoles, bracing, strengthening exercise |
| Stage 3 | Tendon function lost | Fixed arch collapse, hard to correct | Orthopedic evaluation, bracing required |
| Stage 4 | Ankle joint involvement | Deformity extends to lateral ankle | Surgical correction consultation |
The higher the stage, the harder it becomes to reverse with self-care or wellness routines alone, so correcting shoes and insoles and starting tendon-strengthening exercise while still at stage 1 or 2 is far more advantageous in the long run.
Why Pain Can Spread to the Knees and Lower Back
A study by Menz, Dufour, Riskowski, Hillstrom, and Hannan using the Framingham cohort in the United States (Rheumatology, 2013) analyzed foot shape and the presence of low back pain in roughly 1,900 participants with an average age in their 60s. The study found that women with a pronated foot posture — one that rolls inward excessively — had a markedly higher likelihood of experiencing low back pain, while, interestingly, no statistically significant association was found among male participants. The researchers noted that the exact mechanism behind this sex difference requires further study, while suggesting that foot alignment may indirectly influence pelvic and spinal alignment. It would be a stretch to generalize from a single study, but if a woman with flat feet is also dealing with chronic low back fatigue, there is good reason to have her foot alignment checked.
The Connection to Shin Pain
A study by Yates and White conducted among U.S. Army basic trainees (American Journal of Sports Medicine, 2004) measured foot alignment in about 124 trainees before training began, then tracked who went on to develop medial tibial stress syndrome (commonly known as shin splints), pain running along the inner shin. Trainees with a larger navicular drop — a measure of how much the arch collapses under load, in other words a stronger tendency toward flat feet — showed a significantly higher rate of shin splints. This is frequently cited as evidence that the excessive pronation caused by flat feet does not stay confined to the foot, and can transmit repetitive traction stress up into the fascia surrounding the shin bone. That said, this study was conducted in a young, extremely high-activity population of trainees, so it would be a stretch to assume the same level of risk applies to adults whose activity consists mainly of everyday walking.
A Common Misconception: Does Flat Feet Always Mean Pain?
One of the most common misconceptions seen in clinical practice is treating flat feet and pain as if they were the same thing. In reality, plenty of people live their entire lives with flat feet and no pain at all, while others with arches in the normal range develop pain because of their shoes or activity habits. What determines whether pain shows up is not the height of the arch itself, but how well the tendons and muscles on the inside of the foot can handle that load. That is why the goal of management should not be to change the shape of the arch itself, but to build up the supportive capacity of those tendons and muscles while using shoes and insoles to redistribute the load.
Insole and Shoe Selection Criteria
Insole and Shoe Selection Criteria: How to Support the Arch
First, Check Your Own Flat-Foot Type
There is a simple check you can do at home before buying an insole. Wet the sole of your foot lightly, then step onto dry paper or a surface where a footprint will show, bearing full weight — this is known as the wet footprint test. If the inner portion of the footprint is almost entirely filled in, with little to no narrowing between the ball of the foot and the heel, flat feet are likely. If there is a distinct inward curve, the arch is likely closer to normal. Pairing this with a quick check of whether an arch appears when you rise onto your toes while barefoot can also give you a rough sense of whether you have a flexible flatfoot.
Insole Types at a Glance
| Insole Type | Support Level | Best Suited For |
|---|---|---|
| Off-the-shelf arch support (soft) | Low | Mild flexible flatfoot, preventive use |
| Off-the-shelf arch support (firm) | Moderate | Symptomatic flexible flatfoot |
| Semi-custom insole | Moderate-high | Foot width or arch height differing from standard |
| Fully custom insole | High | Stage 2+ adult-acquired flatfoot, structural deformity |
Shoe Selection Checklist
- Firm heel counter: Squeeze the heel cup of the shoe between your hands — if it does not collapse easily, it will better control the heel from tilting inward.
- Torsional resistance: Grip the shoe at the toe and heel and twist — a shoe that resists twisting provides better lateral support to the arch.
- Medial post: Motion-control shoes with a firmer midsole on the inner side than the outer help reduce overpronation.
- Room in the toe box: An arch-supporting insole adds volume inside the shoe, so choose a size with a bit more room than usual in the forefoot.
Do Insoles Actually Change the Way You Walk?
A study by Chen, Lou, Huang, and Su, published in the journal Clinical Biomechanics (2010) in Taiwan, fitted participants with flat feet with foot orthoses and analyzed the three-dimensional movement of the foot during walking. Wearing the orthoses was associated with a reduction in the degree to which the heel rolled inward right after landing (rearfoot eversion) compared with walking without them. This is often cited as evidence that insoles do more than simply redistribute pressure on the sole — they can partially influence the actual joint motion during gait. That said, the study involved a relatively small number of participants and only short-term observation, so the degree of benefit felt is likely to vary depending on an individual's own foot structure.
When a Custom Insole Becomes Worth Considering
If pain does not improve after four to six weeks of using an off-the-shelf arch support, if your foot width or arch height differs markedly from standard sizing, or if the arch has already collapsed and become fixed at stage 2 or beyond, it is reasonable to consider a fully custom insole molded from a cast of your own foot. Custom insoles cost more, but because they are built by precisely mapping where pressure concentrates, they frequently relieve pain that off-the-shelf products could not resolve. See also foot arch pain plantar fascia nir for how to tell this apart from plantar fascia pain.
Going Barefoot Isn't Something to Eliminate Entirely
Once people are fitted with insoles, many try to avoid ever taking them off, but the intrinsic muscles of the foot need some degree of barefoot stimulation to maintain their strength. A practical balance is to go without insoles at home on carpet or a padded floor, and wear them when you're out and will be standing or walking on hard surfaces for a long stretch. If you want to try barefoot walking outdoors, start on a soft surface like grass or sand for under ten minutes and gradually increase the time as your soles adapt, rather than jumping straight into longer sessions.
Self-Care Routine and NIR Care Protocol
A Self-Care Routine You Can Practice at Home
Why Build Up the Posterior Tibial Tendon and Intrinsic Foot Muscles Together
The core of managing flat-foot pain is not forcing the shape of the arch to change, but building up the supportive strength of the posterior tibial tendon that suspends the arch, along with the intrinsic muscles of the sole. In a randomized trial published in the journal Physical Therapy (2009), Kulig, Reischl, and colleagues compared a group of patients with early-stage posterior tibial tendon dysfunction who wore foot orthoses alone against a group who combined orthoses with resistance exercise. The group that added resistance exercise showed a greater improvement on a foot and ankle disability questionnaire (FADI), which is often cited as evidence that insoles alone are not enough — meaningful functional improvement requires strengthening exercise as well. That said, the study population was limited to adults with early-stage posterior tibial tendon dysfunction, so it would be a stretch to assume the same result applies equally to every case of flat feet.
Four Foundational Exercises
- Short foot exercise: Standing or seated barefoot, without curling the toes, draw the sole of the foot inward as if shortening the arch, holding for 5 seconds and repeating 10 times. It is common to feel almost no movement at first, but the sensation develops with repetition.
- Heel raise with slight eversion: Standing with feet shoulder-width apart, lift the heels while rotating them slightly outward to more actively engage the posterior tibial tendon. 10-15 reps, 2-3 sets.
- Towel scrunches: Lay a towel on the floor and scrunch it toward you with your toes 10-15 times to strengthen the intrinsic foot muscles.
- Calf stretch: Facing a wall, stretch for 30 seconds with the knee straight and 30 seconds with the knee slightly bent to build ankle and Achilles flexibility. Tight calves tend to place a greater burden on the arch during walking.
Sample Weekly Routine
| Day | Exercise | NIR Session |
|---|---|---|
| Mon / Wed / Fri | Short foot exercise + towel scrunches | 660+850nm, 10 min |
| Tue / Thu | Heel raise with eversion + calf stretch | 850nm, 10 min |
| Weekend | Light walking (20-30 min) then stretching | Optional (only if sore) |
Spend the first two weeks focused on learning the movements within a pain-free range, then gradually increase reps or sets from week three onward — this tends to be the easiest way to keep going without a setback. Missing a day does not mean starting over; simply pick up with the next day's routine.
Three Mistakes Almost Every Beginner Makes
Nearly everyone learning the short foot exercise for the first time trips up right here: mistaking a hard curl of the toes for the motion of lifting the arch. If your toes hook like claws, the form is off — the toes should stay flat while only the muscles on the inner sole draw the arch shorter. The second common mistake is pushing through a scheduled routine at full intensity even on a day when there is pain. If soreness lingers around the arch, cutting the reps in half or taking a day off will usually get you back on track faster in the long run. The third is wearing a newly fitted insole all day right from the start; the foot needs time to adapt to a new support angle, so it is safer to begin with just 2-3 hours a day for the first two to three days and extend wear time gradually from there.
NIR Wellness Application Protocol
| Phase | Wavelength | Target Area | Duration | Frequency |
|---|---|---|---|---|
| Acute (significant pain) | 660nm | Arch below inner ankle bone | 8-10 min | 1-2x/day |
| Subacute | 660+850nm | Arch + inner calf | 10-12 min | 1x/day |
| Maintenance | 850nm | Arch + calf | 10 min | 3-4x/week |
Application steps: wash the feet and let them dry completely. Position the arch beneath the inner ankle bone about 2-3cm from the device's light-emitting surface and irradiate for the duration shown above. Many users report it feels more comfortable to move directly into the short foot exercise or towel scrunches once the session is finished, while the tissue still feels warm and relaxed. That said, this is a subjective sensation tied to increased local warmth and blood flow, and it should be clearly understood that NIR itself does not have an established medical effect that reverses posterior tibial tendon dysfunction or arch collapse.
Thinking About the Load at 70kg Body Weight
If someone weighing 70kg (about 154lb) walks 8,000 steps a day, the inner arch and posterior tibial tendon must repeatedly absorb 1.2 to 1.5 times body weight with every single step. Even a rough calculation shows tens of thousands of kilograms of cumulative load across a day, so gaining even a few kilograms increases the burden on the arch by more than most people expect. This is exactly why insoles and exercise alone have their limits without also managing body weight. See also prolonged standing foot pain for related lifestyle adjustments.
Warning Signs and When to See a Doctor
Warning Signs and When to See a Doctor
In Children
- No arch appears even on tiptoe past around age 8, suggesting a possible rigid flatfoot.
- Pain or stiffness is markedly worse in one foot only (warrants ruling out a structural cause such as tarsal coalition).
- The child appears to actively avoid running or walking because of pain.
In Adults
- Sudden swelling and warmth below the inner ankle bone along with a visibly worsening arch collapse (suggests acute posterior tibial tendon injury).
- Doing a single-leg heel raise barefoot and the heel barely lifts, or lifts with marked wobbling.
- Pain does not improve, or worsens, despite eight or more weeks of consistent insole use and exercise.
- Reduced foot sensation from diabetes combined with recurring calluses or wounds alongside flat feet.
If any of these signs are present, a proper evaluation with X-ray, ultrasound, or MRI if needed should come first — self-care or a wellness device should not be used as a substitute. Adult-acquired flatfoot in particular tends to progress to stage 3 or 4 if left unaddressed, at which point bracing alone is no longer enough, so it is worth seeking care early even if the pain feels mild, once it has lasted more than a few weeks. See also heel pain plantar fasciitis care for help distinguishing related conditions.
When Conservative Care Isn't Enough: Considering Surgery
If bracing, strengthening exercise, and weight management have been tried consistently for six months or more without relief, and pain continues to limit daily walking or has progressed to stage 3 or beyond, an orthopedic surgeon may discuss surgical options such as a tendon transfer to reinforce the elongated posterior tibial tendon, or an osteotomy to realign the heel bone. Whether to proceed with surgery is generally decided based on the severity of pain and the degree of functional limitation, and even after surgery, continuing the tendon-strengthening exercises and shoe and insole management described above remains important for preventing recurrence.
Precautions When Using NIR
- Never irradiate the eyes directly; use protective goggles if needed.
- Consult your physician before use if you are taking photosensitizing medication (such as tetracyclines or certain acne medications).
- Do not irradiate areas with acute swelling, warmth, or open wounds.
- If sensation is reduced due to diabetes, keep distance and duration conservative to avoid the risk of burns.
- NIR is a wellness aid only, and it cannot replace professional medical care if pain persists or worsens.
Flat feet are, for most people, less an emergency to solve quickly than a chronic alignment issue managed gradually over months by changing shoes and insoles and steadily building tendon strength. Use the self-tests and checklists above to first figure out where your own feet currently stand, and do not hesitate to get a professional evaluation when needed — it is the surest way to protect not just your feet, but your knees and lower back as well.
