Plantar fasciitis develops when the thick band of tissue running along the bottom of your foot absorbs more stress than it can repair. That stress accumulates over time as tiny tears in the tissue’s collagen fibers, particularly where the band attaches to your heel bone. It affects roughly 1 in 120 adults in the United States and peaks between ages 40 and 60, though younger people who run or stand for long hours get it too. Understanding the specific forces and conditions that cause this damage helps explain why certain people are far more vulnerable than others.
What the Plantar Fascia Does
The plantar fascia is a flat, fibrous band that connects your heel bone to the base of your toes. Its job is structural: it stiffens the arch of your foot during movement, absorbs the impact of each step, and stores that energy so it can be converted into forward propulsion when you push off the ground. It works like a bowstring, maintaining the arch’s shape under load.
This tissue is especially active during two moments in every step. The first is right after your heel strikes the ground and your foot flattens to absorb impact. The second is when you push off your toes and the arch locks into a rigid lever. Both of these transitions put significant tension on the point where the fascia anchors to the heel bone. That anchor point is where the damage almost always begins.
The Core Mechanism: Overuse and Micro-Tearing
Plantar fasciitis is fundamentally an overuse injury. Each step sends your body weight and the ground’s reactive force straight through the fascia. Forces that compress or pull perpendicular to the collagen fibers are the most damaging, and those forces come primarily from two sources: your body weight pressing down and the ground pushing back up.
When those forces stay within normal limits and you get adequate rest between bouts of activity, the collagen fibers repair themselves. When the load exceeds what the tissue can handle, or when there isn’t enough recovery time, micro-tears accumulate faster than the body can fix them. The collagen at the heel attachment gradually degrades, thickens, and becomes painful. Notably, the central portion of the fascia is stiffer and less stretchy than the sides, which is likely why it’s the most injury-prone region.
The longer forces are applied continuously, the faster collagen breaks down. This is why prolonged standing and long-distance walking are such reliable triggers, not just intense bursts of activity.
Body Weight and BMI
Carrying extra weight is one of the strongest and most consistent risk factors. A study comparing people with and without heel pain found that the heel pain group had an average BMI of 30.4, compared to 28.2 in the pain-free group. That difference may seem small, but every extra pound adds cumulative load across thousands of daily steps. The researchers identified a BMI of 25 as a reasonable threshold below which the risk drops meaningfully.
This doesn’t mean only people who are overweight get plantar fasciitis. But if you’ve gained weight recently and started having heel pain, the connection is likely direct. The fascia simply isn’t designed to handle sustained increases in compressive force without consequences.
Foot Structure and Walking Patterns
The shape of your foot determines how force is distributed with every step, and certain structures put disproportionate strain on the fascia. Flat feet allow the arch to collapse too far inward during each step, overstretching the fascia at its heel attachment. High arches create the opposite problem: the fascia is pulled taut and rigid, leaving less flexibility to absorb shock. Both extremes concentrate stress in ways a moderate arch does not.
Unusual walking patterns matter too. If you pronate excessively (your foot rolls inward too far on impact), the fascia endures greater peak tension during the phases of your stride when it’s already working hardest. A leg-length discrepancy creates uneven force distribution between your two feet, and the longer leg typically bears more load. The body compensates with extra hip and knee flexion on that side, which further increases the tensile stress on the fascia. Plantar fasciitis from a leg-length difference almost always shows up in the longer limb first.
Jobs That Keep You on Your Feet
Occupational exposure is a major and sometimes overlooked cause. A study of assembly plant workers found that increasing time spent standing on hard surfaces, more time spent walking during shifts, and repeatedly getting in and out of vehicles (for forklift and truck drivers) all independently raised the risk. The hard surfaces matter because concrete and warehouse flooring don’t absorb impact the way softer ground does, so almost all of the ground reaction force passes directly into your feet.
Teachers, nurses, factory workers, retail employees, chefs, and construction workers are among the most commonly affected occupational groups. If your job requires standing or walking for most of the day, especially on hard flooring, the fascia is under near-continuous load with little opportunity to recover between shifts.
Running and Repetitive Exercise
Roughly 8% of foot injuries in runners are related to plantar fasciitis. Running and jumping amplify the same forces that damage the fascia during walking, but at much higher intensity. During running, the impact force at heel strike can reach two to three times your body weight, and the fascia absorbs a significant share of that energy.
Training errors are a common trigger: increasing mileage too quickly, running on hard surfaces like concrete, skipping rest days, or switching to minimalist shoes without a gradual transition. Hill work and speed intervals add even more tension because they demand greater push-off force. The issue isn’t running itself but the mismatch between the load you’re asking the fascia to handle and the recovery time you’re giving it.
How Footwear Contributes
Worn-out shoes are a surprisingly potent cause. As the sole and heel compress over months of use, the shoe loses its ability to absorb and spread ground reaction forces. More of that impact transfers directly into the fascia instead of being dissipated by the shoe’s cushioning. If you’re still running or working in shoes with hundreds of miles on them, you’ve effectively removed a layer of protection.
Several shoe characteristics affect fascia strain. A higher heel-to-toe drop (8 mm or more) shifts some of the workload to higher-leg muscles and away from the plantar fascia. A midsole that’s too soft creates an unstable platform where your foot wobbles, generating micro-movements that add stress to an already strained fascia. Shoes that twist easily when you wring them with your hands lack torsional rigidity, meaning they let your foot rotate during the stride rather than holding it steady. A firm heel counter that locks your heel in place adds stability and reduces the side-to-side movement that pulls on the fascia’s attachment point.
Flat shoes with no arch support, like flip-flops or ballet flats, offer essentially no shock absorption and let the arch collapse freely with each step.
Age and Tissue Changes
The peak incidence between ages 40 and 60 isn’t random. Collagen loses elasticity as you age, making the fascia stiffer and less able to absorb repetitive strain. The fat pad under the heel also thins over the decades, reducing your body’s natural cushioning. These changes mean the same activities that caused no problems at 25 can start damaging the fascia at 45, even if nothing else about your lifestyle has changed.
Heel Spurs Are Not the Cause
Many people with plantar fasciitis have a bony growth on their heel bone visible on X-ray, and it’s natural to assume the spur is causing the pain. It’s not. Heel spurs form as a result of long-standing tension at the fascia’s attachment point. They’re a consequence of the same chronic strain, not the source of it. Most people with heel spurs on imaging have no pain at all, and plantar fasciitis is treated successfully without ever removing the spur.
This distinction matters because it redirects attention to the actual problem: accumulated damage to the fascia’s collagen fibers from excessive, repetitive force. Addressing the load, the footwear, the body weight, or the foot mechanics is what resolves the condition, not dealing with the spur itself.