If you’re a runner with pain in the back of your heel or along the inside of your ankle, it’s unlikely that anything is structurally damaged. In most cases, the issue is a tendon that has been asked to handle more load than it is currently adapted for.
The two most common sources are the Achilles tendon and the tibialis posterior tendon. Both are designed to tolerate high forces during running. But both can become painful when training load increases faster than the tissue can adapt.
This does not mean something is broken. It means the tendon has reached its current capacity. When load goes beyond that capacity—through higher mileage, speed work, hills, or sudden changes in training—the tendon becomes irritated and sensitive. This is often most noticeable during running or after rest.
The key point is simple: this type of pain is usually a load problem, not damage. Because of that, the solution is not complete rest. It is learning how to adjust load so the tendon can gradually rebuild its capacity while you stay active.
Achilles tendinopathy in runners
The Achilles tendon is the strongest tendon in the body. During running, it absorbs forces of about four to eight times body weight with every step.
When it becomes irritated, pain is usually felt directly in the tendon. It is often tender to touch, painful with calf stretching, and aggravated by running or jumping. Morning stiffness is also very common. Some people notice thickening of the tendon over time.
Achilles tendinopathy is usually described as mid-portion or insertional, depending on where the pain is located. Mid-portion cases are more common in runners.
Many runners worry about rupture, but this is often misunderstood. A painful tendon is not “about to tear.” Most Achilles ruptures happen suddenly during high-force movements like sprinting or cutting. They are not the result of a slow progression of tendinopathy symptoms.
Tibialis posterior tendinopathy in runners
The tibialis posterior tendon runs behind the inner ankle bone. Its main role is supporting the arch of your foot during walking and running.
This condition often develops after a sudden increase in training load, such as a jump in mileage or intensity that the tendon is not prepared for. Pain is usually felt along the inside of the ankle and foot.
As it progresses, you may notice a flatter or more pronated foot posture. A key sign is difficulty performing a single-leg heel raise. In more severe cases, this movement may become very weak or not possible at all.
Having flatter feet does not mean you will develop this condition. The main driver is usually a sudden increase in load, not foot shape alone.
Why runners need to manage load, not just rest
Both Achilles and tibialis posterior tendinopathy come down to the same issue. The tendon is being asked to do more than it can currently handle.
Because of this, rest alone is rarely the answer. Long periods off running followed by a return to full mileage often leads to the same problem coming back.
A better approach is to adjust training variables such as running volume, speed, and frequency. This is combined with progressive strengthening work like calf raises and heel raise progressions.
The goal is to rebuild the tendon’s capacity so it can tolerate running again without repeated flare-ups.
What this means for your training plan
If you are currently dealing with this pain, complete rest without rebuilding capacity often just delays the problem. Once you return to normal training, symptoms tend to return.
A more effective approach keeps you moving within a tolerable range while gradually rebuilding strength. Running is reintroduced in a controlled way as the tendon adapts.
This process takes time. Usually weeks to months, not days. Progress depends on consistency, not speed.
When to get a proper evaluation
If you are unsure which tendon is involved, if symptoms are not improving with sensible changes to training, or if you have a history of ankle sprains or instability, a proper assessment can help clarify the problem and guide a more specific rehab plan.
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Dr. Jonny Blue is a Doctor of Physical Therapy and founder of Land and Sea Physical Therapy in Oceanside, CA. He specializes in orthopedic PT, root cause methodology, and helping active adults in North County San Diego get back to the activities they love without surgery or pain medication.