Achilles tendinopathy is one of the most common injuries affecting runners. Research suggests that up to 52% of middle and long-distance runners will experience Achilles tendinopathy at some point in their lifetime.
While that number may sound concerning, there is an important upside. When runners understand why this injury happens and how it develops, they can better manage their training and continue doing what they love most, which is running.
Understanding the signs, risk factors, and causes of Achilles tendinopathy can help runners make smarter decisions about training and recovery.
Where Achilles Tendon Pain Usually Occurs
Achilles tendinopathy typically presents as localized pain in the Achilles tendon, the large tendon connecting the calf muscles to the heel bone.
Many runners describe the pain by pinching the tendon between their thumb and finger to show exactly where it hurts.
There are generally two common locations where symptoms occur.
Insertional Achilles Tendinopathy
Pain occurs right where the Achilles tendon inserts into the heel bone, also known as the calcaneus.
Mid-portion Achilles Tendinopathy
Pain occurs slightly higher up the tendon, several centimeters above the heel.
If pain occurs along the entire length of the tendon, it may indicate a different condition and should be evaluated further.
Common Symptoms Runners Experience
Achilles tendinopathy often develops gradually and presents with several recognizable symptoms.
Pain with Loading
Pain is commonly felt during activities that place load on the tendon, particularly running and jumping.
The Warm-Up Effect
Many runners notice that the tendon feels painful or stiff at the beginning of a run, but as the run continues the discomfort may improve or feel easier. This is often referred to as the warm-up effect.
Morning Stiffness
Another common sign is stiffness first thing in the morning. Some runners may even feel difficulty placing their heel fully on the ground when they first wake up.
Reduced Performance
Runners may also experience difficulty pushing off the ground, which can affect running efficiency and performance.
It is important to remember that pain is information. The level of pain does not always reflect the extent of tissue damage in the tendon.
Why Achilles Tendinopathy Happens in Runners
Achilles tendinopathy is typically considered a load related or overuse injury. It often occurs following a change in training load.
Common training changes that can contribute include:
Increasing running volume
Increasing intensity or pace
Adding hill running
Reducing recovery time between sessions
One challenge for runners is that different systems in the body adapt at different speeds.
Aerobic fitness and muscles can adapt relatively quickly, often within four to six weeks of consistent training. However, tendons adapt more slowly, and meaningful changes in tendon stiffness may take closer to twelve weeks.
Because of this difference, runners may feel aerobically fit enough to increase training intensity while the tendon has not yet fully adapted to the new load.
The Role of the Achilles Tendon in Running
The Achilles tendon plays a critical role in running mechanics. It functions as an energy storage tendon and behaves much like a spring.
During running the tendon stores elastic energy when the foot contacts the ground and releases that energy during push off.
This occurs during what is known as the rapid stretch shortening cycle, where the tendon rapidly stretches and then recoils.
Running places significant forces through the Achilles tendon. Estimates suggest that each step can place approximately five to seven times a runner’s body weight through the tendon.
The tendon is strong and capable of tolerating these forces, but only when it has developed sufficient capacity to handle them.
Factors That Influence Achilles Tendon Load
When considering tendon load it is not just about the number of kilometers run. Several factors influence how much stress is placed on the Achilles tendon during training.
These include:
Running speed
Strides
Hill running
Running surface
Footwear characteristics such as heel drop and stiffness
Long runs and accumulated fatigue
Strides can be particularly demanding on the Achilles tendon. While they are effective for improving running economy and biomechanics, they place significant load on the tendon, especially when performed uphill.
Longer duration runs can also increase stress on the tendon due to fatigue.
In many cases Achilles tendinopathy develops due to a combination of multiple training factors along with lifestyle elements such as sleep, stress, and nutrition.
Two runs of the same distance can place very different levels of load on the tendon depending on these variables.
Risk Factors for Achilles Tendinopathy
Several factors may increase the likelihood of developing Achilles tendinopathy.
Previous Achilles Injury
The strongest risk factor is having experienced Achilles tendinopathy previously.
High Training Volume
Studies suggest runners training for longer events such as marathons may have a higher occurrence of Achilles tendinopathy compared with those preparing for shorter distances.
Reduced Calf Strength and Endurance
Weakness or fatigue in the calf muscles can contribute to increased stress on the tendon.
Certain Antibiotics
Some antibiotics have been associated with increased risk of tendon problems. Athletes taking new medications should discuss potential risks with a medical professional.
Why Some Observations Can Be Misleading
Some studies have observed higher odds of Achilles tendinopathy in runners who wear compression socks or follow a structured training plan.
However these findings may not indicate that these factors directly cause the injury.
For example runners often wear compression socks because they already feel a calf or Achilles issue developing. Similarly following a rigid training plan that does not account for sleep, stress, or recovery may increase injury risk if the program is not individualized.
Conditions That Can Mimic Achilles Tendinopathy
Pain in the back of the heel is not always caused by Achilles tendinopathy. Other conditions can produce similar symptoms.
These may include:
Paratenonitis
Retrocalcaneal bursitis
Haglund’s deformity
Sural nerve irritation
Plantaris tendon involvement
Calcaneal bone stress injury
If symptoms behave differently, for example if pain worsens with movement rather than improving, it may be important to seek professional evaluation.
Understanding the Bigger Picture
Achilles tendinopathy is a complex injury influenced by training load, recovery, strength, and overall health.
For runners the key takeaway is that training load must increase gradually so the tendon has time to adapt.
By understanding how the Achilles tendon works and what contributes to overload, runners can better manage their training and reduce their risk of injury while continuing to enjoy the sport.
