Illustration of an Achilles tendon thickening to reduce stress.

Achilles Tendon Woes? How Geometry Might Be Your Saving Grace

Reese Marlowe in Health & Wellness December 2025 • 4 min read.

"New research reveals that tendon thickening, often seen in Achilles tendinopathy, could be a beneficial adaptation to protect against stress."

Achilles tendinopathy, a common injury affecting athletes and non-athletes alike, is characterized by pain, stiffness, and impaired function of the Achilles tendon. It's a frustrating condition, and while various treatments exist, understanding the underlying mechanics of the injured tendon is crucial for effective management.

Traditionally, researchers have focused on the material properties of the tendon, noting that tendinopathy often leads to reduced stiffness and changes in tissue composition. However, emerging evidence suggests that the tendon's geometry – its unique shape and size – plays a more significant role than previously thought. This is especially intriguing because one of the hallmarks of Achilles tendinopathy is tendon thickening, where the cross-sectional area of the tendon increases.

A recent study published in the Journal of Biomechanics delves into this interplay between geometry and material properties, offering new insights into how the Achilles tendon adapts to tendinopathy. Using subject-specific finite element analysis, researchers investigated how altered geometry and material properties affect stress distribution within tendinopathic tendons compared to healthy ones. The findings challenge conventional wisdom and offer a reassuring perspective on the body's ability to compensate for injury.

Tendon Geometry: A Surprising Protector?

Illustration of an Achilles tendon thickening to reduce stress.

The study, led by Vickie B. Shim and colleagues, compared eight participants with Achilles tendinopathy to eight healthy controls. Using three-dimensional freehand ultrasound, they meticulously imaged the Achilles tendons of both groups at rest and during sub-maximal contractions. These images were then used to create detailed, subject-specific finite element models, allowing the researchers to analyze stress distribution within each individual's tendon.

The results revealed some fascinating insights:

Tendon Thickening: The resting cross-sectional area of the free tendon was, on average, 31% greater in the tendinopathic group compared to the healthy group. This confirms the well-established observation of tendon thickening in tendinopathy.
Reduced Stiffness: As expected, the Young's modulus (a measure of stiffness) was significantly lower (53%) in the tendinopathic tendons compared to the healthy ones. This indicates a reduction in the tendon's ability to resist deformation.
Lower Stress: Surprisingly, despite the reduced stiffness, the tendinopathic tendons experienced 24% less stress under the same sub-maximal loading conditions compared to the healthy tendons.

So, how can a stiffer tendon experience less stress? The key lies in the geometry. The researchers found that the increased cross-sectional area in the tendinopathic tendons had a greater influence on stress distribution than the reduced Young's modulus. In fact, the increased CSA alone reduced tendon stress by 30%, while the lower Young's modulus alone increased tendon stress by only 8%. This suggests that tendon thickening is a compensatory mechanism that protects the pathological tendon from excessive stress, despite its reduced stiffness.

Personalized Rehab: The Future of Tendon Care?

This study highlights the importance of considering individual tendon geometry in the management of Achilles tendinopathy. Generic rehabilitation exercises may not be optimal for all patients, as the stress experienced by the tendon will vary depending on its unique shape and size. Personalized training programs that account for individual tendon characteristics may be more effective in promoting positive tissue adaptation and preventing re-injury. By understanding the interplay between geometry and material properties, clinicians can better tailor interventions to optimize tendon health and function.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.jbiomech.2018.10.027, Alternate LINK

Title: Influence Of Altered Geometry And Material Properties On Tissue Stress Distribution Under Load In Tendinopathic Achilles Tendons – A Subject-Specific Finite Element Analysis

Subject: Rehabilitation

Journal: Journal of Biomechanics

Publisher: Elsevier BV

Authors: Vickie B. Shim, Wencke Hansen, Richard Newsham-West, Leila Nuri, Steven Obst, Claudio Pizzolato, David G. Lloyd, Rod S. Barrett

Published: 2019-01-01

Everything You Need To Know

What is Achilles tendinopathy, and how does it impact the Achilles tendon?

Achilles tendinopathy is a prevalent condition causing pain, stiffness, and impaired function in the Achilles tendon. The Achilles tendon, connecting the calf muscles to the heel bone, becomes inflamed and may undergo changes in its material properties, such as reduced stiffness, and its geometry, including tendon thickening. These changes affect the tendon's ability to withstand stress and perform its function of enabling movement like walking, running, and jumping.

How does the geometry of the Achilles tendon, specifically its cross-sectional area, influence stress distribution in the context of tendinopathy?

Research indicates that the Achilles tendon's geometry plays a crucial role in stress distribution. In Achilles tendinopathy, tendon thickening, an increase in the cross-sectional area (CSA), is often observed. This increased CSA acts as a compensatory mechanism, reducing the stress experienced by the tendon, even if the tendon's stiffness is reduced. The study showed that increased CSA alone reduced tendon stress significantly, suggesting that the tendon adapts its shape to protect itself from excessive stress.

What were the key findings of the study regarding tendon thickening, stiffness, and stress in Achilles tendinopathy compared to healthy tendons?

The study compared Achilles tendons with tendinopathy to healthy tendons, revealing significant differences. The tendinopathic group exhibited a 31% greater resting cross-sectional area, confirming tendon thickening. They also showed a 53% lower Young's modulus, indicating reduced stiffness. Surprisingly, despite reduced stiffness, the tendinopathic tendons experienced 24% less stress under sub-maximal loading. This lower stress was attributed to the increased cross-sectional area, highlighting the protective role of tendon thickening.

How can understanding the interplay between tendon geometry and material properties improve the management of Achilles tendinopathy?

Understanding the relationship between tendon geometry and material properties is key to personalized rehabilitation. Generic exercises may not be optimal because each person's Achilles tendon has a unique shape and size. By considering individual tendon characteristics, clinicians can tailor training programs to optimize tendon health and function. For example, exercises could be adjusted to account for the specific stress distribution within the tendon, promoting positive tissue adaptation and preventing re-injury. This personalized approach moves beyond solely considering material properties and embraces the importance of individual anatomy.

What are the implications of the study's findings for athletes and individuals experiencing Achilles tendon pain, and how should they approach their treatment and recovery?

The study's findings suggest that individuals with Achilles tendon pain should focus on personalized rehabilitation. Generic exercises may not be optimal because of the variation in tendon geometry. Athletes and other individuals should consult healthcare professionals who can assess their specific tendon characteristics, including cross-sectional area. Treatment should consider both material properties and geometry to tailor training programs, preventing further injury and promoting healing. This approach may involve exercises designed to manage stress distribution within the tendon and encourage positive tissue adaptation. Furthermore, this may also mean different exercises for different people. The focus should be on long-term tendon health and the prevention of re-injury through a customized approach.