A Systematic Review of the Effect of Exercise on Biomechanical Parameters of the Achilles Tendon

Background and Purpose
Achilles tendon injuries and dysfunctions, particularly Achilles tendinopathy, represent common issues among athletes and physically active individuals. The Achilles tendon, being the largest and strongest tendon in the human body, plays a critical role in locomotion by storing and releasing elastic energy during dynamic activities such as walking, running, and jumping. Given its high mechanical demands and vulnerability to overuse injuries, optimizing rehabilitation strategies for Achilles tendinopathy is essential. Exercise, particularly those involving mechanical loading, has emerged as a primary intervention. However, the precise effects of various exercise modalities and intensities on the tendon’s biomechanical properties remain a subject of ongoing investigation. This systematic review explores these impacts to guide evidence-based rehabilitation and prevention strategies. This study aims to systematically review the literature on how different forms and intensities of exercise influence the biomechanical parameters of the Achilles tendon, particularly stiffness, cross-sectional area (CSA), tendon elongation, and force transmission. The research also evaluates the effects of these exercise-induced changes on rehabilitation outcomes following Achilles tendinopathy.
 Methods & Materials
Following PRISMA guidelines, a comprehensive literature search was conducted across four major databases (PubMed, Scopus, Web of Science, and Google Scholar) for studies published between January 2020 and November 2023. Keywords included combinations of “Achilles tendon,” “exercise,” “stiffness,” “biomechanics,” and “rehabilitation” using Boolean operators (AND/OR). From an initial pool of 845 articles, 10 studies met the inclusion criteria after applying predefined filters related to language, methodology, relevance, and publication date. Studies involving amputation or cognitive disorders were excluded. All selected studies were independently evaluated by four reviewers using a standardized data extraction form and a modified MINORS scoring system for quality assessment.
 Results
Across the selected studies, various types of exercise interventions—ranging from short-term treadmill running to high-load resistance training—were found to significantly affect the mechanical and structural properties of the Achilles tendon. The results indicated that adequate external force application during exercise interventions is critical for improving tendinopathy outcomes. Significant correlations were observed between tendon stiffness, activity levels, and the Achilles Tendon Total Rupture Score (ATRS), highlighting the clinical relevance of stiffness and plantar pressure measurements. High-load interventions were found to induce significant mechanical and morphological adaptations in the plantar flexor muscle-tendon unit, potentially protecting the tendon from strain-induced damage. These findings suggest that high-load exercises can serve as an effective therapeutic protocol for Achilles tendon injury rehabilitation.
However, the review also revealed that stiffness measurements alone may not fully capture changes in Achilles tendon properties, emphasizing the importance of selecting appropriate evaluation methods during treatment and follow-up. The Achilles tendon is a dynamic tissue that adapts to mechanical loads, underscoring the need for tailored exercise and rehabilitation strategies.
 Discussion
This review emphasizes that the Achilles tendon is a dynamic, load-responsive tissue that adapts to exercise in a dose-dependent manner. Exercise interventions can modulate mechanical properties like stiffness and CSA, which are crucial for tendon resilience. High-load exercises, particularly those incorporating eccentric movements and maximal dorsiflexion, appear most effective in promoting tendon adaptation and rehabilitation. Nonetheless, the measurement of stiffness alone is insufficient to evaluate tendon health comprehensively.
Clinical outcomes are influenced not only by structural changes but also by neuromuscular coordination, proprioception, and metabolic efficiency. As such, multi-dimensional evaluation protocols—including biomechanical assessments, functional tests, and patient-reported outcome measures—should be integrated into tendon rehabilitation programs. Moreover, early intervention and tailored exercise protocols based on individual activity levels and injury history can enhance treatment efficacy and prevent recurrence.
Age-related changes also warrant consideration. With aging, tendon stiffness naturally declines, contributing to increased metabolic cost of walking and reduced gait efficiency. Rehabilitation strategies targeting the plantar flexor muscle–tendon unit in older adults may therefore need to incorporate both loading exercises and gait retraining using wearable biofeedback devices.
 Conclusion
The biomechanical properties of the Achilles tendon are modifiable through exercise, particularly when high mechanical loads are applied consistently over time. This systematic review demonstrates that exercise protocols focusing on tendon stiffness, CSA, and force transmission yield clinically significant improvements in tendinopathy rehabilitation. However, optimal assessment requires a comprehensive, multidimensional approach beyond stiffness measurement alone. Tailored rehabilitation strategies that consider patient-specific biomechanics, training history, and functional outcomes are essential for effective tendon recovery and injury prevention.
 Article Message
High-load, biomechanically informed exercise interventions can effectively improve Achilles tendon structure and function, serving as an optimal rehabilitation strategy for tendinopathy when integrated with comprehensive assessment methods.