Effect of Foot Position During Rehabilitation of Achilles Tendinopathy on Tendon Mechanics and Symptoms.

Overview

This study will investigate whether a 12-week load-based exercise program performed with an externally rotated foot position ("toes-out") leads to different changes in intra-tendinous sliding, symptoms, and function compared to a standard exercise program performed with a neutral foot position in individuals with mid-portion Achilles tendinopathy. In addition, physical activity will be monitored during and after the intervention to examine how daily loading patterns relate to symptoms and functional recovery over a 6-month period.

Achilles tendinopathy is a common overuse disorder characterized by pain, swelling, and impaired function, with substantial impact on sports participation and quality of life. Despite exercise therapy being considered the gold standard treatment, rehabilitation outcomes remain suboptimal, with a considerable proportion of patients reporting persistent symptoms and many failing to return to their preferred level of sport. This highlights the need to improve current rehabilitation strategies and better understand mechanisms underlying tendon recovery. The Achilles tendon is mechanically complex, as it is loaded by the triceps surae muscle group and can be considered to consist of three partially independent subtendons that slide relative to each other. This intra-tendinous sliding has been investigated during passive and active loading tasks and may represent an important feature of healthy tendon behavior. It has been proposed that sliding may help distribute stress within the tendon and may contribute to tendon adaptation through local shear-related mechanobiological responses. Emerging evidence suggests that intra-tendinous sliding is altered in tendinopathy. Previous work has demonstrated reduced sliding in pathological tendons compared to healthy controls, while external foot rotation ("toes-out") has been shown to increase sliding during isometric and dynamic loading tasks. These findings raise the possibility that modifying foot position during rehabilitation exercises may influence internal tendon loading and promote more favorable adaptations. However, no studies have investigated changes in intra-tendinous sliding longitudinally during an exercise therapy program or whether modifying foot position during rehabilitation affects clinical outcomes. This study will therefore compare two 12-week load-based rehabilitation programs for individuals with mid-portion Achilles tendinopathy: a standard program performed with a neutral foot position and an adapted program performed with an externally rotated foot position. The study will investigate whether these interventions lead to different changes in intra-tendinous sliding, tendon morphology, symptoms, and functional recovery. In addition to the prescribed exercise intervention, the study will investigate the role of daily physical activity in rehabilitation outcomes. Tendon loading occurs not only during structured exercise therapy but also through habitual and sport-related activity, which may influence recovery. However, little is currently known about how physical activity patterns change during and after rehabilitation or how these patterns relate to symptoms and function. Physical activity will therefore be monitored throughout the intervention and follow-up period to evaluate changes in activity behavior over time and to explore associations between daily loading patterns, symptom progression, and functional outcomes. By combining evaluation of tendon-specific mechanical adaptations with monitoring of physical activity behavior, this study aims to provide new insights into factors influencing recovery in Achilles tendinopathy and to inform optimization of rehabilitation strategies.