Foundational Principles and Adaptation of the Healthy and Pathological Achilles Tendon in Response to Resistance Exercise: A Narrative Review and Clinical Implications

Abstract

Therapeutic exercise is widely considered a first line fundamental treatment option for managing tendinopathies. As the Achilles tendon is critical for locomotion, chronic Achilles tendinopathy can have a substantial impact on an individual’s ability to work and on their participation in physical activity or sport and overall quality of life. The recalcitrant nature of Achilles tendinopathy coupled with substantial variation in clinician-prescribed therapeutic exercises may contribute to suboptimal outcomes. Further, loading the Achilles tendon with sufficiently high loads to elicit positive tendon adaptation (and therefore promote symptom alleviation) is challenging, and few works have explored tissue loading optimization for individuals with tendinopathy. The mechanism of therapeutic benefit that exercise therapy exerts on Achilles tendinopathy is also a subject of ongoing debate. Resultingly, many factors that may contribute to an optimal therapeutic exercise protocol for Achilles tendinopathy are not well described. The aim of this narrative review is to explore the principles of tendon remodeling under resistance-based exercise in both healthy and pathologic tissues, and to review the biomechanical principles of Achilles tendon loading mechanics which may impact an optimized therapeutic exercise prescription for Achilles tendinopathy.

Current practice, guideline adherence, and barriers to implementation for Achilles tendinopathy rehabilitation: a survey of physical therapists and people with Achilles tendinopathy

“…There is wide variability in the application of therapeutic exercise for lower limb tendinopathies 33. Intervention studies guiding AT rehabilitation through therapeutic exercise can be generally classified into two groups: (1) comparative studies conducted in clinical settings of people with AT which often conclude that therapeutic exercise improves symptoms; or (2) studies of healthy tendon adaptation which may not be generalisable to pathological tendons 34. Several evidence-based therapeutic exercise interventions exist for AT management,35 with no optimal programme emerging 34 36 37…”

“…Similarly, while many different types of exercises are used when managing AT, eccentric exercises were the most popular, perhaps also due to the relatively large number of studies which have used this approach 33. The finding that therapists employ a variety of exercise types implies that the specific type of exercise or use of a specific programme is considered less important than individual tailoring and engagement with the programme 34 39. Despite CPG recommendations and the recognised utility of the VISA-A40 and the FAAM,41 few PTs reported using them.…”

“…Innovative programming coupled with ongoing patient education may help target patient and PT identified barriers such as programme time commitment, access to space/exercise equipment, and the belief that exercise as an AT treatment strategy is ineffective. With no optimal therapeutic exercise programme currently existing,34 36 37 PTs and researchers have an opportunity to improve AT management by using novel tools, technologies, and strategies to promote patient engagement with therapeutic exercise. Given the high acceptability of mobile applications within clinical practice by both PTs and people with AT (online supplemental file 5), applications may provide one avenue forward in addressing barriers and enhancing the facilitators identified in this study.…”

“… 34 Several evidence-based therapeutic exercise interventions exist for AT management, 35 with no optimal programme emerging. 34 36 37 …”

Type Synthesis of a Novel 4‐Degrees‐of‐Freedom Parallel Bipedal Mechanism for Walking Robot

“…Because the Achilles tendon is composed of mechanically sensitive tendon cells, it can temporarily store and release large amounts of energy during human walking, thereby reducing the impact of the ground and increasing walking efficiency. [ 62 ] Inspired by the structure of the human lower‐limb skeletal muscles, especially the knee joint and Achilles tendon, we designed the knee joint using a crossed four‐link mechanism with a variable instantaneous center of rotation and used a spring accumulator to simulate the Achilles tendon, as shown in Figure . The ACL linkage in the knee joint is connected to the posterior femoral linkage at the upper end and the tibial linkage at the lower end.…”