Structure-function Specialisation of the Interfascicular Matrix in the Human Achilles Tendon

Abstract

Objective Tendon consists of highly aligned collagen-rich fascicles surrounded by interfascicular matrix (IFM). Some tendons act as energy stores to improve locomotion efficiency; these tendons are prone to debilitating injuries, the incidence of which increases with ageing. In equine tendons, energy storage is achieved primarily through specialisation of the IFM. However, no studies have investigated IFM structure-function specialisation in human tendons. Here, we compare the positional anterior tibialis and energy storing Achilles tendons, testing the hypothesis that the Achilles IFM has specialised composition and mechanical properties, which are lost with ageing. Methods We used a multidisciplinary combination of mechanical testing, immunolocalisation and proteomics to investigate structure-function specialisations in functionally distinct human tendons and how these are altered with ageing. Results The IFM in the energy storing Achilles tendon is more elastic and fatigue resistant than the IFM in the positional anterior tibialis tendon, with a trend towards decreased fatigue resistance with age in the Achilles IFM. With ageing, alterations occur predominantly to the proteome of the Achilles IFM. Conclusion The Achilles tendon IFM is specialised for energy storage, and changes to its proteome with ageing are likely responsible for the observed trends towards decreased fatigue resistance. Knowledge of key energy storing specialisations and their changes with ageing offers insight towards developing effective treatments for tendinopathy.

The impact of age-related increase in passive muscle stiffness on simulated upper limb reaching

“…Moreover, the increase in passive force could occur with, and be partially caused by, age-related reduction in optimal muscle lengths [29]. Tendons, which affect force transmission and a muscle’s length and velocity trajectory during movements, may also undergo age-related structural changes [57], although the changes in tendon stiffness can be insignificant in the upper limbs [58]. Due to the nonlinearity of the arm model, the consequences of multiple such changes are hard to predict, and hence remain a subject for further study.…”

Tendon healing: a concise review on cellular and molecular mechanisms with a particular focus on the Achilles tendon

“…19 Nevertheless, the interfascicular ECM in the AT plays an important role in mediating isoelastic properties and, hence, biomechanics of this tendon. 20 Tendon is a hypocellular tissue consisting mainly of the ECM. 21 The ECM contains large amounts of collagen (mainly of type 1, 70% of dry weight), 22 elastic fibres, few proteoglycans (at least 1% of dry weight), 23 and various glycoproteins such as tenomodulin (TNMD) and tenascin C. 24 The composition of the ECM differs between the midportion and enthesis parts (the latter is mostly fibrocartilaginous) of the AT.…”

Predictive Ability of Achilles Tendon Elastography for Frailty in Older Adults

“…Aging-related changes in AT stiffness may lead to decreased resistance during movement, affecting walking performance and balance, crucial for maintaining mobility and physical function [12]. Since elastic tendons transfer muscle forces to skeletal bones, it's been proposed that changes in tendon properties also contribute to the age-related decline in muscle force and functional performance [13].…”