Understanding Achilles Tendinopathy and Tendon Rehabilitation through the Achilles Tendon Diametral Strain Response to Eccentric Exercise

We have previously demonstrated that eccentric exercise results in an immediate decrease in tendon thickness in healthy young adults [3]. Based on in vitro evidence, it was proposed that the marked diametral strain response (≈ 20%) observed in vivo primarily reflected the radial extrusion of fluid from the tendon [4, 5]. Such convective fluid movement likely plays a vital role in tendon homeostasis by enhancing molecular perfusion [6] and may represent a biologically plausible mechanism by which eccentric exercise promotes tendon healing. To date, however, the diametral strain response of tendon to eccentric exercise has only been examined in participants without tendinopathy. It is imperative to determine the diametral strain response in tendinopathy as the condition is associated with structural changes including collagen fibril disorganisation and thinning as well as an increase in the concentration of hydrophilic glycosaminoglycans (GAGs) [2, 7]. These structural changes may impact upon the proportion of free water within the tendon and the way in which collagen extends and realigns with loading. As such, convective fluid movement may be reduced in the presence of tendinopathy.