Longitudinal and transverse deformation of human Achilles tendon induced by isometric plantar flexion at different intensities

Abstract

The present study determined in vivo deformation of the entire Achilles tendon in the longitudinal and transverse directions during isometric plantar flexions. Twelve young women and men performed isometric plantar flexions at 0% (rest), 30%, and 60% of the maximal voluntary contraction (MVC) while a series of oblique longitudinal and cross-sectional magnetic resonance (MR) images of the Achilles tendon were taken. At the distal end of the soleus muscle belly, the Achilles tendon was divided into the aponeurotic (ATapo) and the tendinous (ATten) components. The length of each component was measured in the MR images. The widths of the Achilles tendon were determined at 10 regions along ATapo and at four regions along ATten. Longitudinal and transverse strains were calculated as changes in relative length and width compared with those at rest. The ATapo deformed in both longitudinal and transverse directions at 30%MVC and 60%MVC. There was no difference between the strains of the ATapo at 30%MVC and 60%MVC either in the longitudinal (1.1 and 1.6%) or transverse (5.0∼11.4 and 5.0∼13.9%) direction. The ATten was elongated longitudinally (3.3%) to a greater amount than ATapo, while narrowing transversely in the most distal region (-4.6%). The current results show that the magnitude and the direction of contraction-induced deformation of Achilles tendon are different for the proximal and distal components. This may be related to the different functions of Achilles tendon, i.e., force transmission or elastic energy storage during muscle contractions.

Is human Achilles tendon deformation greater in regions where cross-sectional area is smaller?

“…Similar elongations between these two components of the Achilles tendon with markedly lower forces acting on the gastrocnemius tendon component are in line with our assertions of a lower stiffness for the proximal (gastrocnemius) compared with the distal Achilles tendon. Because of the greater length of the proximal Achilles tendon (gastrocnemius) compared with the distal region, these elongations correspond to smaller longitudinal strains in the proximal tendon component, consistent with MRI-based findings at 30% and 60% of MVC (Iwanuma et al, 2011). These previous reports, however, reflect overall 'end-to-end' length changes of these tendon components rather than more detailed region specificity as examined in the present study.…”

“…An increased width measured at the gastrocnemius MTJ was noted upon contraction in a previous report (Farris et al, 2013). In another report, an increased width of the proximal (gastrocnemius) Achilles tendon component but a decreased width of the distal Achilles tendon component during contractions at 30% and 60% of MVC was noted (Iwanuma et al, 2011). Whilst girth measurements at a single site such as the MTJ may result from muscle bulging, tensile deformation of a tendon should only result in thinning of its overall CSA (Poisson's ratio) and therefore consideration of only one axis in the transverse plane may not reveal the true nature of deformation during tendon loading.…”

Negative Poisson’s ratios in tendons: An unexpected mechanical response

“…A few studies have also investigated the Poisson's ratio of tendons, both experimentally [2,[14][15][16][17][18][19] and numerically [20,21]. The Poisson's ratio [22] is a fundamental material property in its own accord and describes the change in size of a system in a direction perpendicular to an applied stress.…”

Imaging Studies of the Mechanical and Architectural Characteristics of the Human Achilles Tendon in Normal, Unloaded and Rehabilitating Conditions

“…Reconstruction of the lower limb muscle connective tissue from axial anatomical MR images (Iwanuma et al 2011;Kinugasa et al 2010) and from the Visible Human data ) reveals a complex and somewhat consistent internal structure. The Achilles tendon is rather flat near its broad insertion to the calcaneus but becomes oval in the mid-region and then sheet-like as it courses proximally over the posterior surface of the soleus muscle ( Figure 3, Hodgson et al 2006;Kinugasa et al 2010).…”

“…The Achilles tendon is rather flat near its broad insertion to the calcaneus but becomes oval in the mid-region and then sheet-like as it courses proximally over the posterior surface of the soleus muscle ( Figure 3, Hodgson et al 2006;Kinugasa et al 2010). The overall length of human tendon is approximately 68 mm and its width becomes larger as the region shifts more distally from the insertion of the soleus muscle (approximately 13 mm) to the calcaneus (approximately 28 mm) (Iwanuma et al 2011). A small portion of the tendon and aponeurosis forms a ridge that protruds into the distal portion of the soleus and often reached the anterior surface of the soleus muscle.…”