Morphological and mechanical properties of the human triceps surae aponeuroses taken from elderly cadavers: Implications for muscle-tendon interactions

Abstract

The human triceps surae (two gastrocnemii and soleus) has aponeuroses in the proximal and distal aspects, the latter of which insert into the calcaneus by sharing the common Achilles tendon. These tendinous tissues are known to have elasticity and upon muscle contraction the aponeurosis is stretched both longitudinally (along the muscle’s line of action) and transversely. Higher aponeurosis transverse deformability has been documented, but there is a paucity of information on the morphology and mechanical properties of human aponeurosis. This study aimed to identify morphological and mechanical characteristics of the human triceps surae aponeuroses. Twenty-five triceps surae muscle-tendon units were procured from 13 human donors (formalin fixed, 6 males, 7 females) aged 67–91 years. Specimens of aponeuroses were excised from the eight regions (posterior and anterior regions of the gastrocnemius medialis and lateralis, medial and lateral parts of soleus; proximal, middle, and distal sites each, 2–4 cm × 2–4 cm). Aponeurosis thickness was measured using a digital caliper. Uniaxial tensile tests were implemented to determine the mechanical properties of specimens loaded longitudinally (along the muscle’s line of action) and transversely. The aponeurosis thickness showed significant differences between muscles and sites, while Young’s modulus showed direction-dependent (longitudinal vs. transverse) differences within sites. Results show different morphology and mechanical properties of aponeuroses between synergist muscles. The reason for site-dependent differences in stiffness is due to a reduced aponeurosis thickness rather than a reduction in the material property. The anisotropic elastic feature (differences between longitudinal and transverse directions) of the aponeuroses was more pronounced than previous in vivo findings, suggesting inherent material design of the aponeurosis that matches three-dimensional contractile behavior of muscle fibers.

Objective Assessment of Regional Stiffness in Achilles Tendon in Different Ankle Joint Positions Using the MyotonPRO

“…This result is consistent with a previous study which found that the Achilles tendon became stiffer after stretching [ 27 ]. Shan et al (2019) demonstrated that the stiffness of the medial head of the gastrocnemius and medial and lateral soleus was correlated with ankle joint position or muscle contraction [ 29 ]. Further, there was a significant increase in shear modulus of the medial head of the gastrocnemius and the lateral head of the gastrocnemius in the lengthened muscle position [ 26 , 30 ].…”

“…These cases demonstrate the straining-stiffness behavior of muscles and tendons after the fibers become tight [ 31 ]. Many studies identified the stiffness of muscle in a tension state, but only a few studies focused on the change of tendon stiffness after stretching [ 29 , 30 ]. When the tendons and muscles respond to the same mechanical load, such as tension, they may have different stiffness modulation [ 32 ].…”

Anisotropic and viscoelastic tensile mechanical properties of aponeurosis: Experimentation, modeling, and tissue microstructure

“…There is clear importance of the aponeurosis in musculoskeletal function, but there have been relatively few studies of aponeurosis material properties to date Bojsen-Møller and Magnusson, 2019;Shan et al, 2019). Determining the material properties of the aponeurosis will provide evidence of its structure and function to identify how it contributes to the movement of the musculoskeletal system.…”

A Simulation-Based Analysis of The Effects of Variable Prosthesis Stiffness On Interface Dynamics Between The Prosthetic Socket and Residual Limb

“…Due to a lack of information reported in previous literature, damping coefficients (N×s/mm) were set to half the numerical value of stiffness (N/mm) in an effort to reduce high frequency oscillations at the contact interfaces, which can lead to rapidly-evolving ordinary differential equations and thus computational instability when simulating interface dynamics. (Zheng et al, 1999) 2 (Mak et al, 1994) 3 (Shan et al, 2019) The static coefficient of friction (µstatic) between the limb and socket was assigned a value of 0.5, based on an in vivo study of the interaction between silicon (a commonly used material for prosthetic socket liners) and the skin of the human leg (Zhang and Mak, 1999). Coefficients of friction between 0.5 and 3.0 have been reported for various other socket liner materials (Cagle, Hafner, Taflin, & Sanders, 2018; Joan E Sanders, Greve, Mitchell, & Zachariah, 1998).…”