E2 Transmission Tendons

Topic

This tendon transmits the muscle's force—specifically the force of the muscle that defines this particular biomechanical model—to the organism's skeleton. However, the tendon does not behave like a rigid cable; instead, it exhibits non-linear viscoelastic behavior: an initial region of low stiffness—where the tendon's wavy collagen fibers are still being straightened and tensioned—precedes a linear region of much higher stiffness, which ultimately culminates in tendon rupture if the applied load continues to increase.

The tendon's final stiffness is a key factor in sports biomechanics—a property that is altered in conditions like chronic tendinosis. A stiffer tendon transmits muscle force to the joint more rapidly but stores less elastic energy, whereas a more elastic tendon acts like a spring, returning stored elastic energy with each movement; this is the function performed by the heel tendon, which stores a significant amount of elastic energy during a runner's stride. Increased tendon stiffness results in a higher transmission velocity of muscle force to the joint, albeit at the expense of the elastic energy the tendon can store.

The collagen within the tendon possesses a remarkably high modulus of elasticity—a property that is reduced in cases of chronic tendinosis.

The tension borne by the heel tendon can exceed the organism's total body weight several times over during a jump—an extraordinary mechanical demand placed upon the tendon described in this model. Consequently, this model—characterized by the non-linear viscoelastic behavior introduced at the outset—allows both the Kelvin-Voigt rheological model (featuring a spring and damper in parallel) and the Maxwell rheological model (with the same components in series) to describe the tendon's final viscoelastic behavior. The tendon's hysteresis during a loading-unloading cycle indicates a moderate energy loss—even in a healthy tendon—which is significantly lower than the heightened hysteresis observed in a chronically degenerated tendon. Chronic degeneration causes this hysteresis to increase well beyond the moderate energy loss seen in the healthy tendon used to establish the initial model.

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