AN INVESTIGATION OF THE RELATIONSHIP BETWEEN MUSCLE AND TENDON ARCHITECTURE AND THEIR MECHANICAL PROPERTIES

Objective: This study aimed to investigate the effects of the architectural features of the gastrocnemius muscle-namely fascicle length, pennation angle, and muscle thickness-and Achilles tendon thickness on the mechanical properties (elasticity, stiffness, and tone) of both the gastrocnemius muscle and the Achilles tendon. Method: Sixty-three healthy female volunteers aged 18-27 years without musculoskeletal symptoms participated in the study. The pennation angle, thickness, and fascicle length of the gastrocnemius muscle and the thickness of the Achilles tendon were measured using an ultrasonography device with a linear probe (5-12 MHz) (MicrUs EXT-1H, Telemed Ultrasound Medical Systems, Vilnius, Lithuania). A portable myotonometer (MyotonPRO, Myoton Ltd., Tallinn, Estonia) was used to assess the mechanical properties of the medial gastrocnemius and Achilles tendon, including logarithmic decrement (elasticity), dynamic stiffness (stiffness), and oscillation frequency (tone). Results: Data analysis revealed no significant relationships between fascicle length, pennation angle, or muscle thickness of the gastrocnemius and its mechanical properties (p>.05). Similarly, no significant associations were not found between Achilles tendon thickness and its mechanical characteristics (p>.05). However, the dynamic stiffness of the Achilles tendon showed a moderate positive correlation with body mass index (r=.364, p =.003), gastrocnemius thickness (r=.278, p=.032), pennation angle (r=.285, p=.023), and subcutaneous fat thickness (r=.328, p=.009). Conclusion: This study demonstrated that muscle and tendon architecture does not directly determine their mechanical properties. However, higher body mass index, increased muscle thickness, and greater pennation angle may elevate the mechanical load on the tendon, potentially increasing Achilles tendon stiffness. These findings highlight the importance of considering anthropometric characteristics in addition to structural parameters when evaluating tendon and muscle mechanical properties.