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Thesis Format

Integrated Article

Degree

Master of Science

Program

Kinesiology

Supervisor

Rice, Charles L.

Abstract

The ability to rapidly generate muscular torque and velocity is important in specialized activities and daily tasks of living. Tendon stiffness is one factor in the neuromuscular system that influences musculoskeletal torque transmission. Previous studies have reported weak-to-moderate correlations between tendon stiffness and rate of torque development (RTD). However, these correlations have been reported only for isometric contractions which may not be relevant to contractions involving joint rotation (i.e., dynamic). The purpose was to investigate the effect of calcaneal tendon stiffness on the dynamic rates of torque (RTD) and velocity (RVD) development in plantar flexor muscles. Young adult males (n=13) and females (n=2) performed prone isometric- and isotonic-mode plantar flexion maximal voluntary contractions (MVC). Ultrasound imaging was used to quantify tendon morphological characteristics to estimate Young's elastic modulus (YM). Maximal voluntary and electrically evoked (300 Hz) isometric- and isotonic-mode (at 10% and 40% MVC loads) contractions were evaluated for RTD and RVD through a 25° ankle joint range of motion. YM was correlated modestly with isometric RTD, but only for evoked contractions (RTD0–50 ms: r=0.54, p=0.02, RTD0–200ms: r=0.62, p=0.01). Conversely, YM was not correlated with dynamic RTD (voluntary: r=-0.07–0.41, p=0.06–0.40, evoked: r=-0.2–0.3, p=0.14–0.24) nor RVD (voluntary: r=-0.08–0.24, p=0.27–0.40, evoked: r=0.12– 0.3, p=0.14–0.34). These correlations would indicate that calcaneal tendon stiffness is an important factor for rapid isometric torque development, but a smaller factor for isotonic contractions. The determinants of dynamic contractile rates likely involve more factors than isometric contractions and warrant further study.

Summary for Lay Audience

Muscular torque and velocity are two parameters involved in human purposeful movements. The rates of torque and velocity development are important for specialized and daily tasks (e.g., explosive athletic performance and correcting perturbations in balance, respectively). Several factors of the neuromuscular system influence these rates, one of them being the stiffness of the tendon. Stiffer tendons may provide a mechanical advantage as force transmission from the muscle to the bone is optimized. Previous research has shown positive correlations between tendon stiffness and explosive torque development however, the contractions for rate of torque development determination have only been explored in isometric contractions in which there is no joint rotation. Much less is known about these factors in contractions that involve appreciable muscle shortening (i.e., dynamic contractions) during joint movement. Ultrasound imaging was used to gain a measure of tendon elongation so stiffness could be determined during dynamic contractions. These values were plotted against a participant’s maximal rate of torque and velocity development at different loads to initiate movement of the dynamometer. We found no significant correlations between tendon stiffness and dynamic rates of torque and velocity development. This indicates that determinants of dynamic contractile rates may differ from isometric contractile rates. Future studies are required to explore additional determinants involved in dynamic contractions that may differ from isometric contractions. Considering torque and velocity are critical for optimal power generation, the opportunity for translational research in this field to improve and understand functional outcomes will be important for continuing studies.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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