Tendon Elasticity

Question: Describe the structure and function of tendons, mechanical properties of tendons, changes in Kinetic and Potential Energy and tendon support in locomotion? Answer: Structure and function of tendons Tendons have properties of elasticity which help them to be flexible and angulated around the bones or joints. They receive their blood supply from the covering of the tendons (vessels in perimycium), periosteal insertions and also from the surrounding tissues. The attachment by the tendons is very important and it is present where the point of insertion is at a distance or where the muscle exertion power is more across a joint. When the tendons stretch themselves and recoil, the metabolic energy gets saved and is thereafter used in locomotion. It stores and returns the elastic strain energy when the kinetic energy is lost during locomotion. (Antony, 2016) Tendons enable the mammals and birds to run and jump. They play an important role in position control while stopping by controlling the force exerted to initiate a jump. This is done by recoiling which is much faster than the action of muscles to shorten themselves. Tendons in a body perform functions to connect muscles to bone, to provide muscles a pinnate arrangement to perform various tasks. They help in contraction and relaxation of the muscles by sometimes extending up as intramuscular tendons. Their main function is to transmit tensile forces generated by the muscle cells and bring about compression and shear as they work around bony or fibrous structures. (Passerieux, 2007) Mechanical properties of tendons Although the function of tendons is tightly integrated, but their mechanical role of contraction during locomotion is independently performed. Alone the muscle fibers cannot work with perfect mechanical force, but when accompanied with tendons makes a muscle-tendon unit which enhances the performance for a wide variety of locomotors activities. When an activity of lower mechanical energy is needed like steady-speed running, then tendons save the mechanical energy by reducing muscle work and recovering cyclic changes in the muscles. The reduced muscle work develops high forces in the skeletal muscle fibers and allows muscle fibers to work isometrically. This action is carried out by stretching and recoiling of the associated tendon. Evidences have suggested that while running, the acceleration gets transferred directly from the muscle to the tendon resulting in its stretch. The stored energy in the tendon gets released and thus the energy level in the body also rises up to perform the task. This periodic change in the length of tendons helps to distribute the muscle power equally and provides independent flexion/extension movement to occur at a joint. (Robert, 2002) Changes in Kinetic and Potential Energy The utilization of the elastic energy and its reuse during locomotion/running is a result of change that occurs in the kinetic energy of the runner. The center of mass of the limb absorbs the kinetic and potential energy thus slowing down first half of the step. The stored energy only helps in performing half of the activity and the other half is done by the cyclic work of the contractile elements. The energy saved by the elastic mechanism of the runners is not only to reduce muscle work but to allow the muscles to operate at shortened velocities which are necessary for the production of force during running. Apart from the fluctuations in the mechanical energy, the running animals move at a steady speed to generate sufficient muscle force so that their body weight remains supported. The evidences from the studies of muscle and limb dynamics have suggested that tendons stretch early in the step of muscle shortening which is the energy directly transferred from the muscle during the running accelerations. The stored energy in the tendons is then released to empower the increase in energy of the body. This change in length of the tendon redistributes the muscle power and enables the contractile elements to shorten at constant velocities. (Thomas, 2002) Tendon support in locomotion The stiffness of the collagens makes it ideal to function properly as a spring in the tendons of vertebrates; 91-95 percent of the energy stored by the tendons on stretching can be removed by the elastic recoiling of the tendon fibers. The tendon requires much less maintenance and operating cost per unit mass than that compared to a muscle (300-500 fold).this relationship reaches to its maximum when the required force is transmitted completely by the passive stretch of the tendon. Animals energy is worked out directly by the muscle to operate, maintain and move relatively with the tissue mass, otherwise it would be carried out by the tendons passively. To better understand the function and use of tendons in the locomotors activities of animals, an example of ostrich and Maos can be taken. Ostriches are said to be the fastest running bird on the planet. The reason behind it is the structure of legs designed in such a way so as to control and maximize its speed and duration during a run. When measurements were taken to find the reason behind, it was found that maximum stress is laid on the muscles and tendons of legs and highest amount of forces takes place during the initiation and termination of the run. Like ostriches maos are also flightless birds that have heavier and thicker bones than ostriches. Their body mass is greater than the weight in their bones which allows them to run fast and lay less stress on tendons. Conclusion The tendon elasticity and muscle work that helps animals in locomotion and the mechanics behind it lies under the architecture system of the muscle-tendon unit. Muscles generally contribute only to the mechanical work whereas tendons play a major role in providing elastic energy to the animal to perform a specific task. They provide majority of muscle activity by saving the elastic energy and using it when required. The various forces acting on the body (eccentric or isometric) are enhanced which reduces the energy expenditure and provides balance and comfort during an activity. References Benjamin, M., Kaiser, E. and Milz, S. (2008). Structure-function relationships in tendons: a review.J Anatomy, 212(3), pp.211-228. Bennett, M. (2009). 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