How the Anatomical Pulleys in the Musculoskeletal System Increase Mechanical Advantage - Coursework Example

How the Anatomical Pulleys in the Musculoskeletal System Increase Mechanical Advantage s (Date) Introduction The body is a machine with various moving parts. The arrangements of these body parts give three kinds machines in the production of movement: wheels and axles, pulleys, and levers. The pulley systems within the body make several tasks easier. The musculoskeletal system has many pulley systems. The muscles, bones, and connective tissue including tendons, bursa, and ligaments create movement and force exertion, offer a framework for the body, and dictate the level of flexibility (Schuenke, Schulte, and Schumacher, 2012, p.34). The systems are in a constant state of motion whether moving at a constant velocity devoid of acceleration or at rest with no motion. First, the human bones’ mobility is dependent on muscle contraction. Muscles are responsible for the movement in the human body. Muscles function to produce motion and force (Kahn and Line, 2008, p.54). Second, tendons are tough and flexible band of fibrous connective tissue which joins muscles to bones. They transfer forces and movements from the muscles. Next, ligaments are groups of dense, white, fibrous elastic tissue. A ligament connects bones to bones in order to form a joint. Majority of the ligaments limit dislocation. They stabilise and support the joints by holding the joints together (Pheasant and Haslegrave, 2011, p.65). Lastly, bursa is fluid-filled sac located at bone joints and it is lined with a synovial membrane. It minimises friction by easing movement as muscles or tendons pass over the skin or bone. Therefore, drawing on a variety of sources the paper will discuss the biomechanical basis of anatomical pulleys in the musculoskeletal system with specific focus on how the pulleys can increase mechanical advantage using two examples from the body: patella and biceps brachii muscle. Discussion A pulley is a simple mechanical device that comprises of a wheel, which turns readily on an axle. The wheel is often grooved for wire or rope (Woodford, 2014, p.32). The pulley system is constructed either as a linear or concurrent force system. In this perspective, there are three types of pulleys: single fixed pulley, single movable pulley, and a pulley combination (Seller, 1993, p.45). First, the single fixed pulley changes direction of the force acting on it and also its magnitude remains the same on either sides of the pulley rope regardless to the angle of pull of force. As a result, it acts as a first class lever. The single movable pulley also acts as a second class lever. The pulley combination comprises of numerous combinations of the fixed and movable pulley. They act as third class levers. Since as cited by Stone, Stone, and Sands (2007, p. 54), the mechanical advantage is measure of performance of the machine by measuring the force of amplification attained using a machine system. In the human body, the pulley system is replaced by ligaments, bones, and muscle tendons (Dumbleton and Black, 1981. 387). There are four types of the anatomical pulleys. In Class I, these are fixed pulleys where an improved action of the muscle originates from the muscle tendon passing over an external support. The external support acts as a pulley. For example, the presence of the patella enhances the efficiency of the quadriceps muscle since the pulley will widen the insertion angle of the patella ligament into the tibial tiberosity. Class II is also a single fixed pulley where the action of the muscle at the joint is changed due to the pulley. For example, the lateral malleolus of the fibula acts as a pulley for the perobneus lungus muscle. If it was not for the malleolus, the longus muscle would have otherwise passed behind the lateral melleolus inserted in the base of the first metatarsal resulting in ankle plantar flexion as well as eversion. Besides, it would also have led to ankle dorsiflexion and eversion as a result of its passage in front of the ankle joint. Class III is also a single fixed pulley where the joint acts as the pulley. The size of the femur’s epicondyles provides the gracilis tendon with a suitable insertion angle as the tendon insert on the tibia. Class IV is a movable pulley. The muscles act as a pulley while the muscle is its own pulley. For instance, as the biceps muscles increases in size, the angle of insertion also increases in size. Besides that, the underneath muscles also act as a pulley for another muscle that passes over it. This raises the biceps providing it with a better angle of insertation. These pulley systems act in any direction to change the angle of action on the body providing, stabilization, resistance, and aid in movement (Kreighbaum and Katherine, 1996, p. 45-79). In the human body, the tendon of the skeletal muscle usually slides over a round a bony surface. The system acts as simple pulley. According to Vos (2013, p. 74), a simple pulley results in a change in the direction of the force or the pull of the muscle. However, there is no change in the amount force generated by the muscle. The tendons are lubricated in a way that it can easily slide over the pulley. Patella Focusing on the patella, it increases mechanical leverage of the quadriceps. The patellar is a single fixed pulley and the mechanical advantage is increased by changing the direction of the force. Figure 1: Single fixed pulley (The Engibeering Tool Box, 2015) In this case, the patella pulley system changes the course of a tendon or increasing the forearm distance from the joint in order to increase the muscle’s MA (Houglum and Bertoti, 2011, p. 72). The knee acts as a simple pulley where the quadriceps femur extends the leg. Studies have evidenced that when pulleys are fixed, they provide mechanical advantage by changing the direction of the force (Uicker, Pennock, and Shigley, 2010, p.87). In the bio-mechanical advantage, the origin and insertion of the muscle dictate the mechanical advantage. If the insertion is near the axis or joint, this requires more powerfull movement resulting in movement in an increased distance. As noted by Levangie and Norkin (2011, p. 420), the patella is a single fixed pulley because it is fixed firmly inside the femur’s intercondylar notch. In a view shared by Houglum and Bertoti (2011, p. 72), even though the angles of muscle pull may vary due to the pulley mechanism; the force vector of the muscle remains straight. The line of action of the muscle is from the immediate attachment point of the muscle to the bone extending into space based on the magnitude of the force. Correspondingly, the patella’s position changes the quadriceps’ pull position on the tibial tuberosity resulting in an increase of the mechanical advantage. Figure 2: Biomechanical pulley of the patella (Schafer, 2014). In the patella, the muscle-bone connections operate on the principle of a pulley that alters direction when a force is applied. It changes the direction in which the duadriceps tendon pulls the tibia (Kreighbaum and Barthels, 1996). The belly of the quadriceps muscle is parallel to the femur. The tendon muscle passes over the knee’s joint and attaches to the tibia through the patella tendon at the tibial tubercle. As for the knee extension, the axis of the joint is regarded to be situated through the femoral condyles. The mechanical advantage of the quadriceps muscle force (QLf) lies in the space between the joint axis and vector. As shown in Figure (3A), without the patella, the quadriceps muscle line of pull on the segment of leg and foot would follow the patellar tendon at the tibilial tubercle lying parallel to the leg-foot segment. On the contrary, Riihimaki (2013) asserts that the patella is situated between the femur and quadriceps tendon. Therefore, altering the angle which the patellar tendon makes with the leg or tibia as well as varying the quadriceps muscle line of pull of away from the knee joint axis as seen in Figure (3B) below the influence of changing the line of pull of the quadriceps muscle on the tibia (QLf) increases the mechanical advantage. Figure 3: The patellar (Morris, 1999) The quadriceps muscles maintain a reasonable ability to provide torque in full knee extension. However, the patella makes a minimal contribution to its moment arm (Levangie and Norkin, 2011, p. 420). Biceps brachii muscle The second anatomical pulley in the musculoskeletal system is the biceps brachii muscle. It is a type of a single movable pulley. In the single movable pulley, the effort is half or more as a result of load efficiency (The Engibeering Tool Box, 2015). The pulley system provides mechanical advantage requiring only half the effort required to lift the weight of the load (Loudon, Manske, and Reiman, 2013, p.20) Figure 4: Single movable pulley (The Engibeering Tool Box, 2015). The biceps branchii are two-headed muscle located in the upper arm between the elbow and shoulder. Both heads originate from the scapula and proceed to join forming a single muscle belly that is attached to the upper forearm. Whereas the biceps crosses both the elbow together with the shoulder joints, its main function is to flex the forearm and supinate the forearm (Lippert, 2006, p.126-7). Both these movements simulate the movable pulley system as shown in figure (5) below. Figure 5: biceps brachii muscle (Karistinos and Paulos, 2007, p.3). Dirim et al. (2008, 248) argue that the biceps brachii muscle is made up of long and short head muscle bundles. The long head is the larger of the two muscle bodies which form the biceps branchii muscle. Figure 6: Short and long head biceps branchii muscle bundles (Dirim et al., 2008, 248). The long head originates just above the shoulder joint (at the supraglenoid tubercle of the scapula), and inserts on the radius bone of the forearm. It makes a sharp turn at the humeral head and continues its course in the bicipital grove. The tendons are lubricated in such a way that it they can easily slide over the bone in the pulley system (McFarland, 2011, p. 213). On the other hand, the short head originates from the top of the scapula (coracoids process). It also inserts on the tuberosity of the radius. When both heads join on the middle of the humerus, they form a common muscle belly. The biceps branchii ends in two tendons. When the humerus is in motion, the long head’s tendon is held firmly in place in the intertubecular groove by both the lesser tubercles and greater tubercles in addition to the overlying transverse humeral ligament. During the external to internal motion, the tendon is forced against the lesser tubercle in the middle. This ensures the tendons remain in their groove during movement (Simons, Travell, and Simons, 1999, p.648-49). As a result, there is a forearm flexion, forearm supination (turning of the palm hand up), and upper arm flexion (raising the arm upwards and forward). Figure 7: Biceps branchii pulley system (Karistinos and Paulos, 2007, p.2). The biceps is tri-articulate because it operates across three joints, including the proximal radioulnar joint (upper forearm), humeroulnar joint (elbow), and glenohumeral joint (shoulder). All these joint work together as movable pulley systems. These three joints work together to reduce the muscle force required to perform a task. The muscle-tendon unit of long head of biceps muscle acts as a complex pulley system. When the elbow flexes, it abducts the shoulder and also result in the supination of the radioulnar joint in the forearm. This movement reduces the effort used to perform a task. In the same way, there is a muscle length that generates optimal strength. Kang, Seo, Park, Dong, Seo, and Han (2013, pp. 1134-36) note that when muscle length reduces, the muscle activation increases. When the biceps brachii muscles increases in size, the angle of insertion increases in size, as well. Besides that, the underneath muscles also act as a pulley for another muscle that passes over it. This raises the biceps providing it with a better angle of insertion, thus increasing the mechanical advantage. The task of movement is made easier by the biceps brachii muscle deflecting the action line of the muscle away from the joint axis, thus increasing the MA of the muscle force. By increasing the mechanical advantage, the incidences of shoulder pain are reduced. This is because a study by Braun et al. (2011, p.790-795) found out that an increase in MA allows the biceps tendon to shift off the groove resulting in anterior shoulder pain. Giacomo, Pouliart, Costantini, and Vita (2009, p. 102) argue that the biceps pulley system protects the long head biceps tendon from the shearing stress. Besides that, Doral (2012, p. 77) adds that it also prevents the external rotation of the adducted shoulder. Conclusion In summary, the musculoskeletal system consists of muscles, bones, and connective tissue, including the ligaments and tendons. The arrangement of these components provides three types of movement in the production of movement, including wheels and axles, pulleys, and levers. In the human body, the pulley systems have the function of redirecting a force to make a task easier. In the musculoskeletal system, the task is actually movement so as to rotate the body segment. The biceps anatomic pulley makes the task easier by deflecting the action line of the muscle away from the joint axis. The three joints reduce the effort required to perform a task. As a result, the mechanical advantage of the muscle force is increased. As for the patella anatomical pulley system, the changes of course of a tendon or increasing the forearm distance from the joint increases the muscle’s mechanical advantage. By increasing the mechanical advantage for a muscle force, a force of similar magnitude results in the production of greater torque. References Braun, Sepp, et al. 2011. “Lesions of the Biceps Pulley,” The American Journal of Sports Medicine, 39(4): 790-795. 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