Biomechanics Lecture 12 (4) - PDF

 PULLEYS A Pulley is a grooved wheel which is rotated about a fixed axis by a rope which passes round it The axis is supported by a framework or block and the whole structure may be used either as a fixed pulley or a movable pulley  Pulleys are used in both streng...

 PULLEYS A Pulley is a grooved wheel which is rotated about a fixed axis by a rope which passes round it The axis is supported by a framework or block and the whole structure may be used either as a fixed pulley or a movable pulley  Pulleys are used in both strength exercises and traction of body segments to change the direction of a force; these pulleys are single fixed pulleys. A pulley can also be used to increase or decrease the magnitude of a force; these pulleys are moveable pulley system.  FIXED PULLEYS This is used to alter the direction of a force and enables traction or weight to be applied at any angle The pulley block is fixed to some suitable support and the rope which passes round the wheel is attached to the weight at one end and effort on the other.  MOVABLE PULLEYS This is used to gain the Mechanical advantage to lift the heavy weight The upper pulley is fixed to an overhead support to which the rope is attached The rope is then wound round the movable pulley, to which the weight is attached The effort being applied at the free end  Anatomical Pulleys: In the human body, in most cases the pulley is replaced by a bone, cartilage or ligament and the cord is replaced by a muscle tendon. The tendon is lubricated in a manner so that it may easily slide over the pulley. Anatomical Pulley Improves muscle action as the muscle tendon passing over an external support which acts as a pulley Classification of anatomical pulleys : There are four classes of pulleys, the first three of them are examples of fixed pulleys and the fourth one is an example of a movable one. Class I: An improved muscle action comes from the muscle tendon passing over an external support, the external support serving as pulley. Eg. The presence of the patella ( the pulley) improves the efficiency of the quadriceps muscle as the pulley will increase the angle of insertion of the patellar tendon into the tibial tuberosity Class II: The action of the muscle at the joint is altered because of the pulley. e.g. 1: The pulley is a bone : e.g. the lateral malleolus of the fibula acts as a pulley for the peroneus longus muscle. If it was not for the malleolus, this muscle instead of passing behind the lateral malleolus to be inserted in the base of the first metatarsal and to produce ankle plantar flexion and eversion, it would have produced ankle dorsiflexion and eversion because of its passage in front of the ankle joint. Class II → The pulley is a bone Class II: 2- The pulley is a cartilage : e.g. The trochlea of the eye allows the superior oblique muscle of the eye when it passes over it to rotate the eye obliquely. Without this pulley, the muscle would have little effect on the eye. Class II → The pulley is a cartilage : Class II → The pulley is a cartilage :  Class II: 3: The pulley is a ligament: e.g. Retinacular structures, called pulleys, maintain the flexor tendons of the hand in constant relationship to the joint axes and promote economy and efficiency in finger flexion. This system is composed of the transverse carpal ligament, the palmar aponeurosis pulley, and the digital flexor pulley system.  In our hand there are muscles, for both flexion and extension. Thinking about flexion alone, these pulleys are fibrous bands of thickened deep fascia (retinaculum) that help stabilise the tendon. You may think of it as using a rubber band to fasten two sticks together. These fibrous bands help our flexor tendon adhere to the contours of our fingers, so that the tendon bends just as we would like it to whether we’re holding onto a rock/ Class III: The joint serves as the pulley. The size of the epicondyles of the femur gives the gracilis tendon a favorable angle of insertion as the tendon insert on the tibia. Or the middle part of the deltoid as it passes over the shoulder joint. Class III→ The joint serves as the pulley Class IV: The muscle acts as a pulley the muscle is its own pulley e.g. as the biceps muscle increases in size, its angle of insertion will increase. The muscle underneath acts as pulley for another muscle, which passes over it e.g. brachialis muscle, will raise the biceps giving it a better angle of insertion. For this to be effective, the overriding ms. must not have the same insertion as the bulky ms. Class IV: