A Quick Guide to Levers

 A simple machine used to increase the efficiency of muscle contractions around a joint  Language of levers: ◦ Muscular effort: how hard a muscle has to work to pull a load ◦ Fulcrum – the support or point on which a lever moves  In the case of muscle movement, the joint is the fulcrum ◦ Resistance – the weight of the object you are trying to move ◦ Distance – the amount of space between the fulcrum and the load, and the fulcrum and the site of muscular effort ◦ Class – the type of lever; based upon the site of the fulcrum, the site of the muscular effort, and the site of the resistance

 The degree of muscular effort required to overcome resistance to movement at the joint depends upon: ◦ the force of the resistance (weight); ◦ the distance from the fulcrum to the site of muscular effort; ◦ and the distance from the fulcrum to the site of resistance  *WHAT THIS MEANS*  How hard your muscle has to work to cause movement at the joint depends upon: ◦ how heavy the object is that you want to move (the resistance); ◦ how far away the joint (fulcrum) is from the muscle being used to move the object; ◦ and how far away the joint is from the object that you are trying to move

 The human body moves all things through force  Bones act as the levers, while joints perform as living fulcrums  Skeletal muscles create motion by pulling on tough cords of connective tissue called tendons ◦ These tendons in turn pull on the bone which creates motion  Muscles move bones through mechanical leverage ◦ As a muscle contracts, it causes the bone to act like a lever with the joint serving as a fulcrum  Muscle exerts force by converting electrical energy (from the brain) and chemical energy (created during respiration and digestion) into tension and contraction ◦ When a muscle contracts, it shortens, pulling a bone like a lever across its hinge  Muscles move and this causes us to move  We are capable of performing a wide variety of movements, but, muscle itself moves only by becoming shorter  They shorten and then they rest - a muscle can pull but it cannot push

 Levers are classified by the following: ◦ The position of the joint (fulcrum) compared to:  The site of the muscle pull, and;  The site of the weight (resistance or load) you are trying to move

 The joint (fulcrum) lies between the pulling muscle and the weight (load)  Most efficient class of lever  Can provide strength or speed depending upon the location of the fulcrum  Example – The neck joint during neck extension ◦ Fulcrum = The joints between the cervical vertebrae ◦ Muscle = The muscles on the back of the neck ◦ Load = A weight hanging from the head F M L

FM L

 The weight (load) lies between the joint (fulcrum) and the pulling muscle  Gives the advantage of strength  Example – The metatarsal-phalangeal (toe) joint during plantar flexion ◦ Fulcrum = The toe joint ◦ Muscle = The muscles of the calf ◦ Load = The body weight L FM

F M L

 The pulling muscle lies between the joint (fulcrum) and the weight (load)  Least efficient class of lever – only advantage is speed of movement  Example – The elbow joint during flexion ◦ Fulcrum = The ulnar-humeral joint ◦ Muscle = Biceps brachii ◦ Load = Weight in the hand F M L

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