2 Movement analysis When you have worked through this chapter, you will have developed a knowledge and understanding of: ● rst, second and third class levers and their use in physical activity ● mechanical advantage and disadvantage of the body’s lever systems and the impact this has on sporting performance ● planes and axes of movement applied to sporting actions. 837021_ch02.indd 47 02/02/16 5:04 PM 2.1 Levers Levers are seen in everyday life as well as in sport and exercise. A lever system is a rigid bar that moves around a fi xed fulcrum with two forces applied to it. Key terms Levers can change the size or direction of the eff ort used to make a task more Lever: A rigid bar or object that manageable. moves around a xed fulcrum All levers consist of three key elements: with two forces applied to it. Fulcrum: A xed pivot point. For 1 Fulcrum: a fi xed pivot point. example, a joint in the body. 2 Eff ort: the source of the energy that will do the work. 3 Load: the weight/resistance to be moved. Eff ort: The source of the energy. For example, muscles in the body. Activity Load: The weight/resistance to be moved. For example, a body part 1 plus anything held or resistance met. Key term Class of lever: The type of lever. There are rst class, second class and third class levers. The picture shows how a lever can be useful. a) Explain how this lever works and what advantage a person gains using Exam tip a lever in this situation. b) Can you identify the fulcrum, e ort and load in the picture? You will be expected to draw and label simple lever set-ups, so you’ll First, second and third class levers need a method for remembering the di erence between rst, There are three classes of lever: fi rst class levers, second class levers and third second and third class levers. class levers. The positioning of the fulcrum, load and eff ort in relation to each other will determine what class the lever is. Try imagining: one see-saw, two wheelbarrows and three In the human body, the musculo-skeletal system creates levers around every shing rods. joint. These allow us to move. The joint acts as the fulcrum, eff ort comes from contracting muscles and the load is the body part being moved, plus any Or use the mnemonic “1, 2, 3, F, additional objects held or resistance met. The body contains all classes of lever, L, E” to help you remember the but third class levers are most common. middle element of each class of lever. 48 837021_ch02.indd 48 02/02/16 5:04 PM Class of Lever drawing Well-known example for Best example in the lever you to remember easily human body First class lever Load Effort Load Effort Fulcrum Fulcrum Second Effort class lever Load Effort Load Fulcrum Fulcrum Third class lever Load Effort Effort Fulcrum Load Fulcrum Exam tip Activities It is important to think about where a muscle attaches to the 2 Using a ruler, a rubber and a pencil, make bone when labelling the e ort. This is especially key at the elbow. a rst class, second class and third class The biceps attach between the fulcrum (the elbow joint) and the lever. You will need to act as the e ort. load, meaning a biceps curl uses a third class lever. The triceps 3 Experiment with the examples of levers in attach behind the fulcrum, meaning that a triceps extension uses the human body given, to increase your a rst class lever. understanding. Nod your head backwards and forwards imagining the pivot point in Shoulder the middle ( rst class lever); move up and down on your tip toes pivoting on the Biceps Triceps ball of your foot (second class lever); and perform the upward phase of a biceps curl, recognising that your biceps Wrist Elbow muscle is pulling on your forearm (third class lever). 49 837021_ch02.indd 49 02/02/16 5:06 PM 2.2 The bene ts of different levers There are two main benefi ts of lever systems: Key terms 1 Large loads can be moved with a relatively small amount of eff ort. 2 The distance a load can be moved, or the speed with which it can be Load arm: The distance from the moved, can be increased without an increase in eff ort. load to the fulcrum. Eff ort arm: The distance from the To work out the benefi t of a particular lever, you need to look at the length of e ort to the fulcrum. two arms. The distance from the load to the fulcrum is known as the load arm, while the distance from the eff ort to the fulcrum is known as the eff ort arm. Activity 4 Draw a simple diagram of each of the three lever classes and label the e ort arm and load arm. Here is an example of a rst class lever to show you how this is done. Load Effort Load arm Effort arm Fulcrum Mechanical advantage and disadvantage Mechanical advantage When a lever’s eff ort arm is longer than its load arm it is said to have mechanical advantage. Levers with mechanical advantage can move large loads with a relatively small amount of eff ort. They have a high load force to Key term eff ort ratio. Second class levers always have mechanical advantage. Mechanical advantage: Second If we consider a long jumper taking off , we see how the second class lever, class levers allow a large load to where the foot contacts the ground, has a high mechanical advantage because be moved with a relatively small the eff ort arm is longer than the load arm. The result of this, for the long amount of muscular e ort. jumper, is that the force produced by the muscles, which is relatively small, is able to drive the full weight of the athlete off the ground. Load Effort Effort Load Fulcrum Fulcrum 50 837021_ch02.indd 50 02/02/16 5:07 PM Mechanical disadvantage Key term When a lever’s load arm is longer than its eff ort arm, it is said to be at a mechanical disadvantage. It has a low load force to eff ort ratio. Third class Mechanical disadvantage: Third levers always have mechanical disadvantage. class levers cannot lift such heavy loads, with the same amount of Despite operating at mechanical disadvantage, third class levers are able to e ort, as second class levers due increase the distance covered and, therefore, the speed at the end of a lever to the position of the fulcrum in arm. They can produce a larger range of movement with relatively low eff ort. relation to the e ort and load. The hip joint is a third class lever. It cannot produce the same load force to eff ort ratio as a second class lever. However, this doesn’t mean that it is not good at what it does. Third class levers can take a small movement near the fulcrum and make a large movement where the load is. This provides a relatively large range of movement, which results in relatively high speed being produced. Effort Effort Load Load Fulcrum Fulcrum First class levers: mechanical advantage and disadvantage In the case of fi rst class levers, the position of the fulcrum is key. If the fulcrum is closer to the load, then relatively low eff ort will result in larger, more powerful movements at the load end; there will be mechanical advantage. If the fulcrum is closer to the eff ort, then the lever will operate at mechanical disadvantage but will produce a larger range of movement at the end of the lever and greater speed as a result. Activity 5 a) Look at these rowers and discuss the class of lever that the oars create. b) What is the bene t of this lever system to the rowers’ performance? 51 837021_ch02.indd 51 02/02/16 5:08 PM Planes and axes of movement 2.3 applied to sporting actions Planes and axes can be used when describing movement patterns. A plane is an imaginary line or surface that divides the body into two. Movement occurs Key terms in a plane. An axis is an imaginary line around or about which the whole body Plane: An imaginary line dividing or part of the body can turn. the body into two. Planes and axes are both drawn through a body standing in the anatomical Axis: An imaginary line around position (upright, with arms by the side of the body and palms facing which a body or body part can forwards). All movements are then described from this starting point. turn. “Axes” is the plural of axis. Frontal plane The frontal plane divides the body vertically from front to back. Movement occurs in the frontal plane about the sagittal axis. The sagittal axis passes horizontally through the body from front to back, allowing abduction and adduction. Sagittal axis The transverse plane divides the body horizontally from front to back. Movement occurs in the transverse plane about the vertical axis. The vertical axis Transverse plane passes vertically through the body, allowing rotation of the body in an upright position. Vertical axis 52 837021_ch02.indd 52 02/02/16 5:09 PM 2 Movement analysis Key terms Sagittal plane Frontal plane: An imaginary line dividing the body vertically from front to back. Sagittal plane: An imaginary line dividing the body vertically into Frontal left and right sides.