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LEVER SYSTEMS
LEVER SYSTEMS
In order to complete sports movements bones must be moved so forces can be applied to the floor or the sports equipment we use. Movements are possible because of joints and muscular contractions. They operate in lever systems. This is where forces applied at one point of a bar (or bone in our case) move a resistance at second point, about a fulcrum or pivot. In our bodies, the muscles exert forces on the bones, moving one or both of these bones at the pivot point and these forces can be applied to other objects that they are in contact with (e.g. the floor, when we run & jump; or a rower pulling the oar against the water).
In a lever system there are three factors that must be considered.
1. Fulcrum: this is point at which the lever hinges or rotates.
2. Effort: this is the contraction of the muscle that pulls the bone, exerting a force.
3. Resistance: this is the load or mass the lever system must overcome. For example in lifting a weight during a bicep curl the resistance will be the mass of the weight and the lower arm, overcoming the force of gravity.
There are three classes of levers, called 1st, 2nd, and 3rd order. Levers are classified depending on the location of the fulcrum, resistance and load.
An easy way to remember the classes of lever is by using the rhyme, ‘1,2,3 –F, R, E’ with the letters F, R and E relating to ‘Fulcrum, Resistance and Effort’. The is to remember what is in the middle for example in a class 1 lever the Fulcrum is in the middle. Whilst in class 2 the Resistance is in the middle and in class 3 it is the Effort.
In class 1 levers the Fulcrum lies in the middle between effort and resistance If you think of a ‘see-saw’ in the local park, this is an example of class I lever system. If a friend sits on one end of the see-saw then you need usually lift them up by applying a force to the lever arm by sitting on the other side (of the fulcrum). Class I levers are not very common in the human body and the two main locations in the body are the neck and at the elbow (role of the triceps in extension at the elbow joint).
In class 2 levers the fulcrum and effort lie at opposite ends of the lever arm with the Resistance in the middle. An example of this is a wheelbarrow, where the fulcrum is where the wheel touches the ground, effort is applied to the handles to lift an object, maybe a collection of rocks, which are located in the barrow in the middle of the lever system. Class II levers are unusual in the human body and the most prominent example is the role of the gastrocnemius in calf raises.
In class 3 levers the fulcrum and resistance lie at opposite ends of the lever arm with the Effort in the middle. Class III levers are very common in the body and the actions at the hip, shoulder, knee and elbow (apart from the example shown above) are usually this type. An example is the bicep curl where the dumbbell is lifted by contracting the Bicep which is inserted on the radius and ulna (lever arm), between the dumbbell and the elbow (fulcrum). This lever system is good for;
- Kicking – so the knee and hip joints operate using this lever system,
- Throwing – so the shoulder joint operates using this lever system.
ANALYSIS OF LEVERS
ANALYSIS OF LEVERS
Key Terms
Key Terms
Effort Arm: the distance between the point of the application of effort and the fulcrum, usually where the muscle attaches to the bone.
Resistance Arm: the distance between the point of resistance or load and the fulcrum
Mechanical Advantage:
Mechanical Advantage:
If the effort arm is longer than the resistance arm, less force is required to move the resistance.
Class III levers are advantageous for applying large amounts of force but they are not good for accelerating objects quickly. They amplify force in the movement.
Mechanical Disadvantage:
Mechanical Disadvantage:
If the effort arm is shorter than the resistance arm; more force is required to overcome the resistance.
Class III levers are not advantageous for applying large amounts of force but they are good for accelerating objects quickly. They amplify the speed of the movement.
Class I levers can be a mechanical advantage or disadvantage. It is a mechanical advantage if the length of the effort arm is larger than the length of the resistance arm.
Class I levers can also be a mechanical disadvantage, when the length of the resistance arm is longer than the length of the effort arm.
If asked to analyse this system in an exam question you need to look at where fulcrum is positioned, if it is closer to the point of effort then there is a mechanical disadvantage and therefore is good for amplifying speed. If the fulcrum is positioned closer to the point of resistance then there is a mechanical advantage and it amplifies force.
In this example the Fulcrum is where the oar connects and pivots on the side of the boat. Does this produce an advantage or disadvantage?
Work out where the Fulcrum is in this example and if it produces an advantage or disadvantage.
PLANES AND AXES
PLANES AND AXES
Measurements of the body and descriptions of movements are described in three different dimensions. The use of ‘planes’ and ‘axes’ reduces the need for long and ‘wordy’ descriptions of movements and measurements. There are three imaginary planes and three axes of rotation.
A plane is the direction that movement happens in. An Axis is the line which movement rotates around.
Each plane is associated with an axis and these are the linked in the following manner:
- Sagittal plane and transverse axis
- Frontal plane and frontal axis
- Horizontal plane and longitudinal axis
Most movements in sport occur in the sagittal plane (and therefore around the transverse axis), skills that involve movement forwards or backwards occur in this plane for example a gymnast completing a forward roll or a hurdler running towards the first hurdle.
Plane A =Sagittal plane and Axis C = transverse axis
Plane C = Frontal plane and Axis B = frontal axis
Plane B = Horizontal plane and Axis A = longitudinal axis
Not an example you should use in the exam, but the players in table football, exemplify how rotation of the transverse axis will move the person or object through the sagittal plane.
Remember our little Andy Panda acronym!
Remember our jelly baby 'murder' in lesson guys!
Planes
A plane is an imaginary flat surface along which a movement takes place. The three planes of movement include:
o Sagittal Plane – separates the left and right sides of the body
o Frontal Plane – separates the front and back sides of the body
o Transverse Plane – separates the top and bottom parts of the body
Tips: Imagine that you have a very thin wall that is separating two halves of the body (i.e., left and right, front and back and top and bottom). Now envision the full length of the body part gliding along the wall throughout the entire movement, from start to finish.
AXES
An axis is an imaginary line about which the body or limb rotates. The three axes of movement include:
o Frontal Horizontal Axis – invisible line that travels from left to the right side of the body
o Vertical Axis – invisible line that travels from the top of the head to the bottom of the feet
o Sagittal Horizontal Axis – invisible line that travels from the front to the back side of the body
Tips: Imagine a steel rod running through the joint (i.e., left to right, top to bottom and front to back) and your limbs rotating around that joint. It is similar to a bicycle wheel that rotates around a narrow axle. The axle represents the axis or rotation and the wheel represents the plane along which the limb moves.
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