Movement Analysis

levers

First, second and third class levers

Levers in our body are formed from bones, joints and muscles.

There are four parts to a lever – lever arm, pivot, effort and load. In our bodies:

bones act as lever arms
joints act as pivots
muscles provide the effort forces to move loads
load forces are often the weights of the body parts that are moved or forces needed to lift, push or pull things outside our bodies.

Levers can also be used to magnify movement, for example, when kicking a ball, small contractions of leg muscles produce a much larger movement at the end of the leg.

Levers are able to give us a strength advantage or a movement advantage but not both together.

Types of levers

Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged.

First Class lever

For the First Class lever the pivot lies between the effort and load. A see saw in a playground is an example of a First Class lever where the effort balances the load.

First Class lever – Sporting example - header in football

This pivot exists in the place where your skull meets the top of your spine. Your skull is the lever arm and the neck muscles at the back of the skull provide the force (effort) to lift your head up against the weight of the head (load). When the neck muscles relax, your head nods forward.

Second class lever

the load is in the middle between the fulcrum and the effort.

Second Class lever – Sporting example - Plantar flexion

This type of lever is found in the ankle area. When standing on tiptoe, the ball of the foot acts as the fulcrum, the weight of the body acts as the load and the effort comes from the contraction of the gastrocnemius muscle. This second class lever is used when taking off for a jump or pushing against the blocks in a sprint start.

Third class lever

the effort is in the middle between the fulcrum and the load.

Third Class lever – Sporting example - Bicep curl

During a biceps curl, the fulcrum is the elbow joint, the effort comes from the biceps contracting and the resistance is the weight of the forearm and any weight that it may be holding.

To recall the order of the levers use the term 'FLE' - this will help you to remember which part of the lever is in the middle.

First class lever - Fulcrum is in the middle.

Second class lever - Load is in the middle.

Third class lever - Effort is in the middle.

analysis of levers - mechanical advantage or disadvantage?

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:

If the effort arm is longer than the resistance arm, less force is required to move the resistance.

Second Class 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:

If the effort arm is shorter than the resistance arm; more force is required to overcome the resistance.

Third Class 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.

First Class 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.

First Class 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.

First Class lever with MECHANICAL ADVANTAGE which amplifies force

First class level with MECHANICAL DISADVANTAGE which amplifies speed

planes and axis

All body movements occur in different planes and around different axes.

A plane is an imaginary flat surface running through the body.

An axis is an imaginary line at right angles to the plane, about which the body rotates or spins.

axis of rotation

There are three axes of movement around which the body or body parts rotate:

Frontal axis - this line runs from left to right through the centre of the body. For example, when a person performs a somersault they rotate around this axis.

Sagittal axis - this line runs from front to back through the centre of the body. For example, when a person performs a cartwheel they are rotating about the sagittal axis.

Vertical axis - this line runs from top to bottom through the centre of the body. For example, when a skater performs a spin they are rotating around the vertical axis.

planes of movement

There are three planes of movement: A Plane is an imaginary flat surface running through the body.

Movements are parallel to the plane in which they take place.

Sagittal Plane

The Sagittal plane passes through the body front to back, so dividing it into left and right. Movements in this plane are the up and down movements of flexion and extension

Frontal Plane

The frontal plane divides the body into front and back. Movements in this plane are sideways movements, called abduction and adduction

Transverse Plane

This plane divides the body into top and bottom. Movements in this plane are rotational in nature, such as internal and external rotation, pronation and supination

relationship between planes and axis

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