Levers in movement and sport
Lever
A lever is a rigid structure that rotates around a fixed point called the fulcrum. Levers are used to move a load (resistance) by applying an effort (force). The relative positions of the fulcrum, load, and effort determine the type of lever and its mechanical advantage or disadvantage.
- Levers are rigid rods that rotate around a fulcrum (pivot point) when a force is applied.
- The purpose of a lever is to move a load (or resistance), which could be a weight or the force of an object needing movement.
In the human body, bones act as levers, joints as fulcrums, and muscles provide the effort.
Parts of a Lever
A lever consists of three main components.
1. Fulcrum
- The fulcrum is the fixed point around which the lever rotates or pivots.
- It is the axis of movement and does not move itself.
- In human anatomy, joints typically serve as the fulcrum in lever systems.
- In a seesaw, the fulcrum is the pivot point in the middle.
- In the human body, the elbow joint acts as the fulcrum in many upper limb movements.
2. Effort
- The effort is the force applied to the lever to move the load.
- In the body, this force comes from muscle contraction.
- The effort is applied at a point on the lever, and it is the key to generating the force necessary for movement.
- In a bicep curl, the bicep muscle contracts to apply effort in lifting the weight.
- The effort is applied at the forearm, which then moves the load (the weight).
3. Load
- The load is the resistance or the weight being moved by the lever.
- In the body, the load could be an external object, like a dumbbell, or a body part, such as the forearm when lifting an object.
During a calf raise, the weight of the body (as the load) is lifted by the action of the calf muscle (the effort), with the ball of the foot acting as the fulcrum.
ExampleDoor operation demonstrates lever principles:
- Fulcrum: Hinges
- Effort: Push/pull on handle
- Load: Door weight
- Moment arms: Door width and handle position
Mechanical Advantage
Mechanical Advantage
The ratio between effort and load that determines a lever's efficiency
- The mechanical advantage of a lever refers to its ability to amplify the force applied to it.
- This is determined by the ratio of the lengths of the effort arm to the load arm.
- The longer the effort arm, the greater the mechanical advantage, making it easier to move a heavy load with less force.
Formula for Mechanical Advantage
The mechanical advantage of a lever is given by the formula:
Mechanical Advantage (MA) = Length of Effort Arm / Length of Load Arm
- Effort arm: Distance from the fulcrum to the point where the effort is applied.
- Load arm: Distance from the fulcrum to the point where the load is applied.
In a second-class lever, the effort arm is longer than the load arm, giving the lever a mechanical advantage that makes lifting easier, despite using less force.
Note- Higher MA: The effort required to move a load is reduced, but the range of motion and speed of movement are also reduced.
- Lower MA: The effort increases, but the range of motion and speed increase, making the movement more dynamic and explosive.
The Three Classes of Levers
Levers are classified into three types based on the relative positions of the effort, fulcrum, and load:
- First-Class Levers: Fulcrum is between the effort and load.
- Second-Class Levers: Load is between the fulcrum and effort.
- Third-Class Levers: Effort is between the fulcrum and load.
First-Class Levers
First Class Lever
First-Class Lever – A lever where the fulcrum is between the effort and the load, like a seesaw (e.g., neck extension).
- In a Class 1 lever, the fulcrum is located between the effort and the load.
- This arrangement can either increase the force or the speed of the movement, depending on the relative positions of the effort and load.
- The neck joint in the human body, where the atlas vertebra acts as the fulcrum, the neck extensor muscles provide the effort, and the weight of the head is the load.
- The effort and load can be adjusted to balance the head or to raise it.
Key Characteristics of Class 1 Levers
- Fulcrum is positioned between the effort and load.
- Can provide a balance between force and speed.
- Can change the direction of the force (e.g., tilting the head).
First-class levers can provide either a mechanical advantage or disadvantage, depending on the relative lengths of the effort arm and load arm.
Mechanical Advantage
- A Class 1 lever can either have a mechanical advantage or a disadvantage, depending on the relative positions of the effort, load, and fulcrum.
- When the effort arm is longer than the load arm, the lever has a mechanical advantage (increases force).
Class 1 levers are less common in the human body but are seen in some joints (like the neck and the triceps during a push-up).
