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.
Door 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.
- 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.
Mechanical Advantage
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).
Second-Class Levers
Second-Class Lever
Second-Class Lever – A lever where the load is between the fulcrum and the effort, providing mechanical advantage (e.g., calf raise).
- In a Class 2 lever, the load is between the effort and the fulcrum.
- This type of lever always increases force but reduces the speed and range of motion.
- It is useful for tasks requiring a lot of force, such as lifting heavy objects.
- The calf raise is a common second-class lever in the body.
- In this movement, the ball of the foot serves as the fulcrum, the calf muscles generate the effort, and the body weight is the load.
Key Characteristics of Class 2 Levers:
- Load is positioned between the effort and fulcrum.
- Increases force but decreases speed and range of motion.
Movements that involve lifting or pushing heavy weights, such as pushing a wheelbarrow.
Second-class levers always operate at a mechanical advantage because the effort arm is longer than the load arm.
Mechanical Advantage
- Class 2 levers always provide a mechanical advantage, allowing for greater force output with less input force.
- The load is always closer to the fulcrum than the effort.
Class 2 levers are the most common type in the human body, especially for actions that require lifting or pushing heavy weights.
Third-Class Levers
Third-Class Lever
Third-Class Lever – A lever where the effort is between the fulcrum and the load, allowing greater speed and range of motion (e.g., bicep curl).
- In a Class 3 lever, the effort is located between the load and the fulcrum.
- This type of lever always increases speed and range of motion but requires more force to lift the load.
- Most of the human body’s movements use Class 3 levers, as they allow for quick and powerful motions.
- The bicep curl is a classic example of a third-class lever.
- The elbow joint acts as the fulcrum, the biceps provide the effort, and the weight in the hand represents the load.
Key Characteristics of Class 3 Levers:
- Effort is positioned between the load and fulcrum.
- Increases speed and range of motion but requires greater force to move the load.
Examples include quick, explosive movements like running or lifting light objects rapidly.
Baseball Throw Analysis:
- Shoulder joint: Fulcrum
- Arm muscles: Effort
- Ball: Load
- Third-class lever system enables high velocity
Mechanical Advantage
- Class 3 levers do not offer a mechanical advantage in terms of force instead, they increase the speed and range of motion.
- The effort is positioned between the fulcrum and the load, requiring more force to move the load.
- Think of a Class 3 lever as a fishing rod.
- The closer your hand (effort) is to the fulcrum (the reel), the faster and farther you can cast the line, but you need to apply more force to lift the fish (the load).
- Students often confuse the effect of mechanical advantage with speed or force.
- It’s important to remember that levers with mechanical advantage increase force, while those with reduced mechanical advantage increase speed or range of motion.
Levers inside the Body
- In the human body, bones act as levers, joints act as fulcrums, and muscles provide the effort.
- The arrangement of these levers enables us to perform various movements, from lifting objects to sprinting, with varying levels of force and speed.
- Most levers in the human body are third-class levers, which prioritize speed and range of motion over force.
Elbow Joint: The elbow joint acts as the fulcrum in a Class 3 lever when performing a bicep curl.
- Effort: The biceps exert the force to lift the weight.
- Fulcrum: The elbow joint.
- Load: The weight in the hand.
In this case, the effort is applied between the fulcrum (elbow) and the load (weight), resulting in a Class 3 lever, which increases the speed and range of motion at the expense of force.
- In sprinting, the leg uses Class 3 levers (such as in a knee extension) to generate quick, explosive movements.
- By increasing the speed at which the lower leg moves (due to the Class 3 lever), the athlete can increase stride frequency and speed.
- The human body often sacrifices mechanical advantage for greater speed and range of motion.
- This is why third-class levers are so common in our anatomy.
Lever outside the body
External levers include objects such as bats, rackets, and clubs, where the athlete applies force to one end of the lever, and the other end is used to strike or move a load (e.g., a ball or another object).
- Bat: In baseball or cricket, the bat is an external Class 3 lever, where the effort is applied by the hands, the fulcrum is at the bottom of the bat, and the load is the ball.
- Racket: In tennis or badminton, the racket is another Class 3 lever, where the effort is applied by the hands, the fulcrum is at the handle, and the load is the ball.
- Fishing Rod: In sports like fishing, the rod acts as a Class 3 lever, where the effort is applied by the fisher’s hand, the fulcrum is at the base of the rod, and the load is the fish at the end of the line.
- In baseball, when the batter swings the bat, the fulcrum is where the hands grip the bat, and the load is the ball.
- The effort is applied by the batter's hands.
- The bat is a Class 3 lever, providing speed and range of motion, allowing the batter to hit the ball with high velocity.
Lever Applications in Sports Techniques
Athletes can enhance their performance by understanding which lever class is most advantageous for a given movement:
- Class 2 levers are optimal for strength-based movements, such as lifting or pushing.
- Class 3 levers are used for speed and agility because they provide quick, wide-ranging movements (e.g., in sports like basketball, baseball, and sprinting).
Weightlifting Technique:
- Shorter arms advantage in bench press (reduced load arm)
- Longer arms advantage in deadlift (better floor reach)
- Technique modification can optimize leverage
Shorter arms may offer an advantage in weightlifting by reducing the distance the load must travel.
- How does understanding levers in the human body influence the design of sports equipment?
- Consider the ethical implications of using technology to enhance natural movement.
- Give an example of a Class 2 lever in the human body.
- Why is the calf raise an example of a second-class lever, and what is its mechanical advantage?
- If the effort arm is 30 cm and the load arm is 10 cm, what is the mechanical advantage of the lever?
- Explain how the elbow joint functions as a Class 3 lever.
- In a bicep curl, how does the lever system in the body contribute to movement?
