Lever systems, examples of their use in activity and the mechanical advantage they provide in movement

Welcome to Movement Analysis: Lever Systems!

In this chapter, we are going to look at how the human body acts like a giant machine. When you kick a ball, lift a weight, or even just nod your head, your body is using lever systems. Understanding these helps us see how athletes can move faster or lift heavier loads with less effort. Don't worry if it sounds a bit like physics at first—we’ll break it down step-by-step!

1. The Three Parts of a Lever

Every lever system in the body is made up of three basic parts. You can remember them with the acronym FEL (like a tree that has 'fell' over):

• Fulcrum (F): This is the pivot point. In the human body, the joints act as the fulcrums.
• Effort (E): This is the force applied to move the lever. In our bodies, the muscles provide the effort when they contract.
• Load (L): This is the weight or resistance that needs to be moved. It could be the weight of a body part or a piece of equipment, like a shot put or a dumbbell.

Quick Review: The Basics

• Fulcrum = Joint
• Effort = Muscle contraction
• Load = Weight of the object/body part

2. The Three Classes of Levers

There are three types (or classes) of levers. The difference between them is simply which part is in the middle. Here is the easiest way to remember them: 1 - 2 - 3, F - L - E.

First Class Lever (F is in the middle)

The Fulcrum is in the middle, between the Effort and the Load. Think of a seesaw or a pair of scissors.
• Sporting Example: Moving your head to header a football. The joint where your head meets your neck is the fulcrum, your neck muscles provide the effort, and the weight of your head is the load.

Second Class Lever (L is in the middle)

The Load is in the middle. Think of a wheelbarrow.
• Sporting Example: Standing on your tiptoes to jump for a rebound in basketball. Your toes are the fulcrum, the weight of your body is the load in the middle, and your gastrocnemius (calf muscle) provides the effort at the back.

Third Class Lever (E is in the middle)

The Effort is in the middle. This is the most common lever in the human body.
• Sporting Example: A bicep curl. Your elbow joint is the fulcrum at one end, the bicep muscle pulls in the middle (effort), and the weight in your hand is the load at the other end.

The Ultimate Memory Aid: 123 - FLE

1st Class = Fulcrum in the middle
2nd Class = Load in the middle
3rd Class = Effort in the middle

3. Mechanical Advantage

Levers give us a "mechanical advantage." This basically means they help us move things more efficiently. To understand this, we need to look at two "arms" on the lever:

• Effort Arm: The distance from the Fulcrum to the Effort.
• Load (Resistance) Arm: The distance from the Fulcrum to the Load.

The Formula

You can calculate mechanical advantage using this formula:
\( \text{Mechanical Advantage} = \frac{\text{Effort Arm}}{\text{Weight (Resistance) Arm}} \)

High Mechanical Advantage (Second Class Levers)

In a second-class lever (like your ankle), the Effort Arm is longer than the Load Arm. This means you can move a very large load with relatively little effort.
• Benefit: You can lift your entire body weight just by using your calf muscles!
• Drawback: The movement is slow and the range of motion is small.

Low Mechanical Advantage (Third Class Levers)

In a third-class lever (like your elbow), the Load Arm is longer than the Effort Arm. This is actually a mechanical disadvantage in terms of force, but it's great for sport!
• Benefit: It allows for speed and a wide range of motion. This is why we can swing a tennis racket or kick a ball very fast.
• Drawback: You need more effort to move a smaller load.

Key Takeaway

Second class levers are for power (lifting heavy things).
Third class levers are for speed and distance.

4. Levers in Action: Sporting Movements

The exam will often ask you to link a specific lever to a movement at a joint. Here is a handy guide for the most common ones:

The Elbow (Flexion and Extension)

• Flexion (Bicep Curl): This is a Third Class Lever (Effort in the middle).
• Extension (Push-up or Tricep Extension): This is a First Class Lever (Fulcrum in the middle). Think of the elbow joint as the pivot, the triceps as the effort pulling on one side, and the arm as the load on the other.

The Ankle (Plantar and Dorsi-flexion)

• Plantar-flexion (Pointing toes/Standing on tiptoes): This is a Second Class Lever (Load in the middle). This is very efficient for lifting your body weight.

The Knee (Flexion and Extension)

• Flexion (Hamstring Curl): This is a Third Class Lever. The knee is the fulcrum, the hamstrings provide effort in the middle, and the lower leg is the load.

5. Common Mistakes to Avoid

• Mixing up the order: Always write down 123-FLE at the top of your exam paper to make sure you don't get them confused!
• Assuming all joints are the same: Remember that the class of lever can change depending on which muscle is working (the agonist). For example, the elbow is a 3rd class lever during a bicep curl, but a 1st class lever during a tricep extension.
• Forgetting the formula: Remember that Effort goes on top of the fraction for Mechanical Advantage.

Quick Review Box

• 1st Class: Header in football (F in middle).
• 2nd Class: Jumping/Tiptoes (L in middle). High power!
• 3rd Class: Bicep curl/Kicking (E in middle). High speed!
• Formula: \( \text{Effort Arm} \div \text{Load Arm} \)

Don't worry if this seems tricky at first! Just remember the 123-FLE rule and you will be able to work out any lever system the exam throws at you.