Movement Analysis: Levers, Planes and Axes

The body as a machine

When you move, your bones, joints and muscles work together like a set of simple machines, and movement analysis is the skill of describing that precisely. Every joint acts as a lever. A lever has three parts: the fulcrum, the fixed pivot; the effort, the force from the muscle; and the load, the weight being moved. Which of the three sits in the middle decides the lever class, first, second or third. Movement also happens in a plane, the flat direction it travels in, and around an axis, the line it turns about. And each joint has named actions, such as flexion and extension. This module teaches the three lever classes and mechanical advantage, the planes and axes, and the joint actions, so that you can take any sporting movement and describe exactly what is happening.

Words for movement

Learn what each of these means before you use it.

Planes against axes

These two go together but are not the same, and telling them apart is a common exam discriminator.

How to name a lever

Naming a lever class looks hard until you use one routine every time. Find the three parts first. The fulcrum is the joint. The effort is where the muscle pulls. The load is the weight being moved, often at the end of the limb. Then ask the only question that matters: which of the three is in the MIDDLE. Fulcrum in the middle is first class. Load in the middle is second class. Effort in the middle is third class, and that is the one you meet most in the body. Do not try to remember examples on their own; work out the parts, see which is central, and the class names itself.

Match the lever to its example

Which lever class?

In a bicep curl the elbow is the pivot, the bicep muscle pulls between the elbow and the hand, and the weight sits in the hand at the end. Which lever class is this?

• a third-class lever
• a first-class lever
• a second-class lever
• it is not a lever at all

Order how to find the lever class

Put the steps for working out a lever class in a sensible order.

• Find the fulcrum, which is the joint
• Find the load, the weight being moved
• Find the effort, where the muscle pulls
• Name the class from whichever part is in the middle

Spot the true movement facts

Tap the TWO statements that are true.

• A third-class lever has the effort in the middle and is the most common in the body
• Flexion is a movement that decreases the angle at a joint
• First-class levers are by far the most common in the human body
• A plane and an axis are two words for exactly the same thing

How many lever classes left?

There are 3 classes of lever: first, second and third. So far you have worked through 1 of them in detail. Subtract to find how many of the 3 are left to work through.

Complete the movement facts

A movement that decreases the angle at a joint, such as bending the elbow, is called _____. A movement that increases the angle at a joint, such as straightening the elbow, is called _____. Moving a limb away from the midline of the body is called _____. The lever class with the effort in the middle, the most common in the body, is the _____ class.

Analysing a bicep curl

Take one everyday gym movement, lifting a dumbbell in a bicep curl, and analyse it fully. Start with the lever. The elbow is the pivot, the bicep pulls a little way along the forearm, and the dumbbell sits out at the hand, so the pulling force is between the pivot and the weight, which makes it a third-class lever. Now the joint action. As the weight rises, the elbow closes and the angle at the joint gets smaller, which is one named action; as you lower it, the angle opens again, which is its opposite. Finally the plane and axis. The forearm swings forward and up, a movement in the plane that runs front to back, turning around the line that runs side to side through the elbow. Notice that you have described the same simple movement three ways, by lever, by joint action, and by plane and axis, which is exactly what a full analysis does.

Build the lever rule

Choose the words that complete the rule for naming a lever class.

Analyse the action

Read each case and choose the best answer, then think about why.

• A person rises onto their tiptoes, with the ball of the foot as the pivot and their body weight between it and the calf muscle. Which lever class is this?
• A gymnast performs a forward somersault, rotating forward around a line that runs side to side through the body. In which plane is this movement?
• A player raises their arm out sideways, away from the midline of the body. Which joint action is this?

Levers and joints

Select the TWO statements that are true.

• A first-class lever has the fulcrum in the middle, as when nodding the head
• Adduction is moving a limb towards the midline of the body
• A second-class lever has the effort in the middle
• Extension makes the angle at a joint smaller

Explain movement analysis

A friend is revising PE and cannot tell the lever classes apart or describe a movement properly. Explain how to analyse a movement, using the ideas from this module.

• Explain what the fulcrum, effort and load are in a lever
• Explain how you tell the three lever classes apart
• Explain the difference between flexion and extension
• Explain the difference between a plane and an axis of movement
• Finish by explaining how you would analyse one sporting movement of your choice