EXSC 440- Levers

What are the three parts of the lever?

• Fulcrum

• Load

• Effort

What is the fulcrum?

-The point of axis or rotation

The pivot point

What is the load?

The object that is being moved

Sometimes called the resistance force

What is the effort?

The input force used to move the load

Sometimes called the force

What is a first class lever?

The fulcrum is always in the middle.

What is a second class lever?

The resistance will always be in the middle.

What is a third class lever?

The effort is always in the middle.

Examples of first class levers in our bodies

• Atlanto-axial joint in flexion/extension

Examples of second class levers in our bodies

• Ankle joint during a calf raise

• Push up (full-body lever)

Examples of third class levers in our bodies

• Knee during open chain extension

• Bicep curl

What is a full body lever?

• Resistance/load is usually body weight.

• Resistance/load is applied at the center of gravity (near belly button)

• Effort will be from muscles near the main/moving joint.

What is a joint specific lever?

• Fulcrum is typically the joint center. 

• Resistance/load is typically the weight of the body segment or a held weight.

• Effort comes from a specific muscle and is applied at its attachment point.

What is mechanical advantage?

A measure of force amplification. How effectively a system converts input force (effort) into output force (load).

MA = Effort Arm/Resistance Arm

What advantage is there when you give effort a short lever arm and resistance a long lever arm?

TORQUE

What advantage is there when you give effort a short lever arm and resistance a long lever arm?

DISTANCE/VELOCITY

What is the mechanical advantage of a first class lever?

Has potential to have either advantage because arms are the same length.

What is the mechanical advantage of a second class lever?

FORCE- because the effort arm is longer than the resistance.

What is the mechanical advantage of a third class lever?

ROM and SPEED- because the resistance arm is longer than the effort.

What is the mechanical advantage found throughout the human body?

We are built for ROM advantages and speed of movement with relatively light resistances because we have short effort arms and long resistance arms. We are NOT built for force advantages.