levers

Fulcrum

The fixed pivot point of a lever; in the human body, this is the joint.

Lever Component: Effort

The force applied to move the lever; in the human body, this is the muscular contraction (applied at the muscle's insertion point).

Lever Component: Load (Resistance)

The weight or resistance that the lever system must move (e.g., body weight, a dumbbell, or a ball).

Mnemonic for Lever Classes

123 FLE (1st class = Fulcrum in middle, 2nd class = Load in middle, 3rd class = Effort in middle).

First-Class Lever (F in middle)

Fulcrum is between effort and load. Example: Neck extension (Head = Load, Neck = Fulcrum, Muscles = Effort).

Second-Class Lever (L in middle)

Load is between fulcrum and effort. Example: Plantar flexion (Ball of foot = Fulcrum, Body weight = Load, Gastrocnemius = Effort).

Third-Class Lever (E in middle)

Effort is between fulcrum and load. Example: Bicep curl (Elbow = Fulcrum, Bicep insertion = Effort, Weight in hand = Load).

Definition: Effort Arm

The distance between the fulcrum (joint) and the point of effort (muscle insertion).

Definition: Resistance/load Arm

The distance between the fulcrum (joint) and the center of the load (weight).

Formula: Mechanical Advantage

Mechanical Advantage = Effort Arm Length ÷ Resistance Arm Length.

Mechanical Advantage (MA > 1)

Occurs when the effort arm is longer than the resistance arm. Found in Second-Class levers.

Benefit of Mechanical Advantage

Allows a large load to be moved with relatively small effort (force efficiency).

Mechanical Disadvantage (MA < 1)

Occurs when the resistance arm is longer than the effort arm. Found in Third-Class levers.

Benefit of Mechanical Disadvantage

Allows for a greater range of motion and high speed of movement at the end of the lever.

Class 1 Lever: Advantage/Disadvantage

Can provide both depending on the position of the fulcrum. If fulcrum is near the load, it has an advantage; if near effort, a disadvantage.

Most Common Lever in the Body

Third-Class Lever (designed for speed and range of motion rather than moving heavy loads).