Levers in Biomechanics

Role in Movement: Leverage is crucial for efficient movement. Particularly significant for healthcare professionals like nurses, avoiding back injuries is paramount.
Back Injury Statistics: 38% of nursing staff experience disabling back injury or pain. Nursing jobs often rank among the highest for back injury risk, primarily due to patient movement.
Biomechanical Challenges: Moving patients presents biomechanical challenges, as individuals have awkward shapes that require awkward body positions to move them, leading to large forces in action. The biomechanics of the body either amplify or mitigate these forces via leverage.

Definition of Strength: Strength is defined as the body’s ability to apply and withstand forces.
Components of Strength:
- Ability to apply sufficient force to move, lift, or hold a weight (referred to as a load).
Definition of a Lever: A lever is a rigid object that facilitates moving a large load over a short distance or a small load over a greater distance.
Classes of Levers: Three classes of levers exist in the human body, with most being 3rd class levers.

Third Class Lever:
- Example: The forearm acts as a third class lever; the biceps muscle pulls on the forearm between the elbow joint (fulcrum) and the load (ball held).
- Illustration: The elbow joint forming a 60° angle while holding a 50 lb ball represents this lever in practice.

Components of a Lever:
- Lever: The forearm
- Effort: Biceps tension
- Fulcrum: Elbow joint
- Resistance: Weight of the object being moved (load)
Classes of Levers:
- First-Class Levers: Fulcrum is centered between effort and load (e.g., scissors, seesaw, pliers).
- Second-Class Levers: Load is positioned between fulcrum and effort (e.g., nutcracker, wheelbarrow, bottle opener).
- Third-Class Levers: Effort is positioned between fulcrum and load (e.g., fishing rod, pair of tongs, stapler).

First-Class Lever Example: The top neck joint acts as the fulcrum with neck muscles providing input force to tilt the head back.
Second-Class Lever Example: The ball of foot is the fulcrum that uses calf muscles, acting as the effort to raise the body.
Third-Class Lever Example: The elbow serves as a fulcrum where the biceps muscle acts as the effort to lift the arm.

Torque Principles: The effort and resistance create torques that work to rotate the lever. To move or hold a load, the torque generated by effort must counterbalance the torque induced by the load.
Factors Influencing Torque:
- Distance from the pivot at which force is applied is essential.
- Effort Arm: The distance from the fulcrum to the point where the effort is applied.
- Resistance Arm: The distance from the fulcrum to where load is applied.
Torque Balance Equation: The effort and the load torque ratios are equal to their respective arms' ratios:
ext{Torque}{ ext{effort}} = ext{Torque}{ ext{load}}

Composition of Levers in the Body:
- Bones: Serve as lever arms.
- Joints: Function as pivot points (fulcrums).
- Muscles: Provide effort forces for movement.
Mechanical Advantage: Lever systems allow small forces to impart large movements, crucial for efficient biomechanics.
Range of Motion: Lever systems enable large movement amplification with small muscle contractions resulting in significant movements further out (e.g. kicking a ball).

Third Class Levers:
- Advantage: Increases range of motion (e.g., small bicep contraction results in significant hand movement).
- Disadvantage: Requires a larger effort to hold smaller loads (e.g., bicep tension surpassing weight of the object held).
Second Class Levers:
- Advantage: Requires smaller effort to move larger loads (e.g., calf muscle can lift entire body weight).
- Disadvantage: Shorter range of motion than effort provided (calf muscle contraction compared to heel lift).
First Class Levers:
- Advantage: Can provide mechanical advantage or enhance range of motion.
- Disadvantage: Effort requirements can exceed load weight, leading to mechanical disadvantage in specific scenarios.

Lever Class	Advantage	Disadvantage
Third Class	Increases range of motion	Larger effort required for smaller load
Second Class	Smaller effort can lift larger load	Load moves shorter distance than effort
First Class	Load moves farther than the effort	Requires larger effort for smaller load

Overview of Lever Functionality: Each lever class presents unique advantages and disadvantages, influencing their application in human biomechanics. Lever systems are fundamental for understanding movements in nursing, sports, and daily activities.