Overview
This lecture introduces the concept of levers in biomechanics, explaining how they function in the human body and outlining the three main types of levers with examples.
Introduction to Biomechanics and Levers
- Levers are rigid segments that rotate around a support point (fulcrum) when a force is applied.
- The human body uses levers, mainly bones as rigid segments, muscles as force, and joints as fulcrums.
- The way we position weights or our limbs changes the force required for movement.
Basic Structure of a Lever
- A lever has three parts: the fulcrum (support point), the resistance (load), and the force (effort).
- Movement in the body occurs when a force generated by muscles overcomes resistance using bones as levers.
Types of Levers
- There are three types of levers: first, second, and third class, based on the arrangement of fulcrum, force, and resistance.
- First-class lever: Fulcrum is between the force and resistance (e.g., seesaw, head nodding at the neck).
- Second-class lever: Resistance is between the fulcrum and force (e.g., wheelbarrow, calf raises at the ankle).
- Third-class lever: Force is between fulcrum and resistance (e.g., fishing rod, bicep curl at the elbow).
Examples in the Human Body
- First-class lever: Head and neck—atlas vertebra acts as fulcrum, neck muscles provide force, head’s weight is resistance.
- Second-class lever: Standing on tiptoes—ball of foot is fulcrum, body weight is resistance, calf muscles provide force.
- Third-class lever: Biceps curl—elbow is fulcrum, biceps provide force, weight in hand is resistance.
Preview of Next Topic: Moment Arm
- The moment arm (lever arm) affects how much force is required to lift a load.
- Changing the distance from the axis (fulcrum) changes the force needed.
Key Terms & Definitions
- Lever — a rigid structure that rotates around a fulcrum when a force is applied.
- Fulcrum — the pivot point or support on which a lever turns.
- Resistance — the load or weight the lever acts against.
- Force (Effort) — the input energy, usually from muscles, to move the lever.
- Moment Arm — the perpendicular distance from the fulcrum to the line of action of the force.
Action Items / Next Steps
- Watch the next video on the moment arm to deepen understanding of lever mechanics in the body.