Kinetics: Levers and Mechanical Advantage

These flashcards cover key terms and concepts related to biomechanics, specifically focusing on levers, mechanical advantage, and the relevant functions of muscles in the human body.

First Class Lever

Axis of rotation is located between the opposing forces.

Second Class Lever

Rare in the human body; resistance is between the axis of rotation and effort.

Third Class Lever

Most common lever in the human body; effort is between the axis of rotation and resistance.

Mechanical Advantage

The ratio of the force produced by a machine to the force applied to it.

High Mechanical Advantage

Greater than 1; force amplifier prioritizing strength.

Low Mechanical Advantage

Less than 1; motion amplifier prioritizing speed and range of motion.

Fulcrum

The pivot point around which a lever rotates.

Effort

The force applied to a lever to produce movement.

Resistance

The external load that opposes the effort in a lever system.

Torque

The rotational force applied at a distance from the fulcrum.

Moment Arm

The perpendicular distance from the line of action of the force to the axis of rotation.

Muscle Force

The force produced by muscle contractions to create movement.

Internal Moment Arm (IMA)

The distance from the muscle's line of action to the axis of rotation.

External Moment Arm (EMA)

The distance from the load's line of action to the axis of rotation.

Gastrocnemius

A muscle involved in heel raises, exemplifying a second class lever.

Biceps

A muscle responsible for elbow flexion, an example of a third class lever.

Hamstrings

Muscles involved in knee flexion, also operating as third class levers.

Leverage

The mechanical advantage gained by using a lever.

Torque Equation (High Mechanical Advantage)

Effort (force applied) multiplied by IMA equals torque.

Torque Equation (Low Mechanical Advantage)

External force (resistance) multiplied by EMA equals torque.

Compression Forces

Forces that push or squeeze tissues together commonly in mechanical systems.

Shear Forces

Forces that act parallel to a surface, often seen in muscles operating at < 1 mechanical advantage.

Effort Arm

The length of the lever arm from the fulcrum to the point where the effort is applied.

Resistance Arm

The length of the lever arm from the fulcrum to the point where the resistance acts.

See Saw

An example of a first class lever with the fulcrum in the center.

Elbow Extension

An example of a first class lever, where the fulcrum is closer to the effort.

Cranial Extensors

Muscles that hold the head upright, functioning as a first class lever.

Effort Direction

The direction in which the effort is applied in a mechanical system.

Resistance Direction

The direction in which the resistance acts in a lever system.

Axis of Rotation (AoR)

The point around which the lever rotates; crucial in defining leverage.

Speed vs. Strength

Trade-off in lever systems; high m.a. prioritizes strength, low m.a. prioritizes speed.

Body Weight (BW)

The external load considered in calculating mechanical advantage and lever systems.

Muscles and Leverage

Muscles build tension to produce greater forces than external resistance.