Levers of the Musculoskeletal System

Flashcards on Levers of the Musculoskeletal System

Axis of Rotation

In the center of any joint which we are taking interest in.

Rigid levers

Act around the axis of rotation.

External Resistances

By mass of the levers (points straight down in accordance with gravity)

Muscle Force Vector (effort force vector)

Acts in the opposite direction to external resistance.

Mechanical advantage

Effort arm / Resistance arm

Mechanical Advantage of the Plantar-flexors

A human lever system with MA > 1; Effort arm > Resistance arm SO Plantar-flexors can lift the heels while generating less than body weight forces.

Most human levers

Magnify Speed and range.

Levers & Torque

Force, at any point along a lever, generates torque (the rotational equivalence of force), a vector quantity.

Torque

Force x Distance

Torque Sign Convention

Clockwise torques are negative, anticlockwise ones are positive.

Levers that are not always horizontal

Extend the force vector to create a right angle triangle and calculate dra using trigonometry.

Assuming Equilibrium

Smaller lever = More force required

Levers and Strength

Larger muscles can generate more force but muscle ‘cross-sectional area’ is not the only factor that influences ‘strength.

Levers and Shopping Bags

Moving the shopping bags closer to the joint axis of rotation makes you require less force to carry the object as the lever is shorter.

Frot

Generates torque

Fnonrot

Generates a stabilising force