400882 Introduction to Biomechanics - Levers

What is a lever?

Lever is a rigid bar - free to move about point of suspension called a fulcrum (F) or axis (A)

Name the 3 main features found in a lever system.

• Fulcrum (axis F)

• Effort (E)

• Load (L) or resistance (R)

Name and describe (with the aid of diagrams) the 3 main types / classes of levers systems.

• 1st class lever (E A L) → see saw → skull on top of neck (E muscle, A atlas/axis, L head) few in human body

• 2nd class lever (A L E) → wheelbarrow → standing on toes

• 3rd class lever (L E A) → spade or fishing rod in belt cup → bicep curl

• 4th class lever (torsional) load above fulcrum → causes rotation - not very common type

Which is the most common lever type in the human body?

Third class lever is the most common in the human body.

What two mechanical advantages can lever systems provide?

Force and speed

What effect is produce by a lever system where the resistance arm is greater than the force arm?

Speed advatage

What effect is produce by a lever system where the resistance arm is shorter than the force arm?

Force advantage

What mechanical advantage does a second class lever always have?

A force advantage

What mechanical advantage does a third class lever always have?

Speed advantage

List four things that can affect the joint torques produced from muscle contractions.

• Lever structure and angle of pull on the bone

• Length of the muscle affects contractile force

• Type of muscle fibre (e.g. pennate/parallel).

• Velocity of contraction

• As joint changes, muscle length also changes