ANATOMICAL THIRD-CLASS LEVERS Flashcards
levers
A lever is a rigid bar that allows the application of either increased force and/or speed.
what are the common parts?
- an axis (point of rotation) A
- a resistance (load to be overcome) R
- a force (the point where the force is applied) F
how are levers classified?
Levers are classified depending on the location of the axis, force and resistance in relation to each other. They are categorised as either first-class, second-class or third-class levers.
- A first-class lever always has the axis in the middle, between the force and the resistance.
- A second-class lever always has the resistance in the middle.
- A third-class lever will always have the force in the middle.
The most common lever found in the body is the third-class lever.
first class lever
the resistance and the force are on either side of the axis
second class lever
the resistance is between the force and the axis
third class lever
Third-class levers are always built to amplify speed. They always have the force between the axis and the resistance.
- A good example of a third-class lever in the body is the upward phase of a bicep curl. The elbow joint is the axis (joints are always axes), the force is where the bicep muscles attach to the radius and ulna, and the resistance is the weight in hand
- Whenever we kick a ball or strike an object with a hand or racquet the resistance is the weight of the object being struck and therefore is at one end of the lever system
- ALL THIRD CLASS LEVERS HAVE A MECHANICAL ADVANTAGE LESS THAN ONE. However a greater force is required, but only over a small distance. This increases ROM and angular speed
The joint = axis
Muscle = provides the force
What you want to move = resistance
increase lever length
= increased resistance
= more force required to swing bat or racquet
= increased range of motion
mechanical advantage
Mechanical advantage is a measure of how much a lever amplifies force.
- A lever with a mechanical advantage greater than 1 (>1) will increase force (ARF).
- A lever with a mechanical advantage equal to 1 is balanced between speed and force.
- A lever with a mechanical advantage less than 1 (<1) will increase speed (AFR).
The formula is:
Mechanical advantage = force arm/ resistance arm
If the mechanical advantage of a lever is less than one, this means it is a speed magnifier. ll third-class levers are speed magnifiers because they all have longer resistance arms than force arms. The longer the resistance arm and the further below 1 the mechanical advantage is, the greater the speed that can be produced by the lever due to the greater range of motion at the end of the longer lever compared to the shorter one.
