biomechanics Flashcards
biomechanics
The mechanical concepts applied to the human body and function
Includes the forces and the motion produced
force
Force = magnitude of push or pull action (F = Mass x Acceleration)
scalar
Scalar = describes only magnitude (how much) (i.e., ounces, grams, kilos)
vector
Vector = Measure of Magnitude (how much) and direction (of the push/pull)
Force is a Vector
mass
The amount of matter a body contains
How big something is
kinetics
Kinetics describes what causes motion
torque
Torque = force that produces rotation around an axis
ex) a hammer pulling a nail out
ex) doing a bicep curl
friction
Friction = force between two surfaces. Attempts to prevent motion of one surface over another
ex) a runners shoes create friction
velocity
Velocity = force + speed
law of inertia
Law of Inertia = an object in motion wants to stay in motion, an object at rest wants to stay at rest.
Need to generate enough force to get the object out of state of inertia
The greater the mass, the more force is needed to change the inertia
law of inertia
Objects as rest will stay at rest until force is applied.
Objects in motion will stay in motion until force is applied.
Ball Example
Seat belt example
law of acceleration
Law of Acceleration = the amount of acceleration (increasing speed/velocity) depends on the strength of the force applied to the object.
The amount of acceleration is proportionate to the amount of force applied.
The greater the mass, the more force needed to achieve the same acceleration as something with a smaller mass
Acceleration
Any change in velocity of an object
Kick a ball and see how far it travels.
Kick it twice as hard and it should go twice as far.
When the ball starts moving, it is accelerating.
If you were to kick it even harder, it would travel proportionately farther.
More force= more acceleration proportionate to that force
The amount of acceleration depends on…
The amount of acceleration depends on the strength of the force applied.
acceleration and direction
Acceleration can also deal with change in direction.
Force is needed to change direction.
Change in direction depends on the force applied (ie amount of force and direction of force)
If you were to apply the same force to two objects of differing mass, the object with the greater mass will…
If you were to apply the same force to two objects of differing mass, the object with the greater mass will accelerate less.
Acceleration is proportionate to the mass of an object
Law of Action-Reaction
Law of Action-Reaction = for every action, there is an equal and opposite reaction
Sources of Forces
Internal: --Muscle contraction --Ligament restraint --Bony support External: --Gravity --Resistance --Friction
Important to remember these three characteristics about force
Important to remember these three characteristics about forces
–Magnitude (vector)
–Direction (vector)
–Point of application
A force is a push or a pull and movement is caused when one force becomes greater than another.
linear forces
Different than linear MOTION (rectilinear and curvilinear)
Linear forces are still in a straight line
types of linear forces
parallel forces
concurrent forces
resultant forces
parallel forces
Parallel forces: occur in the same plane in the same or opposite direction (three point splint)
concurrent forces
Concurrent forces
Two or more forces acting on a common point but in different directions
resultant force
Resultant force
Effect of concurrent forces
force couple
Force couple: forces occurring in equal and opposite directions
Rotary Force = Torque
Force that produces movement around an axis
Equals the product of the force magnitude and the length of the moment arm
axis
The pivot point
In people, in most cases this is the joint
resistance
Is what the lever system is attempting to move or lift
It is counterbalanced by force
Example
With exercise we would consider this the weights.
force
The primary force behind the lever system.
This is what makes the lever go into action and counter balances the resistance.
In people, this would be the muscles contracting. – the force is applied at the INSERSTION!
ARF
A Axis: Joint
R Resistance: Weight
F Force: Muscle
types of Levers
Levers
First class
See Saw
Second class
Good for power
Wheelbarrow
Third class
Good for speed & distance
Screen Door
how to tell the difference between the different levers
If A is in the Middle = First Class
If R is in the Middle = Second Class
If F is in the Middle = Third Class
first class lever
First Class levers Few in the body Head on neck Axis in the middle Resistance on one end Force on the other end See saw
an ex of a first class lever in the body
• Relax your neck so that your head drops slowly forward.
• The head is a heavy object—about 4.5 kilograms and acts as the resistance.
• Your head drops forward when you relax your neck because your head and neck work like a first-class lever.
• The axis is at the top of the neck
The muscles in the neck provide an input force that allows you to raise your head.
• When you relax these muscles, gravity causes your head to go forward.
second class levers
Second Class Levers Best for power Few in the body Axis on one end Resistance in the middle Force on the other end Brachioradialis
second class lever in the body
Plantar flexors lifting the body where the metatarsals are the axis, the resistance is the weight of the body pushing down, and the force is the muscle contraction pulling up.
Brachioradialis – axis =elbow,
resistance = weight of forearm
force = insertion of the muscle
third class levers
Third Class Levers
Most common in the body
Best for distance and speed (aka ROM)
Biceps
what class of levers is the bicep?
Biceps ( 3rd Class)
With concentric contraction, where elbow is axis, resistance is weight of the hand, and force is contraction of bicep, pulling the hand back up
Biceps (2nd Class)
With eccentric contraction, where elbow is the axis, weight of the hand is the force, and the resistance is the bicep pulling upward.
2nd vs 3rd class levers
Biceps is a third class lever
Due to location of insertion on
the proximal radius.
As the biceps contracts, it applies
the force to the forearm.
Resistance is distal forearm and
Hand (and whatever you put in
your hand)
Brachioradialis is a second class lever.
Due to the insertion on the distal radius
In this case, the forearm is the resistance,
and the distal forearm is where the force is
applied.
What Factors Cause Classes to Change
Application of resistance
–Brachioradialis can be third class if you put a weight in
the hand.
Direction of movement in relation to gravity.
–Concentric movement against gravity is typically third
class lever
–Eccentric movement with gravity is second class lever
–Biceps example
Mechanical Advantage = ?
Mechanical Advantage = Leverage
MA = FA / RA
what are second class levers designed for? what are third class levers designed for?
Second class levers designed for power Third class levers designed for speed and distance Important to know for MMT, transfers, equipment modifications
mechanical advantage
Defined as the ratio between the force arm and the resistance arm.
A shorter force arm requires more force
A longer force arm requires less force
Can apply to therapeutic exercise
Airsplint example
Applies to MMT – we want to give the muscle the best possible advantage.
Shoulder example
