Biomechanics CH 8 Flashcards
Statics
deals w/ factors associated w/ non moving or nearly non moving systems
Dynamics
Moving systems divided into kinetics & kinematics
Kinetics
forces that cause systems to move
Kinematics
the time, space, and mass aspects of a moving system
Osteokinematics
refers to bone - joint movement
ie- flexion, extension
Arthrokinematics
joints surfaces move in relation to each other
ie- roll, spin, glide, slide
Force
a push or pull action that can be represented as a vector
Vector
a quantity that can have both magnitude and direction
ie- pushing a wheelchair at a certain speed & in a certain direction
Velocity
is a vector that describes speed and is measured in units such as feet per second or miles per hour
Biomechanics
The principles of mechanics as applied to the structures & function of the body
Magnitude
amount or size of the force applied on the object
What determines the magnitude of muscular force?
The number & size of muscle fibers that are contracting
What is a branch of physics studying and analyzing forces and motion produced by their actions
Mechanics
Scalar
a quantity that describes only magnitude
What are common scalar terms
length, area, volume, and mass
Mass
the amount of matter a body contains
Inertia
the property of matter that causes it to resist any change of its motion in either speed or direction
What is the tendency of force to produce force around an axis?
Torque
What are two simultaneous functions of movement?
Stabilization and movement functions
Internal forces
forces exerted on the body
Difference or changes in the shape of the body
Muscle contraction generates force, ligamentous restraint, or bony support
External forces
Outside forces causing displacement of body
Weight or gravitational forces
ie- gravity, wind, water, friction, forces acting on the body
Shear force
component force that is parallel to the surface
The force has an action line in the direction of the attempted movement
Friction
force developed by two surfaces, when one surface tends to prevent motion across another surface
Point of application
Point to where the vector is applied to the object
Newton’s 1st law of motion (the law of inertia)
An object at rest tends to stay at rest
An object in motion tends to stay in motion
How does force apply to the law of inertia (1st newton law)?
force is needed to cause the object to overcome the inertia: move, stop, or change direction/ velocity
Force can be used to initiate movement or stop an object
Acceleration
is change in velocity and direction of an object
Newton’s 2nd law of motion (the law of acceleration)
Change in acceleration occurs depending on the amount of force or strength of the force
applied to the object.
Force is needed to change direction.
Acceleration is inversely proportional to mass.
If you apply the same amount of force to two objects of differing mass which object will accelerate more?
The object with greater mass/heavier will move less, as compared to the object with less mass.
Newton’s 3rd law of motion (the law of action- reaction)
For every action there is an equal and opposite reaction
Give examples of the Newton’s 3rd law of motion?
Jumping on a trampoline
Action= jumping down on trapoline
Reaction= trampoline pushing back up with the same amount of force
The harder you jump the higher you rebound
Linear force
two or more forces acting along the same line in the same direction
Parallel forces
Vector that moves in the same or opposite direction in the same plane. (Three forces-3 point bracing: two forces are applied in the same direction (concurrent force) while a middle force counters the two opposing forces.
Concurrent force
Two or more vector quantities that act upon a common point that pulls or pushes in different directions- can produce a Resultant Force.
Force couples
two or more vector quantities that pull or push in different directions resulting in rotation
What force couple produces scapular rotation
Trapezius (upper & lower fibers) and Serratus anterior
Upper trap pulls up, lower trap pulls down, & serratus anterior pulls out allowing for scapular rotation
Using a wrench, what can be done to increase the amount of torque?
increasing the force applied to the handle or increasing the length of the handle
What is the perpendicular distance from the force’s line of pull to the axis of rotation
moment arm
When is torque greatest?
When the angle of pull is at 90 degrees
When would no torque be produced?
if the force is directed exactly through the axis of rotation
ie- if the biceps contracts when the elbow is nearly or completely extended there is very little torque produced
Occur b/c perpendicular dist. b/t the joint axis & line of pull is very small
What is a stabilizing force
Angle of pull less than 90 degrees
when all the force generated by a muscle is directed back into the joint, pulling the two bones together
When is the angle of pull at its largest?
at 90 degrees
What occurs when angle of pull is at 45 degrees?
Rotary & stabilizing forces are equal
In regards to the moment arm & stabilizing force what occurs when the joint moves towards 0 degrees (elbow extension)?
Moment arm decrease
stabilizing force increases
In regards to the moment arm & dislocating force, what occurs when the joint moves beyond 90 degrees toward 180 degrees (elbow flexion)?
Moment arm decreases
Dislocation force increases
In regards to the moment arm & angular force, what occurs when the joint is at 90 degrees of (elbow flexion)?
Moment arm and angular force are greatest in this position
What determines how effective a muscle is in causing joint motion?
Moment arm, size of the muscle, and contractile strength
An ______ in angular force causes _____ stabilization of the joints
Increase
less
The coracobrachialis has a ______ stabilizing force than angular force throughout the range. Making it more effective at _______ the joint than _____ it.
greater
stabilizing
moving
How does the patella affect torque produced by the quadriceps muscle.
The patella holds the quadriceps tendon out and away from the femur increasing the angle of pull creating a greater angular force
When is a joint most efficient at moving or rolling?
When it is near or at 90 degrees
This is why MMT is performed at midrange
What is a dislocating force?
increase angular force / increase distance causes the muscle to direct the force away from the joint; causes the joints to pull apart
Summary of Forces
A muscle is most efficient at moving, or rotating a joint when the joint is near or at 90 degrees.
The joint is near 180 degrees/0 degrees, then moment arm is small and can become a stabilizing force. When the angle becomes greater than 90 degrees, the angle becomes a dislocating force (angle reaches greater than 90 degrees).
Less force is required if you put the resistance as close to the axis as possible, and apply the force as far from the axis as possible
What is a stable equilibrium?
All forces acting on an object or joint evenly, causing stability
ie- think of when the widest part of a brick is in contact w/ the surface, it is quite stable
To disturb it the brick would have to be tipped up in any direction, raising it’s COG
What is an unstable equilibrium?
occurs when only a slight force is needed to disturb an object
ie- balancing a pencil on its pointed end or a person balancing on 1 leg
What is center of gravity (COG)
Planes in the body are all equal;
Balance point of an object where all torques forces are equal.
*higher in children than adults
Describe neutral equilibrium?
when an object’s COG is neither raised nor lowered when it is disturbed
ie- a ball rolling across the floor maintains same COG or person moving in a wheelchair
What is the line of gravity (LOG)?
Imaginary line through the COG and the BOS
Lever
is rigid and can rotate around a fixed point when a force is applied
Axis
the point around which a lever rotates
Resistance
the EFFORT that causes the lever to move
Describe a first class lever?
The axis is located b/t the force & resistance
F_________R
A
What is the force arm (FA)?
the distance b/t the force and the axis
What is the resistance arm (RA)?
The distance b/t the resistance and the axis
If the axis is close to the resistance?
RA will be shorter
FA will be longer
Resistance will be easier to move
If the axis is close to the force?
RA will be longer
FA will be short
Resistance will be harder to move
What is an example of a first class lever in the human body?
Head sitting on 1st cervical vertebra moving into flexion & extension
Describe a 2nd class lever?
the resistance is in the middle w/ axis on one end and force at the other
A____R____F
What is an example of a second class lever?
A loaded wheel barrow Standing on your tip toes Foot= Axis Resistance = Bodyweight Force= Plantar flexors
Second class levers favor?
Force
Third class levers favor?
Distance
Describe a third class lever?
the force is in b/t the resistance and the axis
A____F_____R
Demonstrate a third class lever in the body
Elbow flexion
Biceps brachii attaches b/t the axis (elbow) and the resistance weight of forearm
How can you change from a second class lever to a third class lever?
During elbow flexion/extension, the concentric portion acts as a 3rd class lever, the eccentric portion acts as a 2nd class lever
How can you change the brachioradialis from a 2nd class lever to a 3rd class lever?
2nd class elbow A, forearm R, brachioradialis attaching to styloid process of radius F By adding a weight to the hand the R is now further than the F. A is the elbow, F is brachioradialis, R is the weight in the hand
What uses less energy when holding a box?
Holding the box closer to your body
Summary of mechanical advantage
Less force is required if you put the resistance as close to the axis as possible and apply the force as far from the axis as possible
This concept is applied during manual muscle testing, MMT
What is the purpose of a fixed pulley?
To change the magnitude or the direction of force
A pulley acts as what type of lever?
Acts like a first class lever-one side of the pulley has force with a middle axis and the other side has the resistance
What muscle in the body acts like a pulley?
Lateral malleolus of the fibula acts as a pulley for the Peroneus longus tendon
What is the purpose of the wheel & axle?
Used to increase force exerted on an object
Larger the wheel easier to turn the object- less force is required to turn the wheel
Smaller the wheel harder to turn the object-more force is required to turn the wheel
