The Basics Flashcards
Objectives
- Define Torque and differentiate types of torque
- Discuss the joint forces created by various types of lever systems and torques created during human movement
fyi
For a PTA, the purpose of studying clinical kinesiology (how the body moves) is to understand the forces acting on the human body causing movement (biomechanics) and to manipulate these forces in treatment procedures so that human performance may be improved and further injury may be prevented
Clinical Kinesiology
built on the study of mechanics from the field of physics.
it is the study of how forces lead to movement in the human body.
Biomechanics
what is concerned with the effects of forces acting on objects.
Mechanics
Humans can see movement but forces affecting motion are never seen and seldom felt. What are 4 main forces on the body:
- Gravity
- Muscle tension
- External resistance
- Friction
Where these forces act in relation to positions and movement of the body in space is fundamental to the ability to produce human movement and to modify it
weight of body parts and attachments such as splints, casts, eating utensils, books or weights
Gravity
produce forces on the bone segments by active contraction or by being passively stretched
Muscles
exercise pulleys, manual resistance, doors or windows
Externally applied resistances
can provide stability if optimum, retard motion if excessive and lead to instability if inadequate
Friction
deals with NON-movement systems
Statics
deals with moving systems and can be divided into two parts:
Dynamics
forces causing movement in a system
Kinetics
the science of motion of bodies in space, osteokinematics and arthrokinematics
Kinematics
how the bones move in space without regard to the movement of joint surfaces
Osteokinematics
how adjoining joint surfaces move in relation to each other
Arthrokinematics
a quantity having both magnitude (size) and direction
Vector
Force is a
vector
a push or a pull action that can be represented as a vector
Force
describes only magnitude
Length, area, speed, volume and mass
Scalar
refers to the amount of matter that a body contains
Mass
the property of matter that causes it to resist an change of its motion in either speed or direction
Inertia
a description of motion with regard to what causes motion
Kinetics
the tendency of force to produce rotation about an axis
Torque
a force developed by two surfaces
Prevents motion of one surface across another
Friction
a vector that describes speed and is measured in units
Feet per second
Miles per hour
Velocity
NO motion can occur without a force
what are some internal forces?
muscular contraction, ligamentous restraint, tendon restraint, bony support
NO motion can occur without a force
what are some external forces?
gravity, weight, friction, etc.
Push vs Pull
- Push creates compression
- Pull creates tension
- Movement occurs when one side of force is greater than the other (tug of war)
Forces are vector quantities. A vector quantity describes both ?
magnitude and direction
results when two or more forces are acting along the same line
Linear force
occurs in the same plane and in the same or opposite direction
Parallel force
two or more forces must act from a common point but pull in different directions
Concurrent force
The net effect of these two concurrent forces is called the __________ force and lies somewhere in between
resultant
known as the moment of force
The ability of force to produce rotation about an axis
Rotary force
Torque
The amount of torque on a lever depends on-
- the amount of force that is applied
- and the distance it is from the axis
Torque (in the body) is the amount of force needed by a _________________ to cause_______________.
- muscle contraction
- rotary joint action
“the torque arm” - is the perpendicular distance between the muscles line of pull and center of the joint (axis of rotation)
Moment arm
Torque is greatest when the angle of pull is at___ degrees and decreases as the angle of pull either decreases or increases from the perpendicular position
90
When nearly all of the force generated by the muscle is directed back into the joint, pulling the bones together.
Stabilizing force
This occurs in joints when they are close to 0 degrees. They have a small moment arm, therefore the force is directed at stabilizing the joint and not at producing angular movement or torque.
Stabilizing force
Most of the force generated by the muscle is directed at moving the joint and not _______ the joint
stabilizing
As a muscle contracts, the amount of angular force or stabilizing force changes how?
Angular force increases, stabilization force decreases
Past 90 degrees, the stabilizing force becomes a ___________force because the force is directed away from the joint
dislocating
Angular Force (Torque)
When the angle of pull is at 90 degrees, the perpendicular distance between the joint axis and line of pull is much larger
When an object is balanced and all torques acting on the object are even, the object is in a
State of Equilibrium
How stable is the State of Equilibrium?
Depends primarily on the relationship between the object’s center of gravity and base of support
the mutual attraction between the earth and an object
Gravity
always directed vertically downward toward the center of the earth
Gravitational force
the balance point of an object at which torque on all sides is equal
Center of gravity – COG
the part of the body that is in contact with the supporting surface
Base of Support (BOS)
an imaginary vertical line passing through the COG toward the center of the earth (pg. 100)
Line of Gravity (LOG)
The degree of stability (resistance to being overthrown) of a body depends on four factors:
- The height of the center of gravity above the base of support
- The size of the base of support
- The location of the gravity line within the base of support
- The weight of the body
Stability is enhanced by
- Low center of gravity
- Wide BOS
- Gravity line at center of support
- Heavy weight
Instability is enhanced by
- High COG
- Narrow BOS
- Light weight
occurs when an object is in a position that to disturb it would require its COG to be raised
Stable equilibrium
occurs when only a slight force is needed to disturb the object
Unstable equilibrium
occurs when an object’s COG is neither raised nor lowered when it is disturbed
Neutral equilibrium
Rules for COG
- The lower the COG, the more stable the object
Shorter people vs Tall people
- The COG and LOG must remain within the BOS for an object to remain stable
- The wider the BOS, the more stable the object
- When the COG is no longer over the BOS, the object will fall
- Stability increases as the BOS is widened in the direction of the force
Person vs Wind
- The greater the mass of the object, the greater the stability
- The greater the friction between the
- supporting surface and BOS, the more stable the body will be
Ice vs carpeting
- People have better balance while moving if they focus on a stationary object, not a moving object
Using adaptive equipment
- Playground seesaw, force is pushing up, the weight of the other child is the resistance
- If the distance is not equal between the force and resistance, more effort is needed to make the lever work.
First class levers – FAR – F=force (effort), A=axis (fulcrum), R=resistance (load)
Frequently used for maintaining postures or balance
Examples:
- Atlanto-occipital joint – the head is balanced by neck extensor muscle force
- Intervertebral joints in sitting or standing where the weight of the trunk is balanced by the erector spinae muscle forces acting on the vertebral axis
First Class Levers
Wheelbarrow – the wheel at the front is the axis, the contents is the resistance and the person pushing the wheelbarrow is the force
Second class lever – ARF – A=axis (fulcrum), R=resistance (load), F=force (effort).
Provide a force advantage such that large weights can be supported or moved by a smaller force
Examples:
- Limited examples in the body
- The only muscle example is the pull of the plantar flexors and the brachioradialis and the wrist extensors to maintain the position of elbow flexion
- This brachioradialis changes to a 3rd class lever when a weight is placed in the hand
Second Class Levers
- The most common lever in the body
- The resistance arm is always longer than the force arm (requires more force but moves a larger distance) and the mechanical advantage may be 0.1 or lower
- All three levers demonstrate that what is gained in distance is lost in force and conversely what is gained in force is lost in distance
- Third class levers typically favor distance while second class levers favor force (8-29)
Third Class Levers
- The brachioradialis is typically a 2nd class lever but if you put a weight in your hand, the resistance from the weight acting with gravity changes it to a 3rd class lever
- The weight of the object (5 pounds vs 100 pounds) will typically not change the class of the lever
Weight changes (8-30) Factors that can change class
Concentric vs eccentric movement - regarding the biceps and extension. If you place a weight in the hand and extend the elbow, your biceps is now a 2nd class lever
Factors that can change class Direction of movement (8-31)
The ratio between the force arm and the resistance arm
Mechanical Advantage
The mechanical advantage (MA) of a lever is determined by?
dividing the length of the force arm by the length of a resistance arm
MA = FA / RA
If the force arm is 2 feet and the resistance arm is 1 foot, the MA would be 2
If the force arm is 1 foot and the resistance arm is 2 feet, the MA would be ½ and therefore it would have half of the torque or rotary force
MA = FA / RA
If the force arm is 2 feet and the resistance arm is 1 foot, the MA would be?
2
MA = FA / RA
If the force arm is 1 foot and the resistance arm is 2 feet, the MA would be?
½
and therefore it would have half of the torque or rotary force
Simple machines/levers – what is gained in force is lost in __________ and vice versa
distance
To move an object using less force (MA>1) will also require that force arm to move a greater distance.
In other words, if we want to use less force we have to?
go farther to produce torque.
To move an object using more force (MA<1) will require that force arm to move a lesser distance.
If we use more force, we don’t have to what?
go as far to produce torque.
If the MA = 1, the system would be balanced as in a?
class 1 lever
fyi
Less force is needed when the mechanical advantage is greater
fyi
In 2nd and 3rd class levers, you want to move the ________of weight closest to the _______ so the resistance arm is shorter
load ,axis
FYI-Distractive Components of Weights
Weights applied to the extremities frequently exert traction on joint structures which may or may not be therapeutically desirable
fyi
Consists of a grooved wheel that turns on an axle with a rope or cable riding in the groove
- Goal – change direction of a force or to increase or decrease the magnitude of a force
Pulleys
a simple pulley attached to a beam/weight
- Does not provide any mechanical advantage to the force, but only changes the direction
Fixed pulley
one end of the rope attached to a beam and the rope runs through the pulley to the other end where the force is applied
- The load is suspended from a moveable pulley and is supported equally by both segments on either side
- Half of the force is needed to lift, but the rope has to be pulled twice the distance
- Mechanical advantage of the force is 2
Moveable pulley
Several structures in the human body are called pulleys because they have properties of a_______pulley
single
A pulley may provide a mechanical advantage to the muscle by lifting the tendon away from the????
- Quadriceps and the patellar tendons
- Not only change the direction of pull as the knee flexes but improves the force arm distance because of the position of the patella
joint axis
Less common, but a simple machine found in the body (8-36)
- Typically used to increase the force exerted
- Large radius (wheel) requires less force and a small radius requires more force to move
Mechanical advantage, MA = radius of the wheel/radius of the axle
The larger the mechanical advantage, the easier it is to turn the handle bu_t again_ the farther the handle needs to be turned
Wheels and Axles
- A flat surface that slants or a ramp (8-39)
- The longer the distance of the ramp, the less effort it takes to execute the task
- The shorter the distance of the ramp, the more effort it takes to execute the task
Inclined Plane
