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64 Cards in this Set

  • Front
  • Back
What type of motion?

The number of independent movements allowed at a joint.

A joint can have up to three degrees of translatorymotions and three degrees of rotatorymotion.
degrees of freedom

Describes the motion that occurs between the articular surfaces of the joints.

Three movements: roll, slide, & spin
For a convex-on-concave surface movement, the convex member rolls and slides in opposite direction
ArthrokinematicPrinciples of Movement

External Factors

Friction, air resistance, water resistance

Anatomic Factors:(modify motion of body segments)

Friction in joints

Tension of muscles, ligaments & fasciae

Anomalies of bones & joint structure

Presence of interfering soft tissue (fat)
Factors that Modify Motion:
types of motion
Linear motionis the movement of all body parts in the same direction and at the same velocity.

Angular motionprovides for the circular rotation of an object around an axis,

Curvilinear motionis the movement of an object along a curved but not circular path
Joint Motionis described in degrees of freedom of independent movement.

Jointsmove by rolling, sliding, spinning, and any combination of these motions.
joint movement
Push & pull exerted by one object on another that can produce, arrest, or modify movement.
Two consequences of force
A force acting on a body has two effects, one to move it and two to rotate it.
Normal forces that push 2 surfaces together
comprehensive forces
Streching force

Normal forces that push 2 surfaces together
tensile force
What type of force?
What type of force?
tensile forces
What type of force?
Normal forces that act parallel to the surfaces

a stress which is applied parallel or tangential to a face of a material, as opposed to a normal stress which is applied perpendicularly.

Opposite directions
Principal types of force acting to move or stabilize the musculoskeletal system can be:

Internal forces: produced from structures within the body

External forces: produced from structures outside the body
What type of force?

Active: generated by muscles

Passive: generated by tension

Internal Force
what type of force?

Gravity pulling on body mass

External load, such as weights

Physical contact
types of external force
To describe force, you must know:
To describe force, you must know:

Magnitude(spatial quality/extent of the force being exerted)

Direction(pull toward or away from the source)

Point of application(point at which the force is applied to an object)
a graphical representation of a force; straight line drawn to scale, with an arrow pointing the direction of the force
Vector –a graphical representation of a force; straight line drawn to scale, with an arrow pointing the direction of the force
2+ forces acting along the same line, in same or opposite direction
Linear Force
Force action lines are parallel, in the same plane, and act at different points; same or opposite direction

E.g., lever system or 3-point bracing system; 3rdforce between them = stabilizer (law of action-reaction)
parallel forces
Two forces of different magnitudes & opposite direction applied simultaneously to an object
Force Systems

2+ Forces acting at angles from a common point of application
Example of Force Couple in the Body
:Movement of the scapula

____is not a standard term in mechanics.

____is used to designate the ability to produce or resist a force.

Muscle______ maybe measured in terms of the ability to overcome a resistance, to resist forces, or to support a load.
is defined as the rate of doing work or work done per unit of time
= work / time
is defined as the product of force and displacement of object in direction of the force as the force is applied
= weight x distance x repetition
The human body moves because the musculoskeletal system is a system of _________
a rigid bar acted upon at two different points by opposing forces

They allow us to either do something with less effort or to increase the speed or force of an object being moved..
Lever Components
Lever Components

Fulcrum (axis) = A

Force Arm (force applied) = F

Resistance Arm (weight arm) = R
What type of lever?


Fulcrum is between the weight (R) and force (F) arms

Lever characteristics

balanced movement

axis is midway between force and resistance

e.g.: seesaw

speed and range of motion

axis is close to force

e.g.: elbow extension


axis is close to resistance
first class lever

This type of lever favors equilibrium.

This lever is used to gain either force or distance.

It is the most versatile of the three levers.

Frequently used for maintaining postures or balance.

Commonly used in orthotics, called a 3-point system for applying force.

Examples: seesaws, scissors, crowbars, & jacks
first class lever
What type of lever?
first class lever
What type of lever?

Weight (R) is between the fulcrum and force (F) arm
second class
What type of lever?
second class
lever provides a force advantage to support large weights or to be moved by a smaller force.

This type of lever favors the force of effort.

Force arm is always greater (longer) than the resistance arm.

ROM is sacrificed to gain force.

In the human body, this type of lever is seen when gravity is the force and muscles are the resistance.

E.g. wheelbarrow,Nutcracker,Paddle,
Second Class Lever
What type of lever?

Force (F) arm is between the fulcrum and weight (R) arm
lever used to produce speed & distance of the distal segment of the body

What is gained in speed or distance is lost in force.

What is gained in force is lost in speed.

Force arm (FA) will always be shorter than the resistance arm (RA)

Designed to produce speed and distance of movement at the expense of force; allows minimal muscle shortening because the muscles insert near the joint

Most common lever type in the body.

Ex. Baseball bat, Boat paddle, Broom, Electric Gates, Fishing rod, Hockey stick, Mandible, Mousetrap (Spring-loaded bar type), Shovel (the action of picking or lifting up sand or dirt), Stapler, Tongs, Tweezers, Hammer, Tennis racket, The Human Arm
third class lever
rigid bar which moves around a fulcrum (axis) for motion
in a leverage system when does movement occur
Movement occurs when the force of muscle contraction is sufficient to overcome the resistance, which is at least the weight of the part being moved
first class lever
second class lever
third class lever
What type of Lever?
First Class Lever
What type of lever?
2nd class
What type of lever?
third class
The principles of the ______are used to visualize the complex system of forces that produce rotary motion in the body –muscles, gravity, & physical contact.
A lever is in balance or______ , when force x force arm = resistance x resistance arm

Refers to the efficiency of a lever.

Is the relationship between the length of the force arm (FA) and the length of the weight arm (RA)
MA = FA / RA

When only a small effort of force is needed to overcome a larger resistance, the lever is efficient.
mechanical advantage
: waste energy and force to gain speed and distance
3rdClass Levers
utilizes less force and energy to gain little speed or distance.
2ndClass Levers:
Majority of the human body levers are quite ________as far as force requirements are concerned, but they do provide a large amount of motion at the distal end.

Goal of human function is the placement or relocation of the distal segments of the body.
the most constant force encountered by the body. It affects the stability of the body as well as the movement of the trunk, extremities & head.
is enhanced by a low center of gravity, wide base of support, the gravity line at the center of the support, & heavy weight.
Any change in _____distribution results in a change in the center as well as line of gravity.

is enhanced by a high center of gravity, narrow base of support, & light weight.
--------can & does provide the force for motion.
are easier to maintain when the base of support is increased or the center of gravity is lowered.
Balance & Stability

Used to gain force, distance, or stability
The human body uses a system of _______to move. The -------of a muscle pull directly effects the force it is capable of producing.

Allows for support of large weights or for the weights to be moved by a smaller force

Utilizes less force and energy to gain little speed or distance.

Produces speed & distance of distal segment

Wastes energy & force to gain speed & distance
Changing the length of the force arm (FA) or resistance arm (RA) will make

Movement easier or harder and

Lever more or less efficient.