lecture 1, exam 1 study guide Flashcards
contrast the fundamental difference between kinematics and kinetics
kinematics - motion of a body without regard to the forces or torque that may have produced the motion
kinetics - forces (or torques) that act on or within a body.
what is an example of kinematics?
walking velocity and angular displacement (ROM) of a joint
what is an example of kinetics?
compression of an articular disc or tension within a stretched ligament
describe a particular movement of the body or body segment that incorporates both translation and rotation kinematics
the arthrokinematics of glenohumeral abduction include a roll (rotation) and a slide (translation)
give another example of an action that includes both translation and rotation
walking includes a linear displacement (translation) of the center of mass of the body as a whole, as well as a concurrent rotation of the joints within the limbs
which position of the MCP joint has greater accessory movements?
passive accessory motions at the metacarpophalangeal joint are greater in or near full extension
which position would you assume is the MCP joints closed packed position?
the close packed (and most stable) position of this joint is therefore in near full flexion.
at the MCP joint, the close packed position is associated with elongation and increased tension in the joint’s collateral ligaments
what is a force?
a push or pull applied against a mass
use force to describe a particular aspect of a muscle’s contraction relative to a joint
a contraction force produced by the elbow flexor muscles can create significant compression within the elbow joint
what is torque?
rotary equivalent of a force, with its magnitude equal to the product of a muscle force and its moment arm
use torque to describe a particular aspect of a muscle’s contraction relative to a joint
the torque produced by the elbow flexor muscles can produce rapid angular acceleration of the elbow, quickly bringing the hand to the mouth
what is internal torque and what is an example of it?
torque produced around a joint driven by an internal force
example: muscle contraction
what is external torque and what’s an example of it?
torque produced around a joint caused by an external force
example: gravity or manual resistance applied by a therapist
what happens when opposing internal and external torques about a joint are equal?
the joint is in static rotary equilibrium
what happens if the internal and external torques are not equal?
the joint would accelerate in the direction of the larger torque
how is the type of muscle activation affected when you slowly lower a book to the table?
slowly lowering a book to the table occurs through an interaction of gravity acting on the book and eccentric activation “braking” of the elbow flexor muscles
the elbow flexor muscles control the movement by decelerating the descent of the book
how is the type of muscle activation affected when you rapidly lower a book to the table?
to accelerate the book toward the table at a rate that exceeds the pull of gravity, the elbow extensor muscles must contract via concentric activation to produce the rapid descent of the book
describe a possible pathologic situation in which the inferior-directed joint reaction force is not able to be generated by the distal humerus
a large inferior-directed joint reaction force is normally required to match the large internal (elbow flexor) force. a humerus severely weakened by osteoporosis may fracture in response to the strong pull of the muscle. In this case, the structure of the humerus is unable to generate an adequate reaction force allowing the forearm to accelerate upward through the fractured distal humerus. This pathologic situation tends to occur with greater frequency in joints that are subjected to very large forces, such as the hip
in the context of a patient with a spinal cord injury and reduced sensation, how would you protect their skin from force and pressure?
force = magnitude of a push applied against the patients skin
pressure = force divided by the contact area
in a person with a spinal cord injury, they often have impaired sensation and not able to perceive damaging level of contact pressure. if a force is applied to a small surface area it can cause damaging pressure (stress). high contact pressure can lead to ulceration of skin and tissues.
to reduce pressure, you must maximize the contact area between skin and external object, like a seat of a wheelchair. ideally, use a fitted wheelchair with proper seat cushion to maximize surface area that contacts the ischial region.
True or false. Even a wrinkle in clothing can create potentially damaging high pressure against insensitive skin
true
true or false. weight = mass.
if false, describe the difference.
false
mass describes the number of particles that exists in an object.
weight is force that describes the gravitational pull exerted on a mass.
how do you find a person’s mass?
divide the person’s body weight (N) by the acceleration caused by gravity (9.81 m/sec2)
what is degrees of freedom?
the number of independent directions of movements allowed at a joint or the number of permitted planes of angular motion
how many degrees of freedom in the shoulder? wrist? elbow?
shoulder = 3
wrist = 2
elbow = 1
