lecture 1, exam 1 study guide

Question 1

contrast the fundamental difference between kinematics and kinetics

Answer 1

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.

Question 2

what is an example of kinematics?

Answer 2

walking velocity and angular displacement (ROM) of a joint

Question 3

what is an example of kinetics?

Answer 3

compression of an articular disc or tension within a stretched ligament

Question 4

describe a particular movement of the body or body segment that incorporates both translation and rotation kinematics

Answer 4

the arthrokinematics of glenohumeral abduction include a roll (rotation) and a slide (translation)

Question 5

give another example of an action that includes both translation and rotation

Answer 5

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

Question 6

which position of the MCP joint has greater accessory movements?

Answer 6

passive accessory motions at the metacarpophalangeal joint are greater in or near full extension

Question 7

which position would you assume is the MCP joints closed packed position?

Answer 7

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

Question 8

what is a force?

Answer 8

a push or pull applied against a mass

Question 9

use force to describe a particular aspect of a muscle’s contraction relative to a joint

Answer 9

a contraction force produced by the elbow flexor muscles can create significant compression within the elbow joint

Question 10

what is torque?

Answer 10

rotary equivalent of a force, with its magnitude equal to the product of a muscle force and its moment arm

Question 11

use torque to describe a particular aspect of a muscle’s contraction relative to a joint

Answer 11

the torque produced by the elbow flexor muscles can produce rapid angular acceleration of the elbow, quickly bringing the hand to the mouth

Question 12

what is internal torque and what is an example of it?

Answer 12

torque produced around a joint driven by an internal force

example: muscle contraction

Question 13

what is external torque and what’s an example of it?

Answer 13

torque produced around a joint caused by an external force

example: gravity or manual resistance applied by a therapist

Question 14

what happens when opposing internal and external torques about a joint are equal?

Answer 14

the joint is in static rotary equilibrium

Question 15

what happens if the internal and external torques are not equal?

Answer 15

the joint would accelerate in the direction of the larger torque

Question 16

how is the type of muscle activation affected when you slowly lower a book to the table?

Answer 16

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

Question 17

how is the type of muscle activation affected when you rapidly lower a book to the table?

Answer 17

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

Question 18

describe a possible pathologic situation in which the inferior-directed joint reaction force is not able to be generated by the distal humerus

Answer 18

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

Question 19

in the context of a patient with a spinal cord injury and reduced sensation, how would you protect their skin from force and pressure?

Answer 19

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.

Question 20

True or false. Even a wrinkle in clothing can create potentially damaging high pressure against insensitive skin

Answer 20

true

Question 21

true or false. weight = mass.

if false, describe the difference.

Answer 21

false

mass describes the number of particles that exists in an object.

weight is force that describes the gravitational pull exerted on a mass.

Question 22

how do you find a person’s mass?

Answer 22

divide the person’s body weight (N) by the acceleration caused by gravity (9.81 m/sec2)

Question 23

what is degrees of freedom?

Answer 23

the number of independent directions of movements allowed at a joint or the number of permitted planes of angular motion

Question 24

how many degrees of freedom in the shoulder? wrist? elbow?

Answer 24

shoulder = 3
wrist = 2
elbow = 1

Question 25

does degrees of freedom include translational movements?

Answer 25

yes

Question 26

what are accessory movements?

Answer 26

slight passive translations within joints

Question 27

what does abnormal translation within a joint impact?

Answer 27

the quality of active motion - potentially creating microtrauma intraarticularly