KHS 325 - TEST 1 (MIDTERM)

only contains topics I need to review

major joint motions for sagittal plane

• flexion/extension: head, trunk, upper arm, forearm, thigh, knee, palms, feet

• hyperextension

major joint motions for frontal plane

• abduction/adduction

• lateral flexion: trunk and head

• elevation/depression: scapula

• radial/ulnar deviation: wrist

• inversion/eversion: sole of foot

major joint motions for transverse plane

• medial/lateral rotation: twisting limb “inside” or “outside”

• left/right rotation: head, neck, trunk

• pronation/supination: forearm

• horizontal adduction/abduction: moving horizontal arms from sides to front

linear motion

all points on body show same trajectory; orientation of object does not change

rectlinear — straight path (ice skating)

curvilinear — curved path (skiing down hill)

angular motion

rotation about an axis of rotation; orientation changes constantly

axis of rotation can be within body (lifting legs while lying down) or outside (trapeeze)

general motion

combination of linear and angular motion

linear motion of center of mass (CM), angular motion of object about its CM

ex: kicking ball toward goal

center of mass

point around which all mass of a body is balanced in all directions

force

push or pull acting on a body that causes motion

symbol: F

standard unit: N

why is force important in biomechanics?

key quantity of interest in kinetics

ex: muscle forces, weight (gravity), friction

3 important properties of force

direction

magnitude

point of application

pressure

amount of force acting over a unit area

P = force / contact area

standard unit: Pa (aka N/m²)

torque

rotary force that produces angular motion

T = F * moment arm

standard unit: Nm

vector quantity (uses - and +)

why is mechanical loading important?

1. to prevent injury or damage, body needs to absorb energy from internal and external forces

2. advantageous to absorb force over large areas to spread absorption rate

3. stronger and healthier tissues likely to withstand excessive loading

mechanical stress

disturbance of force inside a solid body

stress = force / cross-sectional area

mechanical strain

deformation due to stress

stiffness of tissue affects mechanical strain

stiffer = less deformation

load-deformation curve (stress-strain curve)

as load increases, deformation increases until it hits the yield point

yield point = permanent deformation

failure point = loss of mechanical continuity

if slope is steeper, the body is stiffer (smaller elastic region)

compression

pressing/squeezing force directed axially through a body

tension

pulling/stretching force directed axially through a body

shear

force directed parallel to a surface

bending

asymmetric loading (tension on one side, compression from the other)

torsion

twisting of a body around longitudinal axis

acute vs repetitive loading

acute — application of single force of sufficient magnitude causes injury

repetitive — repeated application of subacute load usually of low magnitude

components of a machine system

movers/motors — produces forces

machine body — changes magnitudes and directions of forces

resistor — provides resistance

examples of human machine system

moves/motors = heart and skeletal muscles

machine body = bones and joints

resistor = body itself or environment

sources of human mobility

muscle torque

causes joint motions

moment arm of muscle

distance from joint center to muscle’s line of action

varies as joint angle changes

max when angle of pull is 90 degrees

lever and its elements

simple machine with bar-like body that rotates about an axis

1st = raising chin to look up (atlanto-occipital joint)

2nd = tiptoeing (most levers used in daily life bc MA)

3rd = lifting an object (majority of human body joints)

mechanical adv

gain of the system = output / input

mechanical function of skeletal system

provides rigid skeletal framework (support and protection)

forms rigid levers (can be moved by muscle force)

3 main material constituents of bone and their properties

minerals = 60-70%

• stiffness and compressive strength

water = 25-30%

• flexibility and tensile strength

collagen = 10%

• contributor to bone strength

type-bone combinations

short bones

long bones

flat bones

irregular bones

sesomoid bones

typical structure of long bone

epiphysis

• articular cartilage

• epiphyseal plate

• trabecular (spongy) bone

diaphysis

• cortical (hard) bone

• marrow (medullary) cavity

• periosteum and endosteum

• nutrient artery

how are joints classified?

either by function or structure

• synarthroses — fibrous joints; immovable

  • skull sutures, mid-radioulnar, midtibiofibular

• amphiarthroses — cartilaginous joints; slightly moveable

  • 1st sternocostal, epiphyseal plate, vertebrae, pubic symphysis

• diarthroses — synovial joints; freely moveable

  • major joints of body

gliding/plane joint

surfaces of bone slide over each other; flexion and extension through slight gliding motion

0 axis; 1 DOF

ex: intermetatasral, intercarpal, intertarsal, facet joints (vertebrae)

hinge joint

joining 2 bone ends with smooth surfaces (ML axis); extensive flexion and extension with small amount of rotation

1 DOF

ex: humeroulnar (elbow)

pivot joint

allows turning; rotate around 1 axis (L axis)

1 DOF

ex: proximal and distal radioulnar joint, atlanto-axial joint

condyloid joint

ovular convex of one bone end fits into full concave shape of adjoining bone; movement in all directions

2 DOF

ex’: radiocarpal joint

saddle joint

when concave and convex surfaces meet; allow movement of joint forward and backwards and left and right

2 DOF

ex: carpometacarpal of thumb

ball-and-socket joint

one end of bone shaped like ball fits into hollow socket at end of another joint; greatest range of motion; held by ligaments and tendons

3 DOF

ex: acetabulofemoral joint, glenohumoral joint

joint stability

ability to resist dislocation

prevents injuries to surrounding ligaments, muscles, and tendons

high stability desired —> increase via strength

factors affecting joint stability

shape of bone structure (depth vs shallowness)

ligaments arrangement

fascia (thin vs tough + fibrous membranes)

joint flexibility

ROMs allowed at joint; joint specific

increase via stretching

factors affective joint flexibility

shapes of articulating bone surfaces

intervening muscles or fatty tissues

laxity

extensibility of collagenous tissues and muscles

fluid contents in cartilaginous disc

temperature of collagenous tissues (warm-up)

shoulder vs hip stability

hip has higher contact area = more stability

special structures that improve knee joint stability

menisci

ACL and PCL

ML collateral ligaments

mechanical functions of skeleton muscles

develops tension

moves limbs: 75 muscle pairs out of 434 muscles

maintain upright posture

absorb shock

40-50% body weight

concentric contraction

length decreases

force > resistance

eccentric contraction

length increases

force < resistance

isometric contraction

length does not change

force = resistance

agonist

responsible for joint motion (primary and assistanct)

antagonist

acts against agonist for fine control and balance

stabilizer

stabilizes portion of body against particular force

neutralizer

prevents unwanted accessory actions that normally occur when agonist develops concentric tension

motor unit

single motor neuron + skeletal muscle fibers innervated

functional unit of muscle

all muscle fibers in one unit are the same fiber type

size principle

determines sequence of recruitment of motor units

smallest recruited first

SO —> FOB —> FG

fatigued —> recruit new motor units

what is force-length relationship (tension-length)

isometric characteristic

force generation is at peak when muscle is slightly stretched (just over resting length)

what is force-velocity relationship?

dynamic characteristic for concentric contraction

only holds true for max activated muscles

as load increases, velocity increases (slower action) for concentric… if it crosses isometric maximum, the muscle will start eccentric contraction

• isometric max — max force muscle can produce while static (not changing length)

muscular strength

ability of muscle or muscle group to exert max force against resistance

muscular power

ability to generate max force in fastest time; ability to release max muscular force

P = F*V

muscular endurance

ability to exert submax force repeatedly over time

factors: force and speed of activity; SO fiber proportion

fatigue = muscle unable to respond to stimulus