Exam 1: Biomechanics Concepts

the rolling or rotation at a joint around a center of rotation (angular motion)

y-direction, up, and to the right

the glide or translation at a joint (linear motion)

x-direction, down, and to the left

a single point rotates like a top spinning

axis of a joint shifts in space as it moves

plane: x-y plane dividing the body into front and back

axis: z (anterior/posterior)

motion: abduction/adduction/lat flexion of the trunk

plane: y-z plane dividing the body into left and right

axis: x (medial/lateral)

motion: flexion/extension + dorsiflexion/plantarflexion

plane: x-z plane dividing the body into top and bottom

axis: y (superior/inferior or longitudinal/vertical)

motion: rotations

number of planes a joint can move in

distal segment is fixed to the earth or immovable surface while the proximal segment is free to move

stand to sit, stance phase of gait (and with a cane planted)

distal segment is free to move in space

hand to mouth, sitting knee extension, swing phase of gait

convex moving on stable concave: roll and glide occur in opposite directions

concave moving on stable convex: roll and glide occur in the same direction

locked position of a joint

1. joint surfaces are maximally congruent

2. ligaments and capsule are taut and twisted

3. usually at end range

any unlocked position at a joint where the ligaments and capsule are lax

ROM in degrees

distance in cm

F (N) = m(kg) x a(m/s²)

unloaded

tension

compressions

bending

shear

torsion

combined loading

change in length occurs

take up slack

point B

elongation is linear, return to beginning (no change)

point B-C

progressive failure of tissue; permanently deformed

point C-D

when plastic region begins

point C

fracture, break, or tear occurs

point D

energy is lost as heat when tissue deforms and change in length is permanent

point C-D

when a tissue is stretched, the tissue elongates and the diameter decreases

decreased diameter leads to increased stress

repetitive loading weakens materials

faster is more likely to fx so slower leads to creep

muscles, ligaments, and bones

gravity and equipment

have a base, magnitude, and direction

all muscles are these

up, right, or counterclockwise direction

down, left, and clockwise direction

begins on the bone @ the point of insertion and goes in the direction of the muscle pull

starts at the insertion and is always perpendicular to the bone it inserts on

starts at the insertion and runs parallel to the bone it inserts on

hypothetical point at which all mass would appear to be concentrated and where the force of gravity will act → point of balance

anterior S2

a line drawn from COG directly down to the surface

always equal/opposite in magnitude to the gravity reaction force

feet and the space between (a box drawn around them)

adding an assistive device will increase the BOS

height of the COG above BOS, size of BOS, location of LOG within BOS (bending over), and COG of the body

squatting: LOG stays centered

bending over: LOG shifts anteriorly and decreases stability since there is extra translation

linear, concurrent, and parallel

force couples and levers

when 2+ forced act on the same object in the same line (joint compression and distraction)

tensile forces (often gravity)

joint reaction forces (often mm or surface contact)

2+ forces acting at a common point of application, but in divergent directions

composition is through a parallelogram

2+ forces act on the same object but at some distance from each other and never converging

i.e. bones

2 forces are equal in magnitude and opposite in direction; always produces rotation

three forces of a mechanical level and has three components: A, R, E

A = axis

R = resistance (loser)

E - effort (winner) and acting in the direction of rotation

= EA/RA

EAR or RAE

EA < = > RA

ERA and ARE (most efficient)

EA always > RA

AER and REA (least efficient)

EA always < RA

occiput on C1

it depends

bicep curl

> 1.0

< 1.0

the ability of a force to cause rotation of a lever

T = f x d

shortest distance between the action line and the joint axis

greatest when force is at 90 degrees to the segment

drawn perpendicular to the action line and intersects the joint axis

change the direction of pull without changing the magnitude of the force

i.e. sesamoid (patella) bone

connective tissue binds joints

fibrous and cartilagenous

fibrous tissue connects bone to bone

i.e. skull sutures, gomphosis, and tibia+fibula

joined by fibro or hyaline cartilage

i.e. pubis symphesis, growth plates, ribs to sternum)

ends of bones are free to move + joint capsule

jt. receptors in fibrous outer layer attache to the periosteum with Sharpey’s fibers

nerve supply is disrupted which decreases proprioception

joint capsule, joint cavity, synovial membrane, synovial fluid, and hyaline cartilage

provides nourishment, removes waste, and lubricates by diffusion via movement

decreases friction and absorbs shock

uniaxial, biaxial, and triaxial

1 DOF

hinge and pivot joints

inter-phalangeal and atlas-axis

2 DOF

condyloid and saddle joint

metacarpal-phalangeal and carpal-metacarpal of thumb

3 DOF

plane and ball-and-socket

carpal bones and hip/shoulder

cellular matrix and extracellular matrix

fibroblasts mature into fibrocytes, chondrocytes, tenocytes, or blastocytes

ground substance and fibrous proteins

GAGS (+) affect hydration and contribute to the strength of collagen to withstand compression

keeps extracellular matrix together with collagen and elastin

accounts for 30% of all protein in body and has tensile strength

type I or II

thick and stiff

thin

elastic and deforms under force and returns back to original state

tells us the strength and stiffness of the tissue

dense, articular cartilage, and fibrocartilage

ligaments, joint capsule, and tendons