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Biomech- ch.4 Bone+ ch13 stability
bone anatomy, stability and balance
55
Biology
Undergraduate 2
01/26/2012

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Term
2 mechanical functions of bone
Definition
rigid skeletal framework- support and protect body tissue
-levers that can produce body movement (Lever: relatively ridged object, rotate about an axis by the application of force)
-vascular +nerve supplied
Term
Composition of bone (4)
Definition
Calcium carbonate and calcium phosphate (60-70%)
other minerals (f, mg, na)
collagen
water- 20-30% body weight= transport nutrients and transpt and stores mineral ions, contributes to bone strength
(these vary with age and health of the bone-demineralizes- and loss of collagen- inc porosity)
Term
what produces stiffness in bone
Definition
produced by calcium carbonate and calcium phosphate
Term
yield point
Definition
point where permanent deformation occurs- moves from elastic to plastic region (will not return to original shape when stress is removed)
Term
compressive strength
Definition
ability to resist pressing or squeezing force
-det by Ca carbonate and ca phosphate
Term
tensile strength
Definition
ability to resist pulling or stretching force
-collagen
Term
anisotropic
Definition
exhibiting diff mechanical properties in response to loads from different directions

-bone is strongest in resisting compression -weakest in shear
Term
cortical bone
Definition
compact mineralized CT with low porosity found in the shafts of long bones

-stiffer- greater stress but less strain
Term
epiphysis
Definition
growth center of a bone that produces new bone tissue- part of normal growth process until closes in early adolescence or adulthood
Term
fracture
Definition
disruption in the continuity of a bone
Term
impacted
Definition
pressed together by a compressive load
Term
lever
Definition
relatively rigid obj that may be made to rotate about an axis by the application of force
Term
osteoblasts
Definition
specialized bone cells that build new bone tissue
Term
osteoclasts
Definition
specialized bone cells that resorb bone tissue
Term
osteopenia
Definition
condition of reduced bone mineral density that predisposes the individual to fractures- bc decreased osteoid production aka bone material
Term
osteoporosis
Definition
disorder involving decreased bone mass and strength with one or more resulting fractures
Term
periosteum
Definition
double layered membrane covering bone- muscle tendons attach to outside layer and the internal layer is a site of osteoblast activity
Term
stiffness
Definition
ratio of stress to strain in a loaded material
(slope of stress-strain curve)--within the elastic region

-stress divided by the relative amount of change in structure shape
Term
strain
Definition
amount of deformation divided by the original length of the structure or by the original angular orientation of the structure
strain=change in length/original length
Term
stress fracture aka. fatigue fractures
Definition
fracture resulting from repeated loading of relatively low magnitude
Term
stress reaction
Definition
progressive bone pathology associated with repeated loading
-microdamage-osteoclast resorb damage tissue, osteoblasts deposit new bone, if not enough time to repair=stress fracture
Term
trabecular bone
Definition
less compact mineralized CT with high porosity that is found in the ends of long bones and in the vertebrae

-more porous= smaller proportion of CaPO4 and CaCO3
-withstand greater strain less stress
Term
Bone anatomy
Definition
functional unit= osteon/haversian system
osteon=central osteonic canal (with blood vessels parallel to long axis of bone) surrounded by lamellae (rings of matrix)
cells=osteocytes in spaces called lacunae
canaliculli- small channels radiating from lacunae to haversian canal
Term
longitudinal bone growth
Definition
epiphyseal plate- cartilaginous discs, near ends of long bones- grows inwards
Term
circumferential growth
Definition
periosteum innerlayer builds concentric layers of new bone tissue-
at same time bone is resorbed or eliminated within medullary cavity
Term
Wolff's law (TEST Q)
Definition
bone responds to the stress placed on it and will remodel to withstand those stresses

-bone strength inc and dec as the functional forces on the bone inc and decrease
Term
remodelling
Definition
resorption of fatigue damaged older bone and subsequent formation of new bone

-new bone laid down at strain sties
Term
Osteocytes
Definition
When osteoblasts become trapped in the matrix they secrete, they become osteocytes.
-sensitive to changes in the flow of interstitial fluid through pores resulting form strain on bone
-boss of osteoblasts and clasts
25% of trabecular bone remodeled each year
Term
bone atrophy
Definition
decrease in bone mass resulting from a predominance of osteoclast activity
Term
bone hypertrophy
Definition
increase bone mass b/c high osteoblast activity
Term
ways to prevent/treat osteoporosis
Definition
early detect- easier to prevent than treat
-optimize peak bone mass in adolescence
-weight bearing PA
diet- ca vit D

factors can contribute:
excessive thinness, smoking, excessive protein/caffine, genetics
Term
female athlete triad
Definition
disordered eating, young female atheletes, amenorrhea (ceesation period)= loss of estrogen=reduced bone density
Term
Characteristics of Female athlete triad
Definition
high incidence of fractures b/c osteoporosis
unsafe weight loss
disorded eating
other psychological variables
can be fatal!
Term
epiphyseal injuries
Definition
growth plate=cartilage cells wh gradually ossify to prod new bone- plate is weaker than surr bone- can terminate bone growth early
Term
how to increase bone density
Definition
-PA to stress bone and bone hypertrophy- need sufficient intensity, weight bearing
DYNAMIC not static loading
heavy weight low rep
varied movements=build overall density
Term
balance
Definition
ability to control equilibrium
Term
base of support
Definition
area bound by the outermost regions of contact between a body and support surface or surfaces
Term
center of mass/gravity
Definition
point around which the mass and weight of a body are balanced no matter how the body is positioned
-balance point of a body as the sum of the torque about this point =0
Term
couple
Definition
pair of equal oppositely directed forces that act on opposite sides of an axis of rotation to produce torque
Term
dynamic equilibrium (D alembert's principle)
Definition
concept indicating a balance b/w applied forces and inertial forces for a body in motion
Term
first class lever
Definition
lever posn with the applied force and the resistance on opposite sides of the axis of rotation
Term
fulcrum
Definition
point of suppt or axis about which a lever may rotate
Term
lever
Definition
simple machine consisting of a relatively rigid barlike body that may be made to rotate about an axis
Term
second-class lever
Definition
lever positioned with the resistance b/w the applied force and fulcrum
Term
stability
Definition
resistance to disruption of equilibrium (both linear and angular acceleration)
Term
static equilibrium
Definition
motionless state characterized by sum of vertical forces=0 horizontal forces=0 and net torque=0
Term
third-class lever
Definition
lever posn with the applied force between the fulcrum and resistance
Term
torque
Definition
rotaty effect of a force about an AOR measured as the product of force and the perpendicular distance b/w the forces line of action and the axis
Term
moment arm
Definition
shortest (perpendicular) distance b/w a forces line of action and an AOR
Term
4 ways to increase stability
Definition
increase mass
widen base of support
lower centre of gravity
bring line of gravity closer to the centre of bOS(base of suppt)
Term
4 elements of balance and stability
Definition
mass
center of gravity
line of gravity
base of support
Term
line of gravity
Definition
straight line from the body's centre of gravity to the middle of the earth- vector for weight
closer line to centre of BOS= more stability
(or shift toward on coming force- increase distance has to move)
Term
when would you want to be unstable
Definition
when athletes want to be ready to move in any direction, quickly as possible- lean with weight in desired direction of motion- LOG to edge of BOS
Term
what is equilibrium
Definition
state of balance b/w two or more forces acting within or upon a body such that there is no change in the state of rest or motion of a body
- all forces are balanced= sum of forces and torques in all directions =0
Term
static equilibrium
Definition
motionless state characterized by sum of all forces and torques =0
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