the application of mechanics to the study of the structure and function of biological systems
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human biomechanics
how forces act on the musculoskeletal system to produce posture and movement, and how tissues react to these forces
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3 kind of mechanics
rigid body mechanics, deformable body mechanics, fluid mechanics
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rigid body mechanics
cannot be deformed, but realistically some deformation may occur i.e bones and limb segments
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2 subdivisons of rigid body mechanics
statics and dynamics
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static
forces acting on bodies that are at rest or static equilibrium
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dynamic
study of bodies in motion, subdivided into kinematics and kinetics
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which laws defines static equilibrium?
newtons first and third law
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newtons first law (inertia)
rigid body will remain at rest unless an unbalanced net force acts on it
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newtons third law
every action has an equal and opposite reaction
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which law defines dynamics?
newtons second law
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newtons second law
acceleration is inversely proportional to the mass of the body
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kinematics
study of motion without analyzing the forces causing the motion
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motion
analyzed by displacement, velocity, and time
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3 classifications of motion
translational, rotational, general
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translational motion
straight or curved lines
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rotational motion
circular motion around an axis of rotation
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general motion
any combination of rotational or translational motion
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kinetics
study of forces that cause or affect the motion of a body
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2 classifications of forces
internal and external
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external forces
applied to an object and act in contact with the object
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internal forces
exist within the object and act to hold the object together in the presence of external forces
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kinetic chain
combination or series of joint movements that make up a larger movement
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2 types of kinetic chains
open and closed
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force
* newtons second law * contact forces or field forces * represented by vectors (magnitude, direction, position/point of application)
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moment
* bending or turning action created when a force is applied to the lever arm and one end of the lever arm is fixed * m = force x perpendicular distance between line direction of force and axis of rotation
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torque
* type of moment that results in twisting or rotation * created by single force or pair of parallel forces acting on a body in opposite directions * m = force x perpendicular distance between line direction of force and axis of rotation * m = force x perpendicular distance between 2 forces
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forces can be classified into 2 categories
orientation or effect
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orientation forces
* normal * tangential * moment * torque * coplanar * colinear * concurrent * parallel, force couple
* perpendicular to contact surface * includes gravitational force
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tangential force
acts on an object in the direction of a tangent to the shape or path of the object
* ie shear
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friction force
* resists motion between 2 bodies in contact and sliding against one another * amount of friction depends on surface quality and finish
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bending and tension
* moment creates bending if the applied force is great enough * torque creates torsion
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coplanar forces
forces occurring in the same 2d plane but not along the same line
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colinear forces
2 or more forces acting along the same line
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concurrent forces
2 or more forces that act or intersect at a single common point but in tensile or compressive directions
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parallel forces
2 or more forces that run in a parallel direction to each other
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parallel: force couple
variation or parallel force where 2 equal but opposite forces cause only rotation around an axis
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levers
rigid structure or body part that pivots at a fulcrum and converts linear force into rotation
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fulcrum
axis of rotation
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moment arm
perpendicular distance between axis of rotation and direction of force
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first class lever
fulcrum lies between effort force and load
* ie seesaw
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second class lever
fulcrum lies at one end, load lies between effort force and fulcrum
* ie ankle
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third class lever
fulcrum lies at one end, load lies at the other with effort force between them
* ie shovel
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lever arm
rigid structure or body part that pivots at a fulcrum and when force is transmitted through the lever, rotation occurs at the fulcrum
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moment arm
perpendicular distance from axis of rotation and the line of direction of applied force
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moment and torque are
vectors because they have magnitude and direction
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magnitude of torque depends on
amount of force applied, length of moment arm, angle of force applied
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center of gravity
point around which the body or body segment is balanced in every direction
* for solid objects, average position of all points in the object * for the body, is about the belly button anterior to s2
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rear wheel placement of wheelchairs affects
cog, propulsion efficiency, and rear stability of the frame
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increase stability by
enlarging base of support
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greater surface area contact =
lower pressure per square unit
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4 types of body tissues
epithelial, muscular, nervous, connective
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connective tissue
* supports and binds tissues and organs in their location * diverse and varies in structure and function * extracellular matrix and a few cells
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types of connective tissue
* specialized (bone and cartilage) * proper (regular dense, irregular dense, and loose)
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fibroblasts
connect tissue
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chondrocytes
cartilage
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osteoblasts
bone growth cells
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osteocytes
* majority of bone cells * imprisoned in lacunae * mechanoreceptor
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osteoclasts
bone resorbing cells
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3 kinds of extracellular matrix
ground substance, macromolecules, fibers
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ground substance
* gel like * resists compression and absorbs shock * medium for molecular substances to travel between capillaries and cells
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2 types of macromolecules
proteoglycans and glycoproteins
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proteoglycans
structural integrity
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glycoproteins
binding and adhesion
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3 types of fibers
collagen, elastin, reticulum
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collagen
* provides tensile strength * resists longitudinal stress, shear and other forces * most common * triple helix structure
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elastin
* elastic like properties * found in skin, lungs, BV * resists deformational forces with elastic recoil and stretch * made by fibroblasts
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reticulum
inelastic
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cartilage
* withstands compressive forces * collagen and high proteoglycan
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bone and tendon
* resist tensile forces * high collagen fiber and low proteoglycan
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dermis
* resists tensile forces * moderate compression * accommodates stretching * collagen and elastin fiber content and low proteoglycan
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proteoglycans are made of
glycosaminoglycan (gag) and protein
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gag and protein
hydrate matrix, stabilize collagen, resist compressive forces
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hyaluronic acid
not technically a proteoglycan but is hydrophilic and abundant in loose hydrated connective tissue
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type i collagen
* 80-90% of all collagen * includes skin, tendon, bone, vasculature, and organs
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type ii collagen
cartilage
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fibroblasts
collagen is made by
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loose ct
* largely proteoglycans * few collagen and elastin * loose arrangement
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dense ct in fascia, capsule, and dermis
* woven network * mostly collagen and some elastin * impact resistant
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dense ct in tendons and ligaments
* parallel fibers * mostly collagen and some elastin * powerfully resistant to axial loading
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edema
* excessive accumulation of fluid within interstitial spaces * problem with fluid distribution, not an excess of fluid
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3 types of edema
localized, generalized, dependent
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localized edema
limited to site of injury
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generalized edema
uniform distribution of fluid in interstitial spaces
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dependent edema
fluid accumulates in gravity dependent areas (ie pitting)
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hydrostatic pressure and osmosis
how does water move between tissues?
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hydrostatic pressure
* generated by pressure of fluid within or outside capillary * usually water flows out of capillaries
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osmosis
* generated by protein in blood plasma or interstitial fluid * usually water flows into capillaries
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hydrostatic pressure
caused by increased BP, vascular malfunction
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oncotic pressure
caused by acute injury, inflammation, or malnutrition
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bone shapes
flat, short, irregular, long
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long bones are composed of
diaphysis, metaphasis, epiphysis, and epiphyseal plate
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2 types of bone
compact and spongy
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compact bone
* 85% of skeleton * typically exterior * haversian system
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spongy bone
* 15% of skeleton * typically interior and ends * contains bone marrow * less complex, lamellae lay in plates or bars called trabeculae * more porous * larger SA
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periosteum
double layered ct surrounding all bone
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haversian system
* compact bone * highly organized into units called osteons that have a central canal surrounded by concentrically arranged lamellae * solid and strong