1 biomechanics/ kinematics/ joint structure/ muscle mechanics/ tissue mechanics

newtons 3 laws

1. an object in motion stays in motion and an object at rest stays at rest unless acted upon by an outside force

2. force = mass x acceleration

3. every action has an equal and opposite reaction

center of mass

the point where the entire mass of an object may be assumed to be concentrated

line of gravity

line that fall from the center of mass

base of support

the area beneath the object or person that includes every point of contact that the object or person makes with the supporting surface and the space in between

vector

a quantity or mathematical object that has both magnitude and direction

magnitude

characterized by length of the arrow

direction

the path where the force is applied

point of application

origin or insertion point of a muscle, center of mass of a bone

force

push or pull that will make an object move linearly

equation for torque

torque = force x distance, that are perpendicular to one another

moment arm

perpendicular distance between the force and the axis of rotation

lever arm

distance between the point of application on the segment and the joint axis

internal force

all the forces created by out muscles or ligaments

external force

all the forces created by gravity, predominantly acting on our bony segments

internal torque equation

internal froce x distance

external torque equation

external force x distance

lever

involves an external force (gravity) acting on a simple rigid system (bones) to create joint movement via an internal force and is used to convert a linear force into a rotary torque

1st class lever

internal force and external force are on opposite sides of the joint axis of rotation (fulcrum)

2nd class joint

internal force and external force are on the same side of the joint axis of rotation but the internal force is farther away from the axis of rotation

3rd class

internal force and external force are on the same side of the joint axis of rotation, but the internal force is closer to the axis of rotation

mechanical advantage

the ratio of the internal moment arm to the external moment arm

mechanical advantage of a 1st class lever

greater than or equal to or < 1

mechanical advantage of a 2nd class lever

>1

mechanical advantage of a 3rd class lever

<1

velocity equation

velocity = angular distance/time

kinematics

branch of mechanics that describes human movement

kinetics

branch of mechanics that describes the effect of forces and torques on the body

kinematic chain

articulated segments of the body, connected by joints, that operate synchronously, so that motion in one segment may influence motion in another segment

kinetic chain

articulated segments of the body connected by joints in which the forces or torques that arise in one segment of the body are transferred to other segments

human movement

the translation of a segments center of mass powered by the contraction of muscles

active movement

due to internal force generation

passive movement

due to external force generation

dynamic movement

appreciates both osteokinematics (bone movement) and arthrokinematics (joint movement)

osteokinematics

describes the motion of bones relative to the planes of the body (always named for the distal segment of the joint)

joint axis of rotation

point about which movement occurs

bones move around the axis rotation of a particular joint

instantaneous axis of rotation

the axis of a joint often shifts with each degree of movement (NOT FIXED) because the relative position between 2 bones changes

plane of movement

planes of movement are perpendicular to the axis of rotation

synarthrosis joint

fibrous or cartilaginous joints that are immovable/slightly moveable

strongly binds bones together or transmits force from bone to bone

diarthrosis joint

synovial joint allows for free movement in uniaxial, biaxial, or triaxial degrees of freedom

elements of a diarthrosis joint

articular cartilage

articular capsule

synovial membrane

synovial fluid

ligaments

blood vessels

sensory nerves

uniaxial joints

one degree of freedom

hinge and pivot joint

biaxial joints

2 degrees of freedom

condyloid, saddle, ellipsoid joints

triaxial joints

3 degrees of freedom

plane joint, ball and socket joint

open kinematic chain

the distal segment is not fixed, and the motion is unpredictable (motion of one segment is independent of the other)

closed kinematic chain

distal segment of the chain is fixed, and the motion is predictable (motions at each segment are interdependent)

Arthrokinematics

the involuntary, physiologic, accessory, and passive motion between articular joint surfaces that is necessary for normal osteokinematic motion to occur

functions of arthrokinematics

improves congruency of joints, increases surface area of joint surface contact to dissipate force/stress, guides osteokinematic motion

open-packed position

minimal congruency of articular joint surfaces, low ligament tension, joint compression and bone contact leads to low joint stability (promotes motion)

close-packed position

maximum congruency of articular joint surfaces, high ligament tension, joint compression and bone contact leads to high joint stability (motion is restricted)

roll

multiple points along one surface contact multiple points on another articulating surface

glide/slide

a single point on one surface comes into contact with multiple points on another articulating surface

spin

a single point on one surface rotates on a single point on another articulating surface

concave-convex rules

convex on concave = roll and glide / slide are opposite

concave on concave = roll and glide / slide are the same

muscle morphology

the basic shape of the whole muscle

how do you generate greater force

recruit more motor neurons

slow twitch fibers

posture/stabilization muscles

fast twitch muscles

power/strength muscles

rate coding

after a motor neuron has been recruited, the force produced is modulated by the discharge rate of sequential action potentials

isometric contractions

force generation with no movement- constant length of muscle fibers

internal torque= external torque

concentric contractions

force generation with joint movement (against the force of gravity) and shortening of the muscle

internal torque > external torque

eccentric contractions

force generation with joint movement and lengthening of muscle fibers

internal torque < external torque

agonist

muscle or muscle group that is most directly related to the initiation and ececution of a particular movement (prime mover)

antagonist

the muscle or muscle group that is considered to have the opposite action of the agonist

synergist

the muscle or muscle groups that cooperates or assists during the execution of a particular movement

stabilizer

the muscle or muscle group that will steady, anchor, or support a bone or body part so that another muscle will be able to contract with a firm foundation

passive length tension

tension depeloped by stretching the non-contractile elements of a muscle

active length tension

tension developed by stimulating the contractile elements of a muscle

active insufficiency

decreased abilituy of a 2-joint muscle to produce or maintain active tension as it reaches its shortest length over both joints, simultaneously

passive insufficiency

decreased ability of a 2-joint muscle to produce or maintain passive tension as it reaches its longest length over both joints, simultaneously

epithelial tissue

provides a covering

nervous tissue

made up of neurons that carry messages to and from various parts of the body

muscle tissue

includes striated muscles that move the skeleton, and smooth muscle, such as the muscles that surround the organs

connective tissue

supports other tissue and binds them together

collagen

most abundant protein in the body, amino acids spiraled in a triple helix molecule called tropocollagen

type I collagen

thick strong fibers arranged in parallel bundles that elongate very little when stretched, high tensile strength

found in: ligaments, tendons, menisci, bone, fascia, and joint capsules

collagen type II

low tensile strength, arranged in meshwork

maintain general shape and consistency, provide compressive strength to resist deformation

found in: hyaline cartilage, articular cartilage, intervertebral discs

elastin

allow tissue to stretch and return to original shape, maintain funtional integrity under cycles of stretch/relaxation

can be stretched/deformed up to 150% of resting length

found in articular cartilage, spinal ligaments, muscle

extracellular matrix

composed of ground substance for stabilization and resist compression and cells for repair and remodel

dense connective tissue

few fibroblasts, lots of type I collagen, limited blood supple, adapt to external stimuli and stimulate synthesis of collagen and GAGs

irregular dense connective tissue

haphazard orientation of collagen fibers, resist tensile forced from multiple directions, found in joint capsule

regular dense connective tissue

ordered fiber arrangement, provide immediate resistance to tension along the length of the tissue, found in: ligaments and tendons

tendons

regular dense CT, provide high tensile strength to bear high loads, transmit large tensile forces between active muscle contractions and the bone into which it inserts, creates movement and stabilization to joints

ligaments

regular dense CT, high tensile strength bear leads in primarily one direction and small tensile loads in other directions, passive guidance of movement, joint stabilization, sensory proprioception

articular cartilage

specialized hyaline cartilage made of chondrocytes and type II collagen fibers, withstand high, repetitive loads, mostly avascular and aneural

fibrocartilage

mix of dense CT and articular cartilage, provide resiliance, shock absorption and tensile strength, stabilize joints, resist tensile and shear forces, lacks perichondrium

bone

type I collagen, provide rigid support and system of levers, large blood supply for remodeling repair and regeneration (Wolfs Law), little deformation, high resistance to compressive loads

load

force that acts on the body

stress

concentration of load over a particular area (load over a cross-sectional area = F/A)

deformation

force acts on an object to change its origional shapre

strain

% change in length or cross section in response to load

toe region

little force, low strain, tissue slack is straightened out

elastic region

greater elongation as deformation of tissues increases linearly with increasing load (stress)

when load is released, tissue returns to original shape

plastic region

permanent deformation of tissue, when load is released, the tissue DOES NOT return to original shape but still able to hold tension

ultimate failure

tissue does not return to original shape and loses ability to hold any tension, point of rupture (usually 8-13% deformation from original length of tendons and ligaments)

viscous

having an internal resistance to strain when stress is applied

elastic

ability to return to original shape after stress is removed

viscoelasticity

time-dependent mechanical property of materials that exhibit both viscous and elastic

characteristics

time dependent strain

When subject to a constant load, the viscoelastic properties of human tissues determine their response to loading over a specific period of time

creep

progressive strain or elongation of a tissue when exposed to constant load over time

stress relaxation

when a tissue experiences a constant strain or deformation over time, the amount of stress that is felt in the tissue decreases over time