week 7 Flashcards
what is biomechanics
applying the principles of physics to biological tissues and systems
what is injury (bad and good definition)
bad = the damage caused by physical trauma, sustained by tissues of the body
good = damage sustained by tissues that ultimately result in pain and or loss of function
how does injury occur in an acute manner
when a force applied to a tissue exceeds the margin of safety and passes its tissue tolerance in a rapid manner (one load)
how does injury occur in a chronic chase
multiple loads occur over a set of time that causes tissue tolerance to decline over time decreasing the margin of safety resulting in failure of the tissue at a load that is normally “safe”
why is there benefit in rest and re-growth
biological structures have active cells that benefit from rest and time off in order to allow the tissues to respond over time off and strengthen
what determines the adaptability or ability to heal faster and give examples
blood supply = the higher the blood supply to a tissue the more adaptable which is why muscle can build rapidly and tendons and ligaments take greater time to heal
importance of stress strain stimulus for optimal tissue
an optimal level of loading exists somewhere between the high and low ends as it minimizes the risk of damage to our tissues
- load is too small no adaptations occur or we see breakdown
- load is too large we see breakdown and failure due to decreased tissue tolerance
what is anisotropy and isotropy
anisotropy = tissue properties differ depending on the direction of load and isotropy is the opposite and the tissue will result in the same way despite direction or type of force
what is the human bodies tissue mostly anisotropy or isotropic
anisotropic
what is the elastic region of the load deformation curve
if you apply a load it will deform but as soon as the load is removed the deformation is removed
do we normally stay in the elastic or plastic region of the load-deformation curve and why
elastic since we are constantly under forces on a daily basis we must be able to not be left with permanent deformation
what is the plastic region of the load-deformation curve
a load is applied but when it is removed only some of the deformation is removed, permanent or semi permanent deformation occurs due to micro trauma from the load
what is the toe region on the load-deformation curve indicating
collagen base tissues (ligaments and tendons or skin) that will have slack previous to the elastic region
draw the load-deformation curve include all regions and label
axis load (N) deformation (m)
what is the elastic region in the stress-strain curve
change in stress/change in strain = elastic modulus
units of the axis for stress strain curve
stress = N/m^2
strain = unitless or %
what is the purpose or reason for the stress-strain curve
allows for a normalized comparison between materials or tissues
- important when speaking on quality or health of a tissue
difference between cortical and cancellous bone
cortical is more compact and is not good at deformation due to less space
where as cancellous bone deforms easily and has bridges (trabecular)
does a bone have greater or less mass when it has a smaller cortical area
less
with less cortical area what can be said about its inertia and resistance to bend
greater moment of inertia and increased resistance to bend due to distributed mass further away = greater stiffness
what else is beneficial about a greater cancellous bone
metabolic energy = less energy is needed so lower mass but still has same strength is important
explain Wolff’s law
- governs bone remodeling
- loading characteristics affect how a bone will respond biologically
- bone will get stronger in the direction of applied loads to adapt (this is due to the strain response of the stresses)
- bone will breakdown or re-orb when loading is too low
hooke’s law equation
F = k*d
what does d = in Hooke’s law
deformation
what does k = in Hooke’s law
stiffness (elastic spring constant)
what is Hooke’s law
to relate the amount a tissue deforms to the force applied to it (valid only in the elastic region)
- applying external force creates internal force that is equal which brings it back to its initial space
what is viscosity
a fluids resistance to deformation or damping
what is the equation for viscosity
F= cv or F = -cv
what is viscoelasticity
combing concepts of elasticity and viscosity
- rate dependent stress-strain characteristics
- time dependent
equation for viscoelasticity
F= kd + cv
what does stiffness and damping relate to
stiffness = storage of energy
damping = dissipation of energy
how is viscoelasticity modified
over time = loading and rest will stimulate tissue adaptations changing k and c
short term = muscle contraction modifies tissue stiffness and damping, so force, energy and tolerance
- when activated = stiffer and more viscus when relaxed
what is stability in lay definition
instability is excess or abnormal motion at a joint
what is stability in mechanical definition
if a body part or joint is perturbed away from its current state or motion, will return to that state
spring force equation
PE = 1/2 k x^2
total system PE equation
spring total + Ph where Ph is how high the force is acting above a joint
what is the equation for total energy
energy stored in springs - work done by P
how do you know where or not something is stable or unstable using delta E
stable if delta E > 0 (and muscles have enough stored energy to over come work)
unstable when delta E < 0
what is the best way to asses injury risks
movement should be screened under demanding conditions
