Biomechanics
- the study of structure/function of biological systems using mechanics
- the study of mechanics of a living body (forces exerted by muscles/skeleton)
- internal and external forces acting on a body and how those forces affect function
Ligaments
connect bone to bone
tendons
connect muscle to bone
purpose of skeletal system
structural support and controlled movement
fields that utilize it
sport science
occupational (reduce workplace injuries)
veterinary biomechanics
orthopedic (artificial joints/limbs)
Newton’s 3 Laws of Motion
- If no net force acts on a body, body’s velocity cannot change
- Sum of forces on an object is F=ma
- For every action, there is an equal and opposite reaction
Stress
Weird O symbol
Force per unit area
F/A
Pascals
Strain
Weird E symbol
Fractional increase in length of material
Change in L/L
Unitless
Young’s/Elastic Modulus
Stress/Strain
Describes behavior of elastic material
Pascals
Hooke’s Law
Stress=E*Strain
Many materials follow this under small deformations
Yield Strain/Elastic Limit
When a material no longer returns to original shape once load is removed
Further stress results in PLASTIC DEFORMATION (Irreversible change)
Failure/Maximum Stress
Maximum stress that a material can endure without failing (breaking or fracturing)
Elastic vs Plastic Deformation
Elastic deformation means that the material will return to its original state. Plastic deformation means there is irreversible damage. If looking at a graph, plastic deformation occurs after the linear portion
Strain Energy and elastic elongation
- the potential mechanical energy that is added to a material when put under stress
- calculated as area under the stress-strain curve (can use 1/2xy if linear)
- elastic elongation/relaxation means that there is no net energy cost
- energy is lost when deformation goes beyond the elastic limit
Static deformation on solids vs liquids
solids can resist shear stress with a static deformation, fluids will just flow as a result (definition of VISCOSITY)
Compact/Cortical bone
most prominent in long bones, mostly near surface for structure
Spongy/Cancellous/Trabecular Bone
most prominent in rib cage/spine, mostly near the center of the bone to allow for blood vessles, etc
Anisotropic bone vs isotropic behavior of metals
bone has a very directional arrangement of structures that have different properties when tested in different directions. called ANISOTROPIC BEHAVIOR
ISOTROPIC means that they aren’t directional
Law of Laplace
-relates pressure to tension in hollow organs
-change in P=T/r
T:surface tension in wall (force per unit length)
change in P: pressure difference across vessel wall (Pin-Pout)
for spheres: (heart/lung/bladder)
P=2T/r
Cytoskeleton
made of 3 types of protein fibers:
- Actin microfilaments: flexible
- Microtubules: stiffer
- Intermediate filaments: strongest under tension
cells regulate bundling of these to change properties that allow for migration
Muscle contraction
- ATP converted to ADP+Pi and binds to myosin heads
- Calcium ions flood in which forces tropomyosin to move the troponin from the binding sites on the actin
- Myosin binds to the actin and this is what contracts the muscle
