Biomechanics (tissues) Flashcards
What are the types of forces on the musculoskeletal system?
- Tension
- Compression
- Bending
- Shear
- Torsion
- Combined loading
What is tension?
Forces are from opposite directions
(Pulling two ends apart)
What can overload with ‘tension’ cause?
Sprains, strains, (sometimes) peripheral nerve injury
E.g. hamstring tear
What is compression?
Forces moving in an approximating (similar) direction
(pushing two ends towards e/o)
What can overload with ‘compression’ cause?
fractures
(sometimes) disc damage/nerve compression
E.g. stress fracture of vertebrae, disc herniation
What is bending?
Force that produces tension on one side of the body’s longitudinal axis and compression on the other side
legit just bending
What is shear?
Combination of tension and compression
forces NOT moving in opposite or approximating (similar) directions exclusively
tbh, the forces look like they from opp sides (like upper part has force from side A, lower part has force from side B)
E.g. ACL ruptures
What is torsion?
Force applied in twisting
What is combined loading?
When loading results in more than one type of stress (force)
What is stress?
A physical quantity
An external force
Force per unit area applied to the material
What is strain?
Stresses lead to strain (deformation)
E.g. putting pressure on an object causes it to stretch
Strain is a measure of how much an object is being stretched
How to calculate stress?
Force/cross-sectional area
How to calculate strain?
Elongation/original length
Basically: new length - original length/original length
What is elastic modulus?
calculate = Stress/Strain
indicator of an object’s likelihood to deform when a force is applied
Look at slide 8 of mechanics biological tissues notes (stress-strain curves)
HAVE YOU LOOKED AT IT?
What are the three regions in the stress-strain curve?
- Initial linearly elastic region
- Intermediate region
- Final region
What is initial linearly elastic region?
Where the
slope = elastic modulus
What is the intermediate region?
Exhibit yielding & nonlinear elasto-plastic material behaviour
Strain hardening; entering plastic phase
Basically, being stretched & deformation can become permanent
What is the final region?
Exhibits linear plasticity where slope = strain hardening modulus
Necking
Until failure
What is plastic behaviour?
An object or material has plastic behavior when stress is larger than the elastic limit
Basically, when stress is removed, the object doesn’t return to original (deformation is permanent)
What is uncrimping?
Taking up slack
From slack to straight
E.g. flabby resistance band; you pull it straight BUT not stretched yet
`Look at slide 10 of mechanics biological tissues notes
HAVE YOU LOOKED AT IT?
What happens at the toe phase (0-2%)?
Uncrimping: takiing up the slack (from slack to straight with NO stretch at all)
Macroscopic slack (bc not homogenous)
Needs more force to bring about deformation
What happens during the linear stretch (~2-5%)?
Elasticity (tissues will be stretched according to force applied)
Start of plasticity halfway through (abit)
Therapeutic range (around 4-6%)
Viscoelasticity
Force
Relaxation
Creep
Hysteresis