Biomechanics

Question 1

Definition of Tensile strength

Answer 1

Max pulling-type stress a material can support before failure

Question 2

Definition of stress

Answer 2

Force divided by area.

Units Nm or Pascal

Question 3

Name and example of a material with high tensile stress and explain function.

Answer 3

A tendon. Needs high tensile strength so it can transmit muscle force to bone without self breaking. Allows for movement.

Question 4

Explain deformation

Answer 4

When a solid material is applied force, it can move or it can deform.

It is local displacement of material from old to new position.

Question 5

Define a strain

Answer 5

A strain is change in dimension divided by original dimension.

Has no units.

Question 6

What is the definition of max stress applied

Answer 6

Measure of strenght.

Units: N/m2 or pascals

Question 7

Definition of extensibility

Answer 7

Max strain. Has no units but can use %.

Question 8

How do one measure stiffness?

Answer 8

Slope or gradient of loading line and has same units as stress.

Question 9

How to measure toughness

Answer 9

Area under gradient of loadingline (from stiffness) makes energy to break the material. Units is joules.

Question 10

What is flexural stiffness?

Answer 10

Measure resistance to bending = EI

Question 11

Compare collagen and elastin

Answer 11

Collagen

• 100 kPa
• Stiffer
• 10% extensibility
• arteries, tendons

Elastin

• 200% extensibility
• 20 mPa strenght
• skin

Question 12

Centre of movement when walking and running

Answer 12

COM lowest in walking when double contact, and highest when one supporting leg.

Running highest during aeral phase and greatest velocity dring aeral phase.

Question 13

Explain proteoglycan

Answer 13

Large and branched molecule consisting of both proteins and carbohydrates. Negative loaded because of the negative sulphate groups on keratin branches.

Question 14

Explain work compared to moment

Answer 14

Force x displacement, and displacement is parallell to force applied.

Where moment= force x arm length, and rotates relative to specific rotation. Perpendicular.

Question 15

Describe elasin

Answer 15

Is a protein consistent of hydrophilic compartments giving them a beands on a string apperance.
The high extensibility is due to high extensibg of coiled fibres
High elasticity is when hydrophilic is in contact with water so want to return to earlier state.
Low stiffness?

Question 16

What is creep?

Answer 16

Property of viscoelastic materials. Means continued increase in strain over time though applied stress remains constant value over time.

Question 17

What is the definition of strenght?

Answer 17

Max stress a material can endure.

Question 18

Name 4 abilities if articular cartilage

Answer 18

Sustain load by absorbinf energy
Friction reducing
Maintains joint stability
Type 2 fibres and proteoglycan molecules
Has different zones

Question 19

What is a stride?

Answer 19

Equals two steps. 1 full gait cycle of heel strike, foot flat, midstance, heel off, toe off.

(Stance and swing 60/40)

Question 20

Determinations of gait

Answer 20

Pelvic tilt in coronal or saggital plane
Valgus deformity
Knee flexed
Foot or ankle interactions

Question 21

Explain centre of mass in walking

Answer 21

Greatest forward velocity during double support phase and COM greatest gravitational energy when single leg support.

Question 22

Explain the stages of swing phase

Answer 22

Acceleration, midswing, decleration

Question 23

Explain how energy cost can be kept constant at a certain velocity during running

Answer 23

Conversion of potential and kinetic energy temporarly to elastic strain energy.

Tendons allow for mechanical energy to be stores as strain energy, thereby returning it when recoiled.