Biomaterials and Mechanical Properties of Soft Tissues: Collagen, Loading, and Injury Mechanisms

What does BMX stand for

biomechanical properties

What type of tissues are discussed in BMX

ligaments tendons muscles capsules

What percentage of soft tissue is cellular material

approximately 20%

What is the primary cell in soft tissue

fibroblast

What do fibroblasts produce

collagen

What percentage of extracellular matrix is water

approximately 70%

What percentage of extracellular matrix is solid

approximately 30%

What makes up the solid component of extracellular matrix

collagen ground substance elastin

What are the main components of ground substance

proteoglycans and glycosaminoglycans

Which collagen type resists tensile forces

type I collagen

Which collagen type is more elastic in nature

type III collagen

Which cell produces type I collagen

fibroblast

Why do different tendons have different collagen compositions

due to the type and amount of load applied

What role do mechanoreceptors play in soft tissue

they sense load and trigger collagen adaptation

What happens to collagen fibres with repeated loading

they re‑orient in the direction of force

What happens to collagen fibres not aligned with load direction

they are more susceptible to degradation

What is compression loading

forces pushing tissues together

Give a compression example in the body

heel pad during running

How does collagen adapt to compression

increased type I collagen to resist load

What is tensile loading

forces stretching tissue apart

Give a tensile example in the body

Achilles tendon

Which collagen type primarily resists tensile load

type I collagen

What is combined loading

compression and tension occurring together

Give a combined loading example

intervertebral disc

What injury mechanism involves compression of the spine

falling onto the bottom

What type of force contributes to ACL injury

tensile force during valgus stress

What is shear loading

sliding or twisting forces

Where is shear commonly seen

rotating the spine

Give an example of shear injury

upper body rotating forward while hips rotate sideways

What is Instron testing used for

measuring load and displacement in tissues

What does Instron testing help create

stress-strain curves

What is in‑situ muscle testing

measuring force production within the body

What two key variables are measured in tissue testing

load and elongation

What is the toe region

initial region where collagen crimp straightens

What causes elongation in the toe region

fibre uncrimping and slippage

What affects the toe region length

fibre orientation and collagen slippage

Why is a long toe region beneficial in muscle

allows stretch without damage

What is the optimal sarcomere length range

approximately 2.0 to 3.5 micrometres

What protects muscle from overstretch

connective tissue such as endomysium and perimysium

Do ligaments normally have a short or long toe region

short toe region

Why is a long toe region bad in ligaments

causes delayed resistance and instability

What happens to the toe region in damaged ligaments

it becomes larger

What is stiffness

change in load divided by change in elongation

What is the elastic limit

point where micro‑damage begins

What happens beyond the elastic limit

plastic deformation

What is elasticity

ability to return to original length

What is plasticity

permanent length change after loading

What happens if tissue cannot absorb applied energy

it tears or ruptures

How does tissue size affect energy absorption

larger tissues absorb more energy

What is stress

force divided by cross‑sectional area

What is strain

change in length divided by original length

Which structures show more strain in the plantar flexors

muscle fascicles

Which structures are stiffer in the plantar flexors

tendon and aponeurosis

How does ligament stiffness compare in young vs old

higher in younger individuals

How does ultimate load differ with age

higher in younger tissue

Where do older tissues usually rupture

mid‑substance

Where do younger tissues usually rupture

near muscle-tendon junction

How does tissue respond to fast stretch

stiffer response and higher load

How does tissue respond to slow stretch

more compliant response

What injury is more likely with fast stretch

mid‑substance tear

What injury is more likely with slow stretch

avulsion injury

What happens to collagen with immobilisation

becomes disorganised

What happens to tissue strength with immobilisation

decreases

What happens to fibroblast shape with immobilisation

becomes altered

What are two treatments for Achilles tendon rupture

surgery or casting

What tissues are affected by Achilles immobilisation

ankle ligaments foot muscles tibial muscles

How does energy storage change after Achilles rupture

reduced on affected side

Approximately how much less energy is stored

more than 20%

What is creep

gradual lengthening of tissue under constant load

What causes creep

collagen sliding and fluid redistribution

Where is creep seen clinically

lumbar spine and prolonged postures

What is cyclic creep

intermittent loading and unloading

Why do physiotherapists prefer cyclic creep

reduces excessive tissue deformation

Give an activity that involves cyclic creep

jogging

What is stress relaxation

reduction in force over time with constant length

Give an example of stress relaxation

holding a plantar flexor stretch

What happens to collagen during stress relaxation

uncrimping and sliding

What happens to water and proteoglycans during stress relaxation

redistribution occurs

What is collagen sliding

fibres moving past each other at micro‑levels without failure

How long should stretching be for optimal force reduction

approximately 20 seconds

What happens if stretching lasts longer than 90 seconds

muscle performance can decrease

Which stretching type is more detrimental to performance

static stretching

What material behaviour do ligaments and tendons display

viscoelastic

What influences a tissue's ability to withstand load

size and architecture

How do injury and disuse affect tissues

they alter biomechanical properties