Mechanics of human movement final part 1

what forces cause injury?

• external—>internal—→injury

how do external forces cause internal forces?

• they impose loads that affect internal structures of the body

do injuries occur when the applied load is > than tissue strength?

• yes

define deformation

• local shape changes due to applied loads

What affects deformation?

• material: properties, size, shape

• force: magnitude, duration, direction

Linear injury model

• incorrect

• as force (physical activity) increase, risk of injury increase

• fails to mention how sedentary lifestyle have risk factors

Ideal loading injury model

• correct

• u shaped

• shows being completely sedentary has risk

• has optimal level that’s needed for living. go higher than that level, risk of injury increase

What are the three biomechanical factors related to injury?

• force, posture, repetition

• subfactors: contact stress, vibration, cold temperatures

All tissues have a failure tolerance. What factors affect failure tolerance?

• sex

• activity level

• age

• diet

• tissue type/composition

how does the failure tolerance differ between old and young people?

• failure tolerance lowers for older people

examples of posture related injuries

• shoulder dislocation

• acl rupture

• Achilles rupture

what are overuse injuries?

• repetitive strain injuries

• occur when people perform the same task over and over again or stay in one posture for a long period of time

Repetitive loading

• repeated application of a relatively low magnitude load

• EX: stress fracture in bone

acute loading

• application of a single force of sufficient magnitude to cause injury in the biological tissue

• EX: traumatic bone fracture

As the frequency (repetition) of loading increases

• the load required to cause material to fail decreases

Model for overuse injuries

• increased training effort —> increased stress to tissue —→ microscopic tears to tissue —→ tissue molding

• if the rate of remolding is greater than the rate of continued tissue damage, the tissue grows stronger. Go back to training

• If the rate of remolding is less than the rate of continued tissue damage, that leads to overuse injury, which then goes back to tissue remolding

How does proper rest affect tissue tolerance?

• tolerance increases

What extrinsic factors affect injury?

• nature of task

• environment

• equipment

• level of participation

• rules

What intrinsic factors affect injury?

• skeletal muscle alignment

• muscle strength

• bone mineral density

• joint alignment

• previous injury history

What are the fundamental biological tissues?

• Fibrous proteins: collagen, elastin

• Ground substance: glycosaminoglycans, solutes, water

• cells: fibroblast and chondrocytes

Type 1 vs. Type 2 collagen

• Type 1: thick, rugged fibers that elongate a little when stretched

• Type 2: thinner fibers that provide a framework for maintaining the general shape and consistency of a structure

Elastin

• resist tensile stretching forces but have more give when elongated

• return to original shape after deformation

ground substance

• water saturated matrix/gel

• helps capture water, nutrient transport

what is stress?

• external force resisted by internal forces and causes deformations to the body

• amount of deformation relates to stress

• Units: N/m²

What fibers perform well under tension?

• collagen

• elastin

when loaded in tension, how will tissue deform?

• stretch or elongate in direction of applied load

Can collagen/elastin resist compression?

• no

What is strain?

• quantification of deformation of a material (changes in objects length)

• produced by tensile or compression forces

Stiffness

• magnitude of force (load,stress) required to deform a material to a certain length

Stiff vs. Pliant

• Stiff: large load, small deformation

• Pliant: small load, large strain

Yield strength

• stress at elastic limit

• no breakage of material

• permanent damage beyond this point

ultimate strength

• max stress tissue can withstand

failure strength

• stress where failure (complete tears) occur