Mechanics of Human Movement Final

UARK

Define Center of Mass

single point associated with body that if supported, the object will be balanced (dependent on limbs)

What is the difference between balance and stability?

balance: a person’s maintenance of center of mass within base of support

stability: capacity of object to return to original position after being displaced

stability is an act balance is a state

What are the key factors that affect stability?

mass

friction

height of COM

base of support

What are the parts of the axial skeleton?

skull, vertebrae, ribs

What are the parts of the appendicular skeleton?

extremities, shoulder girdle, pelvis

What are the functions of the skeletal system? (biomechanical and physiological)

Biomechanical: levers and support

Physiological: protection, storage of fat and minterals, and blood cell formation

What elements make up bones?

Mineral, Water, and Protein (in order of composition)

What is the difference between cortical and trabecular (cancellous) bone?

cortical: compact, low porosity, shaft of long bones

trabecular: less compact, high porosity, ends of long bones, vertebrae

Define anisotropic. How does it relate to bone?

anisotropic: different mechanical properties depending on direction of load

bone strength depends on load direction

How does bone strength differ between tension, compression, and shear?

strongest to weakest: compression, tension, shear

What is Wolff’s law?

bone strength increases and decreases as the functional forces on the bone increase and decrease

bone in a healthy person will adapt to loads

How does bone density change with age?

decreases with age (Type II osteoporosis)

How does osteoporosis affect trabecular bone?

increase bone porosity (decreases bone density)

Type I and Type II (post menopausal and age associated)

What exercises should you do to assist with bone strength?

Weight bearing exercises (larger forces on skeletal system, greater bone development)

Walk, Hike, Jog, Dance, etc

What is a joint/articulation?

where two bones connect

What are the two functions of a joint/articulation?

provide stability and allow movement

What is the function of articular fibrocartilage?

provide shock absorption, stability, and distribute pressure throughout the joint

Define joint stability

resistance to movement in planes other than those defined by specific joint

What is the difference between tendons and ligaments?

tendon: attach muscle to bone, tensile load to produce joint stability, mechanical pulley and motor control

ligament: connect bone to bone, mechanical joint stability, guide joint motion

How do muscles influence joint stability?

force absorption and muscle contractions increase stability

What is the basic injury model for humans?

No activity increases risk for injury, little to moderate decreases risk, high physical activity high risk of injury (curve)

How does the stress continuum relate to tissue adaptation and injury?

to little stress leads to atrophy in bones, too much stress leads to injury

What is the difference between acute, repetitive, and prolonged injury mechanism?

acute loading: application of single force causes injury to biological tissue

repetitive: repeated application of force leads to stress fractures

prolonged: long duration of applied force leads to injury

What is the model for overuse injury?

adequate rest is needed to build stronger tissue, without adequate rest, overuse injuries occur

What are external and internal risk factors for injury?

external: risk factors related to environment

internal: specific to individual

What are the mechanical properties of fundamental biological tissue?

1. Fibrous Proteins

2. Ground Substances

3. Cells (fibroblast and Chondrocytes)

Mechanical Stress vs Compressive Stress

Stress: External forces by internal forces and cause deformations to the body

Compressive stress: load pushes material more tightly together, collagen and elastin cannot resist compression

What is Strain?

Strain: the quantification of the deformation of a material (changes objects length) (produced by tensile or compressive stress

Tension vs.Torsion

Tensile Stress: When force applied pulls apart a tissue/object, tissue will be deformed by stretch in direction of applied load

Torsion: twisting applied forces

Shear

force applied in both directions, resulting in break

Elastic vs Plastic material behavior

Elastic: stretches under load and returns to original position when removed

Plastic: Permanent deformation of the object occurs

Stiff vs Pilant

Stiff: applying a large load causes small deformation

Pilant: applying a large load causes a large strain

Yield Strength

stress at the elastic limit. no breakage of material occurs, but permanent damage occurs beyond this point

Ultimate Strength

maximum stress tissue is capable of withstanding (micro damage occurs)

Failure Strength

stress where failure occurs (complete tear)

What gives bone it’s elastic properties?

minerals (resist compression)

What are the two types of collagen?

Type I: thick, rugged fibers that elongate with stretched

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

Which fibrous protein resists tensile stretching forces, but has more give when elongated?

elastin (returns to original shape after deformation)

What is ground substance?

water saturated matrix/gel that helps with capturing water and nutrient transport