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What are the 5 characteristics mentioned about the Biomechanics of the hip?

  1. Ball and socket joint {The number 1 as a lacrosse stick}
    1. Ball = Head of femur
    2. Socket = Acetabulum {Imagine Ace’s first fists shooting out of either side of my hip}
  2. Must withstand the mechanical stress that comes from compression by both body weight and muscles {2 getting compressed}
  3. The Hip must be able to withstand forces 6x that of walking. {3 in a baby chair crying and failing because he doesn’t want to eat his 6 soup, with Drake on the cover.}
  4. The femur heads protruding orientation allows for a greater range of motion {Four: WHORE’S love that long stroke motion, where the tip almost leaves the poon)
  5. Hip fractures have a high mortality rate because of the threat posed to internal organs during operation {Five: People can DIE if the replacement surgery has a hiccup.}
    1. Risk factors include:
      1. Age
      2. Incidence of fall
      3. Osteoporosis: reduced bone density
      4. Female gender


What are the two characteristics mentioned about the interior structure of the femur?

  1. Trabecular bone {One: SpongeBob lifting a weight weighing one TON}
    1. Its arrangement allows it to be spongy light and strong.
  2. “Wolff’s Law” {two: the wolf cyborg says OW WOOOO in response to the stress of the operation that is attempting to restructure his bones}
    1. Mechanical stress is responsible for determine the architecture of the bone


What are the 2 characteristics given about Knee Biomechanics?

  1. Composed of two “sloppy” joints {One: Noe was SHUNNED from future sessions because he would always only provide two sloppy joints.}
  2. Three forces acting on patella:
    1. Contact with the distal end of the femoral bone
    2. Tendon force coming from the quadriceps tendon
    3. Tendon force come from the patellar tendon


What are the 3 characteristics given about the meniscus?

  1. Rounded fibrous cartilage between tibia and femur {Mini-kiss lips on the proximal end of the tibia and distal end of the femur kissing each other}
  2. Reduces pressure at the meeting point by increasing surface area
  3. Provides stability by restricting motion


What are the 2 details given about ACL ruptures?

  • Unhappy triad:
    • Tear in the ACL, MCL, and Medial Meniscus
    • Caused by a lateral (outside) impact to the knee
  • Muscles resist only 17% of the force, the rest of the 83% is handled by the ligaments


What are the conflicting requirements for the foot and ankle?

  • Has to be able to bear a heavy load requiring stability and rigidity
  • However, it must also be flexible and conforming to allow for better traction, balance, leverage, and proprioception.


Describe the arches of the foot.

  • Combining all three of the arches of the foot make a dome shape
  • The arches are supported by both intrinsic and extrinsic muscles, the plantar aponeurosis, and ligaments.


What is a flatfoot deformity? What is it caused by? How is it treated?

  • The dome shape created by the arches collapses
  • Could be a result of slackness or tearing of posterior tibial tendon
  • Treatment
    • Orthotics or surgery to repair the torn tendon


What are the 5 articulations of the shoulder?

– acromio-clavicular
– coraco-clavicular
– gleno-humeral
– sterno-clavicular
– scapulo-thoracic

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Why are large muscle forces necessary at the shoulder?

  1. Arm weights have large moment arms
  2. Muscle forces have small moment arms

So great force must be generated to overcome the difference in the two moment arms.

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The tendons of which 4 muscles form the rotator cuff? What are the functions of these muscles?

  1. Subscapularis
  2. Supraspinatus
  3. Infraspinatus
  4. Teres Minor
  • Rotators of the humerus
  • Pulls head of humerus into glenoid fossa
  • Contributes to stability

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What is rotator cuff syndrome? What are 2 possible causes?

  1. Impingement of RC tendons which leads to inflammation and tearing
  2. Possible Causes
    • Narrow space between the acromion and humeral head
    • Stretched RC tendons let deltoid draw humeral head up too high.

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What are the 3 stages of Rotator Cuff Syndrome? How can they be treated?

  • Stages
    1. Edema and/or hemorrhage, reversible, due to overuse (25 years of age)
    2. Evident fibrosis, irreversible (25-40 years of age)
    3. fibrosis and tendinosis, irreversible (over 50 years of age)
  • Treatments
    1. Anti-inflammatories and ice
    2. removal of acromial bone spur
    3. surgical repair of tendons

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Explain the structure of the elbow.

  • Three Articulations
    1. Humeroulnar - hinge
    2. Humeroradial - gliding
    3. Proximal radioulnar - pivot
  • Olecranon process of ulna
    1. Increases triceps moment arm when elbow is extended
    2. Allows you to hold heavier objects when the arm is extended

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What is the "Carry Angle"? How does it differ by gender?

  • Normal Valgus angle formed between upper arm and forearm
    1. Appears in frontal plane with the palm facing forward
  • Differs by gender
    1. 10-15 degrees in men
    2. 15-20 degrees in women

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Explain the structure of the wrist and the hand.

  1. Carpals, Metacarpals, Phalanges
  2. Articulations
    • Radio- and ulnocarpal
    • Carpometacarpal (CM) - Not Movable!
    • Metacarpophalangeal (MCP) - Movable!
    • Interphalangeal (IP) - Movable

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What is the carpal tunnel?

  1. Beneath flexor retinaculum
  2. Carries median nerve and nine flexor tendons

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What is carpal tunnel syndrome?

  • Symptoms: Numbness, tingling in the thumb, index, and third finger
  • Caused by the median nerve being pressed against flexor retinaculum

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Why has the rate of Carpal Tunnel Syndrome (CTS) increased in the last 30 years?

More people use computer keyboards which are more damaging than typewriters due to:

  • being a flat surface
  • permitting uninterrupted typing
  • workers tend to use more force than necessary


What are 3 characteristics of facet joints?

  • Change orientation
    • From cervical to lumbar regions
    • Allow rotation at mid-thoracic or higher
  • Allow smooth articulations between vertebrae
  • Resist motion
    • Through bony interactions
    • Resist rotation at thoracolumbar junction and below
      • allow flexion/extension

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Describe the vertebral structure.

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Which bones commonly suffer from systems of osteoporosis?

  1. Spine
  2. Wrist
  3. Calcaneus
  4. Hips


Who is most commonly affected by osteoporosis?

  1. Thin build
  2. Smokers
  3. Caucasians or Asians
  4. Women
  5. Post-Menopausal
  6. People exposed to microgravity


How much bone mass is lost in space?

  • 2% per month
  • People can exercise in space with special equipment that must be lighter since it is expensive to send heavy things to space.


What are some causes of lower back pain?

  • Sprains (ligaments) & strains (muscles & tendons)
  • Age-related generation
  • Disc injury

Most frequent cause of lost work days for those younger than 45.


WHat are Intervertebral discs composed of?

  • Annulus Fibrosus
    • Fibrous tissue
    • Resists
      • torsion
      • Compression
  • Nucleus Pulposus
    • Gel material
    • Resists
      • Compression

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What part of the spine has to carry the heaviest load

The lumbar region

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In order of least to greatest disc pressure, rank the 5 positions mentioned in the lecture.

  1. Laying down flat
  2. Standing up straight
  3. Sitting down straight up
  4. Standing up bent over
  5. Sitting down bent over

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Why is degenerative disc disease a problem?

  • the load primarily passes through the annulus instead of both the annulus and the nucleus.
  • this causes concentrated end plate loading instead of the healthy distributed end plate loading.


What is Anthropometry?

Measurement of the human body.


What is anthropometry useful for?

  1. Biomechanical analysis of human motion
  2. Design of devices requiring human interaction


Define mass

Amount of matter in a body; property describing a body's resistance to acceleration.


Center of mass

Balance point; point about which free rotation occurs


Moment of inertia

Property describing a body's resistance to angular acceleration; increases as mass is located father from the axis of rotation


What are the inertial properties?

  1. Mass
  2. Moment of inertia
  3. Location of center of mass


What does COM depend on?

Body position.


How can you find a body's COM using segment COMs

Find the weighted average of the segment COMs

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Why did LeBron appear to hang in the air?

  • By changing the position of his body he changed the position of his center of mass. 
  • His center of mass maintained a parabolic trajectory despite his body appearing to defy physics.



State the parallel axis theorem.

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What are the 3 commonly-used methods for determining body segment mass? what are some assumptions and problems that these methods create?

  1. Regression models based on cadaver measurements
  2. Geometric models
  3. Medical imaging techniques
  • ALL methods assume segments are rigid bodies
  • Segment definitions are sometimes uncertain
    • What do you mean by "thigh", somewhat arbitrary isn't it? this can lead to inconsistencies in measurements
  • Anthropometric measurements are often based on anatomic landmarks which may be difficult to locate
    • Leads to very rough estimations that create a lot of uncertainties and calculations


What are regression models?

Equations that predict inertial properties from anthropometric measures such as stature, body mass, segment lengths, segment circumferences.


  • mFOREARM = 0.06 mB
  • xCOM-THIGH = 0.433 LTHIGH (43% from proximal to distal)


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How are the cadavers that are used to create regression models prepared? What are the disadvantages to this method?

  1. Cadaver cut into segments, frozen, then:
    • Weighed (to find mass)
    • Balanced on a knife-edge (center of mass)
    • pendulum tested (moment of inertia)
  2. Disadvantages; difference between living and dead tissue
    • Frozen tissue is rigid
    • Fluid is lost
    • Fluid pools


How are geometric models used.

  • a body part is modeled after a geometric shape with known equations for its dimensions
  • Density must be assumed to be the same throughout the segment
    • this is a problem because density is not consistent throughout any body part.


What are image-based Techniques? what are there advantages?

  1. Uses sophisticated medical imaging
    • computed tomography (CT or "cat scan")
    • magnetic resonance imaging (MRI)
  2. Permits measurement of tissue shape and local density
    • Extra density and shape information allows for more accurate geometric model to be constructed.


Why measure motion?

  • Motion sometimes to fast to assess with the naked eye
  • Accelerations may be used to compute joint moments and forces - "inverse dynamics"


What are 4 uses for motion analysis?

  1. Assessment of athletic performance
  2. Diagnosis of movement abnormalities
  3. research tool
  4. entertainment


What is so special about the lord of the rings?

It was the first time motion capture technology was used in a film.


Where are markers placed in motion analysis?

  • Markers are placed on bony landmarks and are used to establish anatomical coordinate systems.
  • It is assumed that marker motions are the same as bone motions


What are the 3 forms of motion Analysis?

  1. Two-dimensional (e.g., MaxTRAQ)
    • Requires two markers per segment
    • one camera
  2. Three-dimensional 
    • three markers per segment (not in line)
    • two (or more) cameras are needed to plot the data in a 3D space.
  3. Manual or automated
    • refers to identification markers
    • computer does the work but this is expensive

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What is the purpose of calibration?

  • Calibration tells the system where the cameras are and how they are coordinated
  • Allows for ray equations to be derived.

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Explain reconstruction in 3D motion analysis.

  1. Process of determining actual coordinates (3D) from image coordinates (2D)
  2. Actual coordinates are "reconstructed" from image coordinates obtained from each camera
  3. Involves solving systems of ray equations.


  • Calibration produces ray equations
  • Reconstruction uses the ray equations to transform 2D images into 3D coordinates


Provide 4 characteristics of automated motion analysis.

  1. Markers are necessary
  2. Markers may be passive (reflective) or active (light-emitting)
  3. A computer performs marker identification and reconstruction
  4. Use of multiple cameras
    • reduces the possibility of marker "drop-out" (obstruction)
    • increases accuracy by allowing for averages


What are the other Systems of motion tracking?

  1. Electromagnetic systems
    • Movement occurs in a magnetic field
    • The sensor is attached to each limb segment
    • Electromagnetic interference (EMI): Metal in field interferes with the measurement
    • Wires may restrict movement
    • e.g., "Flock of Birds"
  2. Electrogoniometry
    • "gonio" (angle) + "meter" (measure)
    • Mechanical linkage with sensors attached to joint

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What is Ground Reaction Force?

  • Force applied by the ground to the foot
  • Equal and opposite to force applied by foot to ground (3rd Law)
  • Uniquely related to acceleration of whole body COM:
  • Broken into vertical and horizontal components

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Explain the force diagram for walking ground reaction force.

  • "Double-Bump"
  • First bump represents weight acceptance
  • Second bump represents push-up 

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Explain the shape of the running ground reaction force graph.

  • Early peak 2.2BW
    • Deceleration of foot and lower leg
  • Late peak of 2.8 BW

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What is a transducer? provide 4 examples.

Device or material that converts one physical variable into another


  • Thermometer > Temperature into fluid volume
  • Photocell > Light intensity into voltage
  • Microphone > sound waves into voltages
  • Speaker > Voltages into sound waves


How is a bathroom scale an example of a Transducer?

  • It gives a reading of the force being applied to it
    • It is reading the extension of the spring inside of the scale
  • Force converted to displacement
    • dependent on Hooke's Law: F = kx

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What are strain gauges? How do they work?

Transducers whose electrical properties change when they are stretched.

How does this work?

  • Current flows less readily through wires that have been stretched
  • Strain gages a small wire glued to something whose deformation must be monitored


How do force plates work?

  • Strain gauges are located at each corner
  • Force plate supports are deformed when foot is on plate
  • Deformation at corners directly related to force applied
    • Hooke's law is important once again, F = kx
    • Electrical resistance of strain gauges is measure

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What is the center of pressure (COP)? How can strain gauges tell us where COP is?

  • The point at which GRF would act if GRF acted at a single point

Use of multiple strain gauges gives information about the location of the COP


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Explain the two classifications of error.

  1. Systematic error
    • Affects repeated measurements in the same way
    • Reduces accuracy
    • easier to correct, relies on finding the source and nature of the error
  2. Random error
    • Varies unpredictably with each measurement
    • Reduces precision
    • Also called noise
    • as opposed to "signal", the data of interest


What is the difference between accuracy and precision?

Accuracy is how close you were to hit the target on average.

Precision is how similar each trial was.

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How does Low-Pass Filtering work?

  • Eliminates high-frequency noise above "cut-off frequency"
  • Saves (lets pass) low-frequency signal below cut-off
  • Frequency measured in hertz (cycles/sec)
    • Typical cut-off frequency of 5 Hz in motion analysis
  • May result in loss of signal when signal is rapidly varying - ex/ Heelstrike GRF transition

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What are the three ideal force plate characteristics?

  • Strong to withstand high forces
  • Rigid to feel like the floor
  • High natural frequency (depends on force plate and connection to floor)


What does a low-frequency force plate result in?

Errors due to oscillation


What type of frequency would jello, rubber, and steel have?

  • Jello: Low natural frequency
  • Rubber: Higher natural frequency
  • Steel: much higher natural frequency


What is a High sampling frequency in relation to force measurements?

Capacity to make many rapid force measurements


Is GRF of the foot in one central location?

  • No, it is spread out across the surface of the entire foot
    • High in some places, low in others


What is a pedobarograph?

Device with many small force transducers for reading pressure distribution over the foot surface.


Why is it important to measure the pressure distribution during walking?

  • Aids in the selection, modification of footwear


What is diabetic neuropathy? How does this affect diabetics? What does this result in?

  • Loss of protective sensation in extremities
  • Diabetics unable to detect stimuli that ordinarily would cause pain
  • Results in ulcers, amputations


Explain a load cell force transducer?

Measures force in one direction (uniaxial) or multiple directions (multiaxial)


Explain an instrumented prosthesis.

Hip or knee replacement fitted with small load cell


Describe a buckle transducer.

Measures force being applied to a tendon by using a buckle shaped attachment. 


Where is the buckle transducer placed when measuring walking forces? What size incision does the placement of this transducer require? Is anesthesia used?

  • On the Achilles tendon
  • Requires 5-inch incision
  • No anesthesia


What is the peak force measured during walking?

3000N (3-4 times body weight)


How do fiberoptic force measurements work?

Force carried by tendon or ligament squeezes fiberoptic cable, cutting off light transmission which allows tendon force to be measured in relation to the amount of light being disallowed.


What are impacts occur? describe the duration?

  • When bodies collide
  • Large force applied over a short period of time


Why do we care more about the before-after change in velocities of objects involved in an impact?

Because time of the impact is very short


What are the two types of impacts, give examples of each.

  • Elastic: relative velocity unchanged by impact
    • Golf ball bouncing on cement
    • e (coefficient of restitution) = 1
  • Plastic: relative velocity is zero after impact
    • Ball of clay striking wall
    • e = 0


What does the coefficient of restitution relate? what does it depend on?

  • Relative velocities
    • depends on materials, shapes, temperatures


what is the formula for coefficient of restitution?

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What is impulse? (2)

  • Force exerted over time; F x t
  • Change in momentum (mass x velocity)


Does the change in momentum depend on time force is applied? what does this mean?

  • Yes
  • Impulse dictates change in momentum


What do negative impulses do to momentum?

Reduces it.


How is impulse computed using a Force x Time graph?

finding the area under the curve.