Chapter 12- Clinical Biomechanics

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Chapter 12- Clinical Biomechanics

• Brendan McElligott
• Kimmi Dotseth
• Joe Kotansky

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Clinical Biomechanics?

• Biomechanics is the study of forces, and their
  effect on living organisms
• Clinical Biomechanics is defined as the
  application of biomechanics to the treatment of
  patients, e.g., by orthopedic specialists or
  physical therapists

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Why does this pertain to us?

• Orthopedists, physical therapists, occupational
  therapists, and athletic trainers are health
  professionals who use biomechanical concepts to
  evaluate and treat patients
• Bioengineers, ergonominists, and human factors
  specialists use biomechanical concepts to
  understand how individuals physically interact
  with their environment

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What this chapter entail?

• In this chapter, the book looks at both statics
  and dynamics, statics is when an object is
  primarily stationary, whereas dynamics is when
  there is movement especially when applied to
  sports and exercise.

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The Scope of Clinical Biomechanics

• Based on content areas of anatomy, mathematics,
  physics, and clinical sciences
• Additional content areas include specific rehab
  techniques, wheelchair design, anthropology,
  specific tissue repair, surgical techniques, and
  architecture

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Kinesiology in Biomechanics

• Kinesiology, the study of human movement, is an
  important content area within biomechanics
• Kinesiology involves the study of the skeletal
  system, including the major joint articulations
  and the major muscles and muscle groups that are
  prime movers during exercise
• This is essential to Exercise Science students
  because they need to know which produce movements
  and why

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Focusing on science in Clinical Biomechanics

• The main property in biomechanics is force, which
  can be defined as a push or pull
• A force that is applied externally to an object
  is a load, when motion occurs, force is the
  factor that causes a mass to accelerate

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Force continued.

• This is shown through the equation F ma
• The exact definition of force however must
  consist of four things point of application,
  line of application, direction of push or pull,
  and magnitude
• All applications of forces and motions on objects
  in biomechanics are subject to Newtons laws of
  motion

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Gravity

• Gravity is the mutual attraction between two
  objects
• The earths gravity on an object is called the
  objects weight
• The earths pull on an object is what we consider
  down

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Contact

• Whenever two object are in contact, a force acts
  between them
• This goes along with Newtons 3rd law
• Forces acting in the body can cause a few
  different adverse things such as compression- the
  process in which 2 forces act along the same line
  in opposite directions toward each other and
  tension, the process in which 2 forces act along
  the same line in opposite directions away from
  each other. The forces tend to pull the object
  apart

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Inertia

• An object at rest tends to remain at rest, and
  an object in motion tends to remain in motion at
  a constant velocity unless acted on by an
  external force. This is inertia

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Muscle

• It is important in biomechanics because it
  generates the bodies forces
• Different times of lifts/contractions mean
  different things in biomechanics
• Isometric contractions are when the muscle force
  is equal to the resistance offered and there is
  no change in length in the muscle
• Concentric contraction occurs if the muscle force
  exceeds the resistance offered and the distance
  between the attachments decreases
• A eccentric contraction occurs when the muscle
  force exceeds the resistance offered and the
  muscle increases in length

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Elasticity

• Is defined as the capacity of an object to reform
  to its original size and shape once it has been
  deformed
• This can be seen through F-kl, where k is the
  material and l is the amount of deformation

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Composition and resolution of forces

• Combining forces is called the composition of
  forces
• The process of dividing forces is called
  resolution of forces
• When 2 or more forces are subjected on an object,
  the single force is called a resultant of the
  forces
• Because forces are vectors, most all forces are
  associated with arrows to which the forces are
  pushing or pulling

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Resolution

• The process of resolution separates the force
  into two perpendicular components
• This can be done either graphically or
  mathematically, often found in geometry

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Equilibrium

• When in equilibrium, the sum of the forces and
  torques equal zero
• Called static equilibrium when an object is at
  rest (Newtons 1st law)
• First Condition
• ? F 0 (sum of forces equal zero)
• Second Condition
• ?M 0 (sum of torques equal zero)

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Second Condition

• ?M 0
• M moment
• OR application of a force at a distance from
  axis
• Since the force does not act through the pivot
  point, the object rotates
• In order to remain in static equilibrium (rest),
  what must happen?
• The ability to determine force components is
  essential to evaluate effects of moment on an
  object

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First-Class Levers (EOR)

• Point of axis (O) between two forces, Effort (E)
  and Resistance (R)
• One force will tend to rotate the object
  clockwise, the other will tend to rotate the
  object counterclockwise
• The distance from the axis can determine the
  magnitude of force needed to keep equilibrium
• Axis force will equal the sum of effort and
  resistance

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Second-Class Levers (ORE)

• Resistance is between the axis and effort
• Magnitude of effort is always less than
  resistance
• Magnitude of force at axis point will always be
  less than then force at resistance
• Example wheelbarrow

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Third-Class Levers (OER)

• Effort between resistance and axis
• Magnitude of effort is always greater than
  resistance
• Resistance will always move faster and farther
  than effort
• Force at axis will be less than at effort
• Works well for throwing or kicking a ball

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Strength of Materials

• Strength of a material is an objects ability to
  resist deformation when a load is placed on it
• Strain- the measure of the change in dimensions
  of an object
• Mechanical stress- the property of a material to
  resist deformation (units are force per unit
  area)
• Three principal stresses and strains tension,
  compression, and shearing

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Stresses and Strains

• Tension two or more collinear forces act away
  from each other
• Material ____________
• Compression two or more collinear forces act
  towards each other
• Material ____________
• Shearing two or more non collinear, parallel
  forces pointed in opposite directions act on the
  material
• Material ____________

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Loads

• Cause stresses and strains to arise
• Axial, bending, and torsion
• May occur alone or in combination
• Compression, torsion, and shearing usually all
  occur to some degree

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Axial Load

• Loading along the axis of an object
• EX Intervertebral disc
• Will mainly have compression stress
• The widening of the disk suggests torsion stress
  as well
• Shearing occurs at 45 degree angle to the loads

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Bending Load

• Forces act in coplanar manner, but not collinear
• EX a beam supported at both ends, or foot
• EX Cantilever
• Compression stress occurs in top part of beam
• Tension occurs in bottom part of beam
• Shearing occurs parallel and perpendicular to
  forces

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Cantilever

• An eccentrically loaded beam
• A horizontal beam is anchored at one end and
  loaded at the other
• EX diving board, proximal end of femur
• Beam tends to bend
• Compression occurs on lower side of beam
• Tension occurs on upper part of beam
• Shearing occurs perpendicular and parallel to
  forces

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Torsion Load

• Rod or shaft is loaded so that it twists around
  the long axis
• EX removing lid from jar, spiral fracture of
  tibia
• Compression and Tension occur along spiraling
  lines
• Shearing occurs perpendicular and parallel to the
  rod

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Effects of Loading on Biologic Tissue

• Wolffs law the ability of the bone to adapt (by
  changing size, shape, internal structure) depends
  on mechanical stresses
• Important in early development
• Too much or too little can be dangerous

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Advances in Clinical Biomechanics

• EMG (Electromyography)- established technique
  that records electrical signal from muscle motor
  units
• Used to determine muscle function
• Can be used to determine appropriate exercise and
  rehabilitation programs
• Ergonomics
• Study of interaction between humans, the objects
  they use and the environments in which they
  function
• Analyze tasks, define risk factors, redesign
  object or environment for increased safety