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Clinical Biomechanics

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									Chapter 12- Clinical
  Brendan McElligott
    Kimmi Dotseth
     Joe Kotansky
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
Why does this pertain to us?
• Orthopedists, physical therapist’s,
  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
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
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
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
Focusing on science in Clinical
• The main property in biomechanics is
  force, which can be defined as a push or
• A force that is applied externally to an
  object is a load, when motion occurs,
  force is the factor that causes a mass to
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
  Newton’s laws of motion

• Gravity is the mutual attraction between
  two objects
• The earths gravity on an object is called
  the object’s weight
• The earth’s pull on an object is what we
  consider “down”
• Whenever two object are in contact, a force acts
    between them
•   This goes along with Newton’s 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
• “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
• 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

• 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
Composition and resolution of
• Combining forces is called the composition of
•   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

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

• When in equilibrium, the sum of the forces
  and torques equal zero
• Called “static equilibrium” when an object
  is at rest (Newton’s 1st law)
• First Condition:
  Ʃ F = 0 (sum of forces equal zero)
• Second Condition:
  ƳM = 0 (sum of torques equal zero)
Second Condition
 • ƳM = 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
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
•   Axis force will equal the sum of effort and
Second-Class Levers (ORE)
• Resistance is between the axis and effort
• Magnitude of effort is always less than
• Magnitude of force at axis point will
  always be less than then force at

• Example: wheelbarrow
Third-Class Levers (OER)

• Effort between resistance and axis
• Magnitude of effort is always greater than
• 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
Strength of Materials
• Strength of a material is an object’s 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
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 ____________

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

• Rod or shaft is loaded so that it twists
  around the long axis
  – EX: removing lid from jar, spiral fracture of
• Compression and Tension occur along
  spiraling lines
• Shearing occurs perpendicular and parallel
  to the rod
Effects of Loading on Biologic
• Wolff’s 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
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

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