Question

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Question 4Why can you jump down further than
you can jump up?

• By
• Aaron Barlond, Barbara Worthington, Brady Feutz,
  Steve Wallstrom

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Muscular Contractions

• Isometric contractions
• Isometric
• The muscle contracts without visible movement
• Isotonic contractions
• Concentric
• An isotonic contraction where the muscle shortens
• Eccentric
• An isotonic contraction where the muscle lengthens

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Eccentric Contractions

• One purpose of an eccentric contraction is to
  decelerate the motion of a joint
• Example when landing from a jump the quadriceps
  work eccentrically to decelerate flexion of the
  knee, thus decelerating the limb
• The tension of the contraction may at first be
  less than the force of gravity, allowing gravity
  to pull the body downward, but is sufficient to
  allow controlled lowering of the body

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Tension

• Tension varies with the type of contraction
• Eccentric gt isometric gt concentric
• Difference accounted for by
• Supplemental tension produced by series elastic
  component (SEC)
• Longer contraction time. This allows
• Greater crossbridge formation by the contractile
  components (actin myosin)
• Recruitment of additional motor units
• Tension to be transmitted to series elastic
  component

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Why cant you jump up 10 feet?

• Concentric contraction
• Muscle fiber composition
• Overcoming gravity (inertia)
• Levers

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Concentric Contraction

• Concentric contractions do not produce as much
  force due to less cross-bridge formation in
  myofibirils
• A fast occurring muscle contraction does not
  allow as much cross-bridging, this reduces the
  force out-put generated by muscle fibers

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Muscle Fiber Type

• Type I Slow Oxidative Fibers (SO)
• Type IIA Fast Oxidative-Glycolytic Fibers (FOG)
• Type IIB Fast Glycolytic Fibers (FG)
• Humans typically have a wide variety of fibers
• Average Population 50-55 Type I, 30-35 Type
  IIA, 15 Type IIB
• Can very greatly amongst individuals
• Endurance athletes may have up to 80 Type I
  Fibers
• Explosive athletes may only have 30 Type I
  Fibers
• Relative fiber type composition by muscle
• Soleus- greater amount of Type I
• Gastrocnemius greater amount of Type II
• Vastus lateralis well distributed mix of
  different fiber types

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Inertia Power

• Inertia an objects resistance to motion
• Example
• A person that weights 70 kg, a force greater than
  687 Newtons (Newtons mass x gravity) must be
  exerted for the person to overcome the force of
  inertia
• Power the rate at which a force does work (power
  work/time)
• Main determinate of vertical leap

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Power Examples

• The leg power of a 70 kg man with
• a 15 inch vertical is 95 kgm/sec
• a 25 inch vertical is 123 kgm/sec
• A 35 inch vertical is 145 kgm/sec
• a 45 inch vertical is 165 kgm/sec
• A 120 inch (10 foot) vertical is 280 kgm/sec

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Levers

• There are very few advantageous levers working in
  the human body, therefore humans are not designed
  to produce great forces via the lever system
• First-class mechanical advantage or disadvantage
• Extension of the neck Joint between atlas
  occipital bone forms the fulcrum, weight of the
  anterior portion of the skull provides the
  resistance, and contraction of posterior neck
  muscles provide the effort
• Second-class mechanical advantage
• Plantar flexion of the ankle ball of foot is the
  fulcrum, the bodys weight is the resistance, and
  the gastrocnemius provides the effort
• Third-class mechanical disadvantage
• Flexing the arm at the elbow elbow joint is the
  fulcrum, the weight of the hand and forearm is
  the resistance, and the biceps brachii provides
  the effort

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Analogy

• If you stand at the edge of building it takes
  little effort to shoot a rubber band off of it.
  Gravity will always pull it to the ground and the
  physical properties of the rubber band should be
  able to withstand landing. However, a rubber
  band can only be shot-up as high as both external
  forces and its physical limits will allow.