Skeletal Muscle - Tension

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Skeletal Muscle - Tension

• (2) active tension (muscle activation)
• Excitation-contraction coupling
• Ca2, ATP
• Muscle size (cross-sectional area)
• Muscle length (stretch)
• Rate coding (frequency modulation) motor unit
  recruitment
• Shortening velocity
• Temperature
• Fiber-type
• Reflexes

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Force-velocity relationships types of muscle
contractions

• Isometric -
• muscle length remains constant
• Static mechanics
• SFx,y 0 ST 0
• Isotonic
• Concentric (shortening)
• Eccentric (lengthening)

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Force-velocity relationships types of muscle
contractions

• Concentric Contraction - shortening contraction
• The torque produced by the muscles at the joint
  overcomes resistance to movement
• Inertia and weight of body segments/limb
• Outside contact forces (impact, free weight, etc.)

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Force-velocity relationships types of muscle
contractions

• Eccentric Contraction
• The torque produced by muscles at the joint is
  less than the resistance to movement
• 1. Muscle must produce some tension
• 2. Usefulness
• Braking against a powerful/rapid movement in
  order to protect joints/muscles (co-contraction)
• Ex. Lifting a heavy weight
• Braking against gravity (also protection)
• Ex. Letting down a heavy weight
• Precise movement towards a target
• Ex. Catching a softball

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Force-Velocity Relationship
Isometric Maximum
Eccentric
Force
Concentric

-
0
Velocity
lengthening
shortening
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Torque-angle relationships
maximal

• Eccentric contractions - Protective mechanism
• 2. Muscles ability to produce torque changes
  throughout ROM

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Anatomical Analysis of Movement

• Identify the joints that are moving
• Describe the type of movement (flexion,
  extension,
• abduction, etc.)
• Identify the muscle that may be used during this
  movement type
• Deduce whether these muscle are producing
  isometric, concentric, or eccentric contractions
  or whether the muscle is passive
• First/oldest type of analysis in Exercise
  Biomechanics

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Anatomical Analysis of Movement

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Mechanical Work

• A force applied an object multiplied by the
  displacement of that object in the direction of
  the applied force
• SYMBOL W
• FORMULA W Fd
• UNITS Metric - Joules (J) 1J 1 Nm
  English footlbs
• Exs. Lifting a free weight, riding a cycle
  ergometer, pushing a sled (if frictional force
  measured - dynamometer)

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Mechanical Work

• Problem Calculate the work involved in lifting a
  300 N weight a height of .6 m
• W Fd
• W (300N)(.6 m)
• W 180 Nm 180 J

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Negative Work The direction of muscle force is
opposite the direction of movement. An eccentric
contraction.
Positive Work The direction of muscle force is
the same as the direction of movement. A
concentric contraction.
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Energy

• DEFINITION the ability to produce work. It is
  manifested in various forms
• Motion (kinetic)
• Position (potential)
• Strain (spring)
• Heat, light, sound
• UNITS Joules (J), calories

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Energy

• Types Formula
• Motion (kinetic) Ek 1/2 mv2
• Position (potential) Ep magh
• Strain (spring) Es 1/2kx2
• Heat, light, sound
• UNITS Joules (J), calories

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Mechanical Gross Efficiency

• Efficiency mechanical work/energy
• Most exercises (weightlifting, climbing stairs,
  cycling) 20 efficient!

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Mechanical Efficiency

• Walking and running gtgt20 efficient!
• Why?
• Natural springs (arch of foot, Achilles
  tendon, muscles)

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Strain Energy ApplicationNatural Springs

• For a man with a mass of 70 kg running at a
  velocity of 4.5 m/s, the arch of the foot will
  store about 17 J of energy when the foot is at
  maximum compression.
• Each Achilles tendon plantar flexors stores
  about 35 J of energy.
• Other muscles (ex. quads) store gt20 J of energy
• This equals a return of over 50 of the energy
  expended while running (110 J).
• Energy Savings when recoil force used during
  pushoff

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Mechanical Efficiency

• Walking and running gtgt20 efficient!
• Why?
• Natural springs (arch of foot, Achilles
  tendon, muscles)
• Legs act as a pendulum in locomotion
• f 1/(2?)??(ag/l)
• Where ag acceleration due to gravity
• l distance from axis of rotation to
  center of mass (gravity)
• most efficient running speed will match the
  dynamic pendulum frequency of the limbs
• this is a dynamic frequency which changes as
  joint angles change in a multi-segmented limb
• Aging, stroke, injury, crutches, neuromuscular
  disease decrease efficiency dramatically

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Power

• The amount of work performed in given time period
  (rate of work performed.
• SYMBOL P
• FORMULA P W/Dt Fd/Dt Fv
• strength x speed
• UNITS Metric watts (W) 1W 1J/sec
• English horsepower

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Power and Work Calculation

• GIVEN A person weighing 580 N runs up a flight
  of 30 stairs, each with a height of 25 cm. The
  time for this effort is 15 seconds.
• FIND The work and power done

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Power and Work Calculation
F weight 580 N d 25 cm 30 750 cm 7.5
m t 15 s W Fd (580 N)(7.5 m) 4350 J P
W/t 4350 J/15s 290 watts

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Force-Velocity Relationship
Isometric Maximum
Eccentric
Force
Concentric
-

0
Velocity
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Concentric Force - Velocity Curve
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Power Velocity Curve
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Power and Force Velocity Curves
P W/?t P F d/?t P F v
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Muscle Dynamics

• Strength
• Dead lift
• Bench press
• Lifting a suitcase
• Power
• 100 m dash
• High jump
• Shot put
• Speed
• Badminton swing
• Frisbee throw
• Short shop stab for a line drive

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Energy

• DEFINITION The capacity to do work
• UNITS The same as the units for work (joules)
• Two Forms of motion
• Kinetic Energy
• Potential Energy

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Kinetic Energy

• DEFINITION The energy of motion.
• SYMBOL KE
• FORMULA KE 1/2(mv2) (Kinetic energy equals
  one-half of an objects mass times the square of
  its velocity.)
• For a motionless body, v 0, therefore
• KE 0

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Kinetic Energy Calculation

• GIVEN A ball with a weight of 70 N is rolling
  with a velocity of 3 m/s.
• FIND The kinetic energy of the ball
• m weight / g 70 N / 9.81 m/s2 7.14 kg
• KE 1/2(mv2) 1.2(7.14 kg)(3 m/s)2
• 32.11 J

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Potential Energy

• DEFINITION The energy of position.
• SYMBOL PE
• FORMULA PE magh (Potential energy equals the
  weight of an object times its height above a
  surface to which it could fall.)
• Increasing an objects height increases its
  potential energy.

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Potential Energy Calculation

• GIVEN A ball with a weight of 70 N is resting on
  a shelf that is 2 m above the floor
• FIND The potential energy of the ball
• PE mag h 70 N 2 m 140 J