Exercise Physiology

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					An Overview of Muscle
     Contraction

       PED 5230
             The Systems


• Neural
• Muscular
 "He that wrestles with us strengthens
our nerves and sharpens our skill. Our
      antagonist is our helper."
  Edmund Burke, British statesman, 1729-1797
Neural
Neural
Neural
Neural
Neural
Neural
Neural
                Neural
• MOTOR UNIT
• One motor nerve and all the muscle
  fibers it innervates
• Type I - 1:10-100
• Type II - 1:1000s
• All-or-none
Neuromuscular
                 Neuromuscular
•   Choline and Exercise
•   Acetylcholine levels do decrease during prolong exercise
•   Supplementing with choline does maintain Ach levels
•   Some studies show choline improves aerobic endurance
    performance but some studies show no effect; more studies are
    needed.
•   Lecithin/Choline and Health
•   Helps prevent memory loss, Alzheimer's disease, depression, and
    various psychiatric disorders; lower blood cholesterol; and even
    cure liver disease, cancer, and AIDS.
•   There are theories about how lecithin/choline may help against
    some of these disorders, but the clinical evidence is weak or
    nonexistent.
•   Full Article, Berkeley Wellness Letter, July 2002
     "Great ideas originate in the
               muscles."
Thomas Edison, the most famous American inventor
who, singly or jointly, held a world record 1,093 patents. In
addition, he created the world's first industrial research
laboratory, 1847-1931.
           Muscle Facts
• Muscle have several hundred to over 1
  million muscle fibers
• Muscle fibers: 35 – 450 mm long
• A muscle fiber can have 200-300 nuclei
  per millimeter
           Muscle Anatomy

• Epimysium, Endomysium, and Perimysium converge to form
  tendons and are very elastic
Muscle Anatomy
          • Fiber (muscle cell)
             – Myofibrils
                • Myofilaments
                    – Actin
                    – Myosin
Muscle Anatomy
Muscle Anatomy
Muscle Anatomy
Muscle Anatomy
Actin        Myosin
Muscle Anatomy
Muscle Anatomy
              Muscle Anatomy
• PROTEINS
• Actin
   – Actin
   – Troponin I, C, and T
   – Tropomyosin
• Myosin II (twisted golf clubs)
   – Heavy chain – determines fiber type (I, IIa, IIx, or IIb)
   – Light chain
• Titin – largest protein inside muscle; attaches
  myosin
• Nebulin – attaches actin
• Others
   – Alpha-actinin
   – Tropomodulin
               Muscle Anatomy
• SATELLITE CELLS
• Satellite cells were identified over 40 years ago
  through electron microscopy.
• Satellite cells are the committed stem cells of
  adult skeletal muscle.
• Their major function is to repair, revitalize, and
  mediate skeletal muscle tissue and growth by
  differentiating into myocytes.
• Satellite cells are normally non-proliferative.
• They do become active, however, when skeletal
  muscle tissue is injured or heavily used during
  activities such as weight lifting or running.
• Satellite cells are located at the surface of the
  basal lamina of the myofiber.
Muscle Anatomy
         Muscle Anatomy
• Muscle contains 75% water, 5% inorganic
  salts and 20% protein
• Of the protein, 12% is contractile
  proteins and 8% is enzymes, membrane
  proteins, transport channels, and other
  proteins.
• Myosin most abundant protein with
  approximately 300 myosin proteins in
  one thick filament.
       Muscle Contraction
• ASSIGNMENT
• Turn in an outline or listing of the major
  steps (at least 8) of muscle contraction
  written in your own words.
• Univ. Calf. at Irvine
• NISMAT
Quick Time Movie


       • Yellow = Calcium
       • Green = ATP
       • Gray = ATPase

       • Two Quick Time movies
         of the contraction
         process can be download
         at the 5230 Web Page
       • Or, go to SDSU
Slides of the Sliding Filament
            Theory
ADP + P + energy   ADP + P

                   Energized




    New
    ATP
Types of Muscle
  Contraction
         Muscle Contraction

•   TYPES OF MUSCLE CONTRACTION
•   Isometric (static)
•   Concentric (shortening)
•   Pliometric or Eccentric (lengthening)
         Muscle Contraction
• CONCENTRIC
• Myosin swivel
• Actin slide inward
• Muscle force is greater
  than the resistance or
  weight
• i.e. Force (muscle) >
  Resistance (weight or
  outside resistance)
• Therefore, sarcomere
  shortens
          Muscle Contraction

• ISOMETRIC or STATIC
• ’Iso’ = same
• ’Metric’ = length
• Myosin swivel
• Actin does not slide
• Why?
• Force = Resistance
• Therefore, sarcomere
  length doesn’t change
• Example: pushing against
  a wall
            Muscle Contraction

• ECCENTRIC
• Myosin swivel
• Actin may slide inward
  but...
• …ultimately, actin slides
  away from each other.
• Force < Resistance
• Sarcomere gets longer
• Example: lowering a
  weight
       Muscle Contraction
• ECCENTRIC
• Used to control agonist muscle
• Example:triceps lowers dumbbell while
  biceps ’controls’ the lowering.
• Generates greater tension.
  – Causes more damage than other types?
    • Greater repair required…
    • …producing a stronger muscle
    • Also, results in more muscle soreness.
  – Recruits more or different motor units?
       Muscle Contraction

• Concentric - shortening
• Isometric - same length
• Eccentric – lengthening

• With all three, myosin heads swivel.
• With all three, ATP is required.
• The difference is what actin is, or isn’t
  doing.
     Muscle Fiber Types

 "Every morning in Africa, a Gazelle wakes
   up. It knows it must run faster than the
    fastest lion or it will be killed. Every
 morning a Lion wakes up. It knows it must
 outrun the slowest Gazelle or it will starve
to death. It doesn't matter whether you are a
Lion or a Gazelle... when the sun comes up,
           you'd better be running."
                Unknown quotes
       Muscle Fiber Type
• Myofibullar-
  ATPase
  (M-ATPase)
• Succinate
  dehydrogenase
  (SDH)
  Muscle Fiber
     Type
• Myosin heavy
  chain
  – Type I,
  – Type IIa, IIx, IIb
             Muscle Fiber Type
                                                      Figure 18-15
 Type IIb Motor       Type IIa Motor
                                          Type I Motor Unit         Hybrid
 Unit                 Unit
IIb and IIx myosin   IIx and IIa myosin   I myosin heavy      IIb, IIx, and I
heavy chain          heavy chain          chain               myosin heavy
                                                              chain


Fatiguable           Fatiguable           Fatigue Resistant


Glycolytic           Glycolytic           Oxidative
White                Intermediate         Red
Phasic               Phasic               Tonic
Fatigue Curves       (see next slide)
Twitch Response      (see next slide)
Muscle Fiber Type
Type IIb Type IIa   Type I




                             Twitch Response
                             Fatigue Curves
       Muscle Fiber Type
• Twitch response
                    • Fatigue curves
Muscle Fiber Type


       Figure 18-18   • Order of
                        recruitment;
      IIb
                        additive
            IIa




            I
Muscle Fiber Type


                  • Number of
                    motor units
      IIb
                  • Graph showing
                    % of fibers
            IIa
                    used compared
                    to the amount
            I
                    of muscular
                    force
Muscle Fiber Type
     Architectural Factors
• Series - velocity
• Parallel – force
• Pinnation allows for more
  sarcomeres
             Hypertrophy
• Muscle hypertrophy can increase fiber
  diameter to the point where gas and
  nutrient exchange is limited thus limiting
  muscle endurance.

				
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