Physiology of Strength Training

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Physiology of Strength Training

• Part 2 Muscle Contraction (continued)

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Types of Contraction

• Isometric (static)
• Concentric (shortening)
• Pliometric or Eccentric (lengthening)

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Concentric Contraction

• Traditional contraction
• Myosin swivel
• Actin slide inward
• Muscle force is greater than the resistance or
  weight
• i.e. Force (muscle) gt Resistance (weight or
  outside resistance)
• Therefore, sarcomere shortens

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Isometric or Static Contraction

• Iso same
• Metric length
• Myosin swivel
• Actin does not slide
• Why?
• Force Resistance
• Therefore, sarcomere length doesnt change
• Example pushing against a wall

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Eccentric Contraction

• Myosin swivel
• Actin may slide inward but...
• ultimately, actin slides away from each other.
• Force lt Resistance
• Sarcomere gets longer
• Example lowering a weight

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Eccentric Contraction II

• Used to control agonist muscle
• Exampletriceps 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?

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Types of Contraction Summary

• 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 isnt doing.

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Muscle Structure and Neural Control

• Chapters 17 and 18

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Factors That Influence Acute Strength Production

• Size
• Length prior to contraction
• Speed of contraction
• Joint angle
• Architectural factors
• Stimulation
• Motor units
• Fiber type

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1. Fiber Size
Why are larger muscle fibers stronger muscle
fibers?
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2. Length-Tension

• Figure 17-23
• Without considering the elastic properties,
  greatest strength will occur with optimal overlap
  of the thick and thin filaments
• Active force
• Passive force
• Pre-stretching adds an elastic
  component
• Muscle spindles

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Muscle Spindles

• Respond to sudden changes in muscle length
• Can produce a reflex involving motor neurons and
  the shortening (contracting) of the muscle
• Reflex continues for about 10 seconds
• They are also used to control movement

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Muscle Spindles
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2. Length-Tension Summary
Elastic/Spindles Actin/Myosin
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3. Speed of Contraction

• Slower contractions are stronger contractions
• Considering the sliding filament theory for
  muscle contraction, why would slower contractions
  be stronger contractions?

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4. Joint Angle
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5. Architectural Factors

• Series - velocity
• Parallel force
• Pinnation allows for more sarcomeres

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6. Stimulation

• Myelin and the speed of contraction (MU size)
• Some neurons stimulate, others inhibit (GTO)
• Action potential is the sum of all stimuli
• All or none

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Stimulation

• Twitch
• Summation
• frequency of stimulation
• Tetanus
• Synchronization

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Stimulation
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7. Motor Units

• Motor nerve and all the muscle fibers it
  innervates
• ST - 110-100
• FT - 11000s
• All-or-none

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Motor Unit/Fiber Types

• Figure 18-15

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Motor Unit/Fiber Types
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Motor Unit/Fiber Types

• Fatigue curves
• Twitch response

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Motor Unit/Fiber Types

• Order of recruitment additive

Figure 18-18
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Motor Units

• Number of motor units
• Graph showing of fibers used compared to the
  amount of muscular force

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8. Fiber Types
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8. Fiber Types

• Myosin heavy chain (meromyosin)
• ATPase
• Type I,
• Type IIa, IIx, IIb

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Fiber Types
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Fiber Types

• Can they change?
• Is the ratio of FT to ST the same in all muscles?
• How much does the ratio of FT to ST influence
  performance?

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Fiber Types
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Fiber Types
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Fiber Types
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Acute Strength Production

• Size
• Length prior to contraction
• Speed of contraction
• Joint angle
• Architectural factors
• Stimulation
• Motor units
• Fiber type

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Other Neural Factors
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Golgi Tendon Organs

• GTO are stimulated during intense contractions or
  high muscle tension
• Their reflex inhibits further muscle contraction
  or tension
• PNF

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GTO
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PNF

• Proprioceptive Neuromuscular Facilitation
• Contract muscle to stimulate GTO
• GTO cause muscle to relax
• Stretch relaxed muscle further

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Control of Movement

• Origin of movement
• Cerebral cortex
• Spinal reflexes
• Muscle spindles
• Golgi Tendon organs
• Figure 18-28

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Other Matters
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Acute Cardiovascular Responses

• Upper body exercise and/or isometric contractions
• Increase sympathetic stimulation
• Increase in heart rate
• Increase in blood pressure
• Increase work of the heart

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Acute Cardiovascular Responses

• Valsalva Maneuver
• Exertion with a closed glottis
• Increase intro-abdominal pressure from
  contracting muscles (abs and diaphragm)
• Decrease venous return to the heart (pre-load)
• Decrease stroke volume and thus cardiac output
• Ischemia, dizziness, etc.

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Low Back Pain

• 60-80 of people experience back pain
• Little strong evidence that regular exercise will
  significantly reduce the risk
• Prevention
• Strong abdominal muscles to add support
• Axler, CT. Med. Sci Sprt Exer., 29804, 1997.
• Flexible hamstrings
• Weight loss to decrease resistance
• Warm-up to increase elasticity and blood flow

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Axler, CT. Med. Sci Sprt Exer., 29804, 1997.
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Axler, CT. Med. Sci Sprt Exer., 29804, 1997.

• No one exercise is best for strengthening the abs
  with low lumbar stress
• Partial curl-ups came closets (D)
• Several exercises are required to train the
  entire abdominal muscle area
• Not recommended are straight or bent-leg raises
  (G F), static cross knee curl-up (I), handing
  bent-leg raise (K)

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THACKER, S. B., J. GILCHRIST, D. F. STROUP, and
C. D. KIMSEY, JR. The Impact of Stretching on
Sports Injury Risk A Systematic Review of the
Literature. Med. Sci. Sports Exerc., Vol. 36, No.
3, pp. 371-378, 2004.

• Purpose We conducted a systematic review to
  assess the evidence for the effectiveness of
  stretching as a tool to prevent injuries in
  sports and to make recommendations for research
  and prevention.
• Methods Without language limitations, we
  searched electronic data bases, including MEDLINE
  (1966-2002), Current Contents (1997-2002),
  Biomedical Collection (1993-1999), the Cochrane
  Library, and SPORTDiscus, and then identified
  citations from papers retrieved and contacted
  experts in the field. Meta-analysis was limited
  to randomized trials or cohort studies for
  interventions that included stretching. Studies
  were excluded that lacked controls, in which
  stretching could not be assessed independently,
  or where studies did not include subjects in
  sporting or fitness activities. All articles were
  screened initially by one author. Six of 361
  identified articles compared stretching with
  other methods to prevent injury. Data were
  abstracted by one author and then reviewed
  independently by three others. Data quality was
  assessed independently by three authors using a
  previously standardized instrument, and reviewers
  met to reconcile substantive differences in
  interpretation. We calculated weighted pooled
  odds ratios based on an intention-to-treat
  analysis as well as subgroup analyses by quality
  score and study design.
• Results Stretching was not significantly
  associated with a reduction in total injuries (OR
  0.93, CI 0.78-1.11) and similar findings were
  seen in the subgroup analyses.
• Conclusion There is not sufficient evidence to
  endorse or discontinue routine stretching before
  or after exercise to prevent injury among
  competitive or recreational athletes. Further
  research, especially well-conducted randomized
  controlled trials, is urgently needed to
  determine the proper role of stretching in sports.

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Axler, CT. Med. Sci Sprt Exer., 29804, 1997.