The Scientific Principles of Strength Training

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The Scientific Principles of Strength Training

• Muscular Strength The amount of force a muscle
  can produce with a single maximal effort
• Mechanical Strength the maximum torque that can
  be generated about a joint

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Torque about the elbow joint

• Strength determined by
• Absolute force developed by muscle
• Distance from joint center to tendon insertion
• Angle of tendon insertion

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Shoulder joint torque as a function of arm
position
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(No Transcript)
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Structural organization of skeletal muscle
From Principles of Human Anatomy (7th edition),
1995 by Gerard J. Tortora, Fig 9.5, p 213
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From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.6, page 153
6-6
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From Skeletal Muscle Form and Function (2nd ed)
by MacIntosh, Gardiner, and McComas. Fig 1.4, p.
8.
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From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.5, page 152
6-5
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From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.3, page 150
6-3
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From Exercise Physiology Theory and Application
to Fitness and Performance (6th Edition) by Scott
K. Powers and Edward T. Howley. Fig 8.6 P. 147
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A motor unit single motor neuron and all the
muscle fibers it innervates
From Basic Biomechanics Instructors manual by
Susan Hall (2nd edition, 1995), Fig TM 31
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From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.7, page 154
6-7
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From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.8, page 154
6-8
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• Types of muscle fiber Fast twitch vs Slow Twitch
• Type I Type IIa Type IIb
• ST Oxidative FT Oxidative - FT
  Glycolytic
• (S0) Glycolytic (FOG)
  (FG)
• Contraction speed slow fast (2xI)
  fast (4xI)
• Time to peak force slow fast
  fast
• Fatigue rate slow inter.
  fast
• Fiber diam. small inter.
  large
• Aerobic capacity high inter.
  low
• Mitochondrial conc. high inter.
  low
• Anaerobic capacity low inter.
  High
• Sedentary people 50 slow/50 fast, whereas
  elite athletes may differ
• e.g., cross country skiers 75 slow 25 fast
• sprinters - 40 slow
  60 fast

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Factors affecting force Production

• Hypertrophy increase in the of myofibrils and
  myofilaments
• Hyperplasia increase in the number of fibers???

• 1. Cross-sectional area

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2. Rate Coding frequency of stimulation
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.9, page 155
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• 3. Spatial recruitment
• Increase of active motor units (MUs)
• Order of recruitment
• I ---gt IIa -----gt IIb
• Henneman's size principle MUs are recruited in
  order of their size, from small to large
• Relative contributions of rate coding and spatial
  recruitment.
• Small muscles - all MUs recruited at
  approximately 50 max. force thereafter, rate
  coding is responsible for force increase up to
  max
• Large muscles - all MUs recruited at
  approximately 80 max. force.

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4. Velocity of shortening Force inversely
related to shortening velocity
The force-velocity relationship for muscle
tissue When resistance (force) is negligible,
muscle contracts with maximal velocity.
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The force-velocity relationship for muscle
tissue As the load increases, concentric
contraction velocity slows to zero at isometric
maximum.
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Force-Velocity Relationship in different muscle
fiber types
Type II fiber
Type I fiber
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Effect of Temperature on Force-Velocity
relationship (22oC, 25oC, 31Co, and 37oC)
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Force -Velocity Relationship (Effect of
strength-Training)
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Force-velocity Relationship During Eccentric
Muscular Contractions
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Force/Velocity/Power Relationship
Force/velocity curve
Power/velocity curve
Force
Power
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From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.25, page 175
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Velocity
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Effect of Muscle Fiber Types on Power-Velocity
Relationship
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Consequences of the force-velocity relationship
for sports practice

• When training for sports that require power,
  train with the appropriate of 1 RM that will
  elicit the most power.
• 24 weeks of
• a). heavy weight-training b. Explosive
  strength training

From Science and Practice of Strength Training
(2nd edition) V.M. Zatsiorsky and W.J. Kraemer
(2006) Fig 2.19 P. 39)
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• Why do elite weight lifters start a barbell
  lift from the floor slowly?
• They try to accelerate maximally when the bar is
  at knee height. Two reasons
• 1. At this position, the highest forces can be
  generated as a result of body posture

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• 2. Because force decreases when velocity
  increases, barbell must approach the most favored
  position at a relatively low velocity to impart
  maximal force to the bar.

From Science and Practice of Strength Training
(2nd edition) V.M. Zatsiorsky and W.J. Kraemer
(2006) Fig 2.20 P. 40)
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Adaptations associated with strength training

• 1. Activates protein catabolism. This creates
  conditions for enhanced synthesis of contractile
  proteins during the rest period (break down,
  build up theory)

From R.L. Leiber (1992). Skeletal Muscle
Structure and Function. Fig 6.1, p. 262.
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• 2. Neural adaptations occur to improve
  intra-muscular and inter-muscular coordination.
• Intra-muscular coordination affects the ability
  to voluntarily activate individual fibers in a
  specific muscle
• Inter-muscular coordination affects the ability
  to activate many different muscles at the
  appropriate time

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• Intra-muscular coordination changes with
• training
• Untrained individuals find it difficult to
  recruit all their fast-twitch MUs. With training,
  an increase in MU activation occurs
• Strength training also trains the MUs to fire at
  the optimal firing rate to achieve tetany
• MUs might also become activated more
  synchronously during all out maximum effort

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• Consequently, maximal muscular force is achieved
  when
• 1. A maximal of both FT and ST motor units are
  recruited
• 2. Rate coding is optimal to produce a fused
  state of tetany
• 3. The MUs work synchronously over the short
  period of maximal effort.

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• Psychological factors are also of importance
• CNS either increases the flow of excitatory
  stimuli, decreases inhibitory stimuli, or both
• Consequently, an expansion of the recruitable
  motor neuron pool occurs and an increase in
  strength results
• Hidden strength potential of human muscle can
  also be demonstrated by electrostimulation
• Muscle strength deficit (MSD)
• (Force during electrostimulation-Maximal
  voluntary force) x 100
• Maximal voluntary force
• Typically falls between 5-35

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• Electrostimulation
• Possibility exists to induce hypertrophy through
  electrostimulation
• However, does not train the nervous system to
  recruit motor units
• Bilateral Deficit
• During maximal contractions, the sum of forces
  exerted by homonymous muscles unilaterally is
  typically larger than the sum of forces exerted
  by the same muscles bilaterally
• Bilateral training can eliminate this deficit, or
  even allow bilateral facilitation

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Other benefits of strength training

• Increase in resting metabolic rate
• Each additional pound of muscle tissue increases
• resting metabolism by 30 to 50 calories per
  day 10,950 to 18,250 calories a year 3-5 lb
  of fat
• Increase in bone mineral content and, therefore,
  bone density
• Increases the thickness and strength of the
  connective tissue structures crossing joints such
  as tendons and ligaments helps prevent injury
• Increased stores of ATP, Creatine Phosphate (CP),
  and glycogen
• Aids rehabilitation from injury
• Aging gracefully! Less falls in latter years
• Looking better, feeling better. Greater
  self-esteem

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Metabolic stress of resistance training

• Classed as only light to moderate in terms of
  energy expenditure per workout
• Standard weight-training does not improve
  endurance or produce significant cardiovascular
  benefits like aerobic type activity does
• Circuit-training increases metabolic stress

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Delayed onset of muscle soreness (DOMS)

• The intensity and the novelty of a workout
  influence how sore you become
• Lactate does not cause muscle soreness due to
• 1. Lactate returns to baseline within an hour of
  exercise
• 2. After exercise, lactate is in equal amounts
  within the muscle and the blood
• 3. DOMS is specific, not generalized
• Muscle soreness is due to the physiological
  response to muscle fiber and connective tissue
  damage (microtears)
• White blood cells enter the muscle tissue, clean
  up the debris of broken proteins, and then
  initiate the regeneration phase

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Muscle Soreness (continued)

• Edema (increase in fluid) to the area accompanies
  the above response
• The pressure from edema is thought to produce the
  sensation of soreness
• Also, metabolic by-products released from the
  macrophages may sensitize pain receptors
• Next stage is the proliferation of satellite
  cells - help form new myofibrils
• Eccentric contractions cause the greatest amount
  of soreness