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The Scientific Principles of Strength Training

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Title: The Scientific Principles of Strength Training


1
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

2
Torque about the elbow joint
  • Strength determined by
  • Absolute force developed by muscle
  • Distance from joint center to tendon insertion
  • Angle of tendon insertion

3
Shoulder joint torque as a function of arm
position
4
(No Transcript)
5
Structural organization of skeletal muscle
From Principles of Human Anatomy (7th edition),
1995 by Gerard J. Tortora, Fig 9.5, p 213
6
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.6, page 153
6-6
7
From Skeletal Muscle Form and Function (2nd ed)
by MacIntosh, Gardiner, and McComas. Fig 1.4, p.
8.
8
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.5, page 152
6-5
9
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.3, page 150
6-3
10
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
11
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
12
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.7, page 154
6-7
13
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.8, page 154
6-8
14
  • 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

15
Factors affecting force Production
  • Hypertrophy increase in the of myofibrils and
    myofilaments
  • Hyperplasia increase in the number of fibers???
  • 1. Cross-sectional area

16
2. Rate Coding frequency of stimulation
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.9, page 155
17
  • 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.

18
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.
19
The force-velocity relationship for muscle
tissue As the load increases, concentric
contraction velocity slows to zero at isometric
maximum.
20
Force-Velocity Relationship in different muscle
fiber types
Type II fiber
Type I fiber
21
Effect of Temperature on Force-Velocity
relationship (22oC, 25oC, 31Co, and 37oC)
22
Force -Velocity Relationship (Effect of
strength-Training)
23
Force-velocity Relationship During Eccentric
Muscular Contractions
24
Force/Velocity/Power Relationship
Force/velocity curve
Power/velocity curve
Force
Power
30
From Basic Biomechanics by Susan Hall (3rd
edition), Fig 6.25, page 175
30
Velocity
25
Effect of Muscle Fiber Types on Power-Velocity
Relationship
26
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)
27
  • 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

28
  • 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)
29
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.
30
  • 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

31
  • 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

32
  • 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.

33
  • 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

34
  • 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

35
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

36
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

37
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

38
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
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