Strength Training

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Strength Training

• Patricia A. Deuster, PhD, MPHUniformed Services
  University

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Outline of Presentation

• Define strength training
• Factors affecting force generation
• Development of muscle strength
• Muscular power and endurance
• Approaches to strength training
• Benefits of strength training
• Designing a strength training program.

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Objectives

• Identify strength training terms
• Discuss trends in the prevalence of strength
  training
• Discuss factors that determine muscle force
  development
• Identify and differentiate skeletal muscle fiber
  types
• Discuss strength training terms and how to
  develop a strength training program
• Describe benefits of strength training.

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Strength Training Terms

• Progressive Overload
• Specificity and Variation
• Periodization
• Loading
• Training Volume, Impulse
• Exercise Selection and Order
• Rest Periods and Frequency
• Muscle Action and Velocity of muscle action

• Adaptation
• Muscular Strength
• Muscular Hypertrophy
• Muscular Power
• Muscular Endurance
• Motor Performance

Kraemer et al American College of Sports
Medicine position stand. Progression models in
resistance training for healthy adults. Med Sci
Sports Exerc. 2002 Feb34(2)364-80.
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Healthy People 2010 Objective and Strength
Training

• Increase to 30 the proportion of adults who
  perform physical activities that enhance and
  maintain muscular strength and endurance on gt 2
  days per week
• Also recommended by the American College of
  Sports Medicine.

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Prevalence of Strength Training by Gender
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Prevalence of Strength Training by Ethnicity
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Factors Affecting Muscular Force Generation

• Muscle Architecture
• Muscle Mechanics
• Length-Tension Relationship
• Muscle Fiber Types
• Force-Velocity Relationship
• Electromechanical Delay

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Muscle Architecture

• Long axis of muscle determines arrangement of
  muscle fibers
• Reflects muscle force and power
• Two basic types
• Fusiform spindle shaped
• Pennate fan-shaped

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Muscle Fiber Architecture
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Pennation Effects on Force and Fiber Packing

• Pennation allows for packing a more fibers into a
  smaller cross-sectional area than parallel
  fibers.
• ? surface pennation angle

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Fusiform Fiber Arrangement
Fa force of contraction of muscle fiber
parallel to long axis of muscle SFa sum of all
muscle fiber contractions parallel to long axis
of muscle
Fa
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Pennate Fiber Arrangement
Fa force of contraction of muscle fiber
parallel to long axis of muscle Fm force of
contraction of muscle fiber ? pennation
angle Fa (cos ?)(Fm) SFa sum of all muscle
fiber contractions parallel to long axis of muscle
Fa
Fm
?
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Muscle Mechanics

• Active Force through contractile elements actin
  and myosin mechanism
• Passive Force through elastic elements
• Series elastic elements (tendons) smooth out
  force of contraction and reduce effects of
  external forces from overloads
• Parallel elastic elements (fascia) absorb energy
  input externally if muscle is stretched beyond
  normal "resting" length.

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Muscle Mechanics
PE Parallel elastic component SE Series
elastic component CE Contractile element
Fibers in series Force production modest, but
large range of shortening. Fibers in
parallel Force production high, but minimal range
of shortening.

• The range of motion and amount of force a muscle
  can generate is largely determined by the
  arrangement of the muscle fibers

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Length-Tension Relationship

• Force generation optimized when muscle is
  slightly stretched.
• Due to contribution of elastic components of
  muscle (primarily the SEC)

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Human Muscle Fiber Types
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Human Muscle Fiber Types
Characteristics Names ST FTa
FTd/x SO FOG FG Fibers/Motor
Neuron 10-180 300-800 300-800 Motor Neuron
Size Small Large Large Nerve Conduction
Velocity Slow Fast Fast Contraction Speed
(ms) 110 50 50 Type of Myosin ATPase Slow Fast F
ast SR Development Low High High Motor Unit
Force Low High High
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Comparison of Maximal Shortening Velocities
Between Fiber Types
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Force and Types of Muscle Contractions
Concentric
Eccentric
Isometric
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Isotonic Contractions

• Muscle changes length (changing angle of joint)
  and moves a load.
• Two types of isotonic contractions
• Concentric Muscle shortens as it contracts
• Eccentric Muscle lengthens as it contracts

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Isometric Contractions

• Tension increases without changes in length
• Occurs if the load is greater than the tension
  the muscle is able to develop

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Force-Velocity Relationship

• Maximal force developed by muscle is governed by
  its shortening or lengthening velocity - holds
  true for all muscle types

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Force Velocity Relationships

• Concentric CON
• Ability to develop force is greater at slower
  contraction velocities - allows greater time for
  cross-bridges to generate tension

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Force-Velocity Relationship

• Eccentric ECC
• Greater force with increasing velocity/
  acceleration, due to lower metabolic cost,
  greater mechanical efficiency and greater
  contribution from series elastic components.

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Force-Velocity Relationship
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Electromechanical Delay

• Time between arrival of neural stimulus and
  tension development by muscle
• Varies among muscles (20-100 msec)
• Short EMDs produced by muscles with high
  percentage of FT fibers
• Not affected by muscle length, contraction type,
  contraction velocity, or fatigue

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Electromechanical Delay
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Development of Muscle Strength

• Maturation
• Training

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Maturation and Strength
Factors contributing to muscle strength during
maturation
100 Adult potential
Lean body mass
Theoretical fiber type differentiation
Testosterone
Neural myelination development
Birth Puberty Adult
Strength primarily via motor patterns
Consolidation of strength factors
Optimal strength potential
Kraemer, 1989
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Adaptations to Strength Training

• Physiological Adaptations
• ? muscle fiber size and strength
• ? connective tissue density and bone integrity.
• Muscle fiber type conversion?
• Neural Adaptations
• ? recruitment of motor units
• ? in firing rate of motor neurons
• Improved synchronization in motor neuron firing
• Counteraction of autogenic inhibition to allow
  greater force production.

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Skeletal Muscle Adaptations

• Muscle Fiber Size
• Muscle Fiber Type Conversion
• Muscular Strength

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Muscle Fiber Hypertrophy

• Increase in numbers of myofibrils and actin and
  myosin filaments
• Allows more cross-bridges.
• Increases in muscle protein synthesis during
  post-exercise period.
• Testosterone plays a role in promoting muscle
  growth.
• High intensity training may promote greater fiber
  hypertrophy than low intensity training.

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Muscle Fiber Hyperplasia

• Muscle fibers may split in half with intense
  weight training.
• Each half may then increases to size of parent
  fiber.
• Satellite cells may also be involved in skeletal
  muscle fiber generation.
• Clearly shown in animal models, but in only a few
  human studies.

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Process of Strength Gains

• Early strength gains influenced by neural factors.

• Long-term strength gains due to muscle
  hypertrophy.

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Mechanisms of Strength Training Adaptations

• Mechanical stimuli
• CON-only training equally effective as ECC,
  despite mechanical advantage of ECC (greater
  forces, muscle damage, etc)
• Metabolic Stimuli
• Greater metabolic costs with CON
• Build-up of metabolic by-products may enhance
  release of anabolic hormones and lead to greater
  motor unit activation.

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Muscular Power

• Power Work/Time
• (Force X Distance)/Time
• Force X Velocity
• Maximal power occurs at
• 1/3 max velocity
• 1/3 max concentric force
• Affected by muscular strength and movement speed
• Main determinant of performance for throwing,
  jumping, changing direction, and striking
  activities.

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Force-Power Relationship

• Power generated is greater in muscle with a high
  of fast-twitch fibers at any given velocity of
  movement
• Peak power increases with velocity up to movement
  speeds of 200-300ºsec-1
• Force decreases with increasing movement speed
  beyond this velocity

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Force-Power Relationship
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Muscle Load and Shortening Velocity

• Max velocity at minimum load
• Max load at velocity 0

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• Power (force x velocity)
• Power 0 at 0 load and max load
• Maximal power of muscle occurs at 1/3rd max load,
  or where Velocity X Load is greatest.

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Velocity of Contraction (cm/s)
10
0
max
0.33
0.66
Load opposing contraction
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Muscular Endurance

• The ability to exert tension over a period of
  time.
• Constant gymnast in iron cross
• Varying rowing, running, cycling
• Length of time dramatically affected by force and
  speed requirements of activity.
• Training involves many repetitions with light
  resistance.

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Approaches to Strength Training

• Static (isometric) actions
• Dynamic actions
• Free weights
• Gravity dependent
• Variable resistance
• Isokinetic actions
• Plyometrics
• Other
• Neuromuscular electrical stimulation

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Free Weights

• Gravity dependent
• Resistance pattern constant or variable
• Concentric and eccentric action of same muscles
  antagonistic muscles not utilized
• Momentum may be factor in resistance pattern

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Gravity Dependent Machines

• Universal Gym
• Resistance moves upward
• Round pulleys changes direction of resistance
• Constant resistance

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Variable Resistance Machines

• Nautilus
• Cam design creates variable resistance
• Designed to mimic strength curve

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Isokinetic Devices

• Biodex, Cybex, Orthotron, and hydraulic equipment
• Accommodating resistance
• Constant velocity

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Plyometrics

• Used to develop jumping, sprinting and explosive
  power
• Muscle is contracted eccentrically then
  immediately concentrically (muscle is lengthened
  before it is contracted)
• Should not be done more than 2x/wk
• Requires 100 effort for all movements
• Need adequate rest time between exercises to
  recover 1 to 5 workrest ratio.

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Other Devices

• The body pushups, sit-ups, pull-ups
• Pushup variations
• Sit-ups, curl-ups - changing resistance
• Pull-ups pronated vs. supinated grip

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Neuromuscular Electrical Stimulation

• Characterized by low volt stimulation targeted to
  stimulate motor nerves to cause a muscle
  contraction.
• Brain sends a special signal via a nerve impulse
  to muscle "motor point" causing muscle to
  contract and exercise just as if it had received
  a signal from the brain.
• TENS is designed to stimulate sensing nerve
  endings to help decrease pain. 

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Strength Training Benefits

• Reduces
• of injuries
• Severity of injuries
• Rehabilitation time
• Increases and Maintains
• Strength and power
• Endurance and stamina
• Lean body mass
• Develops
• Mental focus toughness

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Designing Strength Training Programs

• Identify goals, depending on sport and equipment
  available
• Carry out strength testing to select appropriate
  resistance levels
• Repetition Maximum or RM - Maximum amount of
  weight lifted for a given number of reps
• 1RM amount of weight that can be lifted only
  one time.

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Determining a 1RM

• Warm up for 10 minutes then select weight light
  enough for gt 10 reps
• Perform 12 - 15 reps, then rest 2 minutes
• Increase weight 2 - 10, perform 10 - 12 reps,
  then rest 3 minutes.
• Increase weight 2 - 10, perform 6 - 8 reps then
  rest for 3 minutes.
• Increase weight 2 - 10, perform 5 reps - should
  be close to 5RM
• Multiply 5RM weight by 1.15 to get 1RM.

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Key Training Principles
Overload
Specificity
Progression
Individualism
Adaptation
Maintenance
Periodization
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Periodization

• Training technique that involves altering
  training variables over a specific period to
  achieve well-defined gains in strength,
  endurance, and overall performance.
• Cycle of phases activation (getting ready for
  new activity), strength development, muscular
  endurance development, and active recovery.

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Acute Program Variables
Muscle Action
Rest Periods
Load and Volume
Repetition Velocity
Exercise Selection and Order
Frequency
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Muscle Action

• Dynamic repetitions of concentric (CON) and
  eccentric (ECC) actions
• Isometric actions serve stabilizing role
• Concentric actions elicit greater growth hormone
  response
• Training should include both CON and ECC.

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Loading and Volume

• Load amount of weight - key variable
• Determined by RM or of 1RM
• Increase by 2-10 when can perform load for 1-2
  reps over desired reps
• Maximal strength gained with 12RM in untrained
  and 8RM in trained
• Volume total work performed

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Number of Sets

• Multiple set programs and periodized multiple set
  programs are superior to single set programs over
  both short and long term periods for strength
• 3 sets better than 6 and 12 sets
• Altering frequency, intensity and volume best
  strategy to improve strength.

Galvao DA et al. J Strength Cond Res. 2004
Aug18(3)660-667.
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Volume of Training

• Sets x Repetitions x Resistance

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Impulse
Product of force applied and time during which it
acts Impulse Force x Time of application
Impulse
Force
Time
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Exercise Selection and Order

• Single Joint (leg extension, biceps curl) - less
  risk because requires less skill
• Multiple Joint more neurally demanding and more
  effective for overall strength
• Order - from large to small muscle mass/groups

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Rest Periods

• Dependent on
• Training goal
• Relative load lifted
• Status of individual
• Primary determinant of intensity
• Affects metabolic and hormonal demands
• Determines amount of ATP-CR resynthesis

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Repetition Velocity

• Not adequate research but
• Gold Standard 214 or 2 s CON 1 s pause 4
  s ECC
• Slow 24 ( good for novices)
• Super Slow 105
• Moderate 22
• Fast 11

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Frequency

• Function of type of training session, training
  status, and recovery of person
• Typical 2 -3 d/wk to allow for recuperation
• Maintenance 2 d/wk
• Competitive Lifters 5 - 7 d/wk

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Specific Training Outcomes
Muscle Endurance
Muscle Hypertrophy
Maximal Strength
Power
ECCCON 1-3 Sets 15-20RM 30-60s rest 101 2-3x/wk
ECCISOCON 4-6 sets 8-15RM 1-2m
rest 212 3-5d/wk
ECCISOCON 3-5 sets 3-8RM 3-5m rest 111 3-5d/wk
ECCCON 3-5 sets 1-3RM 5-8m rest Explosive 4-6d/wk
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Periodization Plan
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Approximate Intensity Levels Relative to a 1RM
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Optimal Strength Gains

• Maximal strength gains elicited with training
  intensity of 85 of 1RM (2 - 5 reps), 2 d/wk,
  with 8 sets per muscle group.
• Peterson MD et al. J Strength Cond Res. 2004
  May18(2)377-382.

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Optimal Power Gains

• Optimal load for maximal power gains depends on
  nature of exercise (single versus multiple joint
  exercises) and experience of athlete
• Untrained load 30-45 of 1RM
• Trained load 40 - 70 of 1 RM
• Explosive training best
• Periodization important

Kawamori N et al. J Strength Cond Res.
200418(3)675-84.
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Eccentric Loading

• Supra maximal loading to optimize force
  production
• E.g. loads set at 100, 130 and 150 of 1RM
• May be useful for recruiting high threshold motor
  units.

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Safety of Strength Training

• Relative Safety of Weightlifting and Weight
  Training. Hamill 1994.
• Injury rates were 0.0012 per 100 hours of
  participation compared to 0.03 for basketball,
  0.1 for football, and 0.03 for all other
  athletics.
• Regular participation in broad-based training
  that includes strength training can significantly
  lower sports-related injury rates and time for
  rehab of adolescents. Faifenbaum 2004.

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Physical Performance and Injury Prevention Model

• Primary Exercises
• 1. Leg Press or Parallel Squat
• 2. Bench Press or Incline Bench
• 3. Lat Pulldown or Low Pull
• 4. Shoulder Press or Upright Row
• Secondary Exercises
• 5. Leg Curl and Leg Extension
• 6. Biceps Curl and Triceps Extension
• 7. Low Back Extension and Abs Crunch
• 8. Grip/Forearm and Calves

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Contribution of Strength to Performance of Tasks
Size Strength Fitness
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ACSM Position Stand

• To develop and maintain cardiorespiratory and
  muscular fitness, and flexibility in healthy
  adults
• 812 repetitions for 810 exercises, including
  one exercise for all major muscle groups
• 1015 repetitions for older and more frail
  persons.

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Summary Strength Training

• Is a physiologic stimulus with multiple actions
• Is complex and requires administrative and
  physiologic planning
• Confers benefits to young and old, weak and
  strong
• Is safe when entered into with clearly defined
  goals
• Requires an understanding to be effective.

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Questions ?
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