Biomechanics of Resistance Exercise

Document Sample
Biomechanics of Resistance Exercise Powered By Docstoc
					chapter
Biomechanics of Resistance Exercise

  4
          Biomechanics
          of Resistance
          Exercise



          Everett Harman, PhD, CSCS, NSCA-CPT
            Chapter Objectives

• Identify the major bones and muscles of the
  human body.
• Differentiate among the types of levers of the
  musculoskeletal system.
• Calculate linear and rotational work and power.
• Describe the factors contributing to human
  strength and power.
• Evaluate resistive force and power patterns of
  exercise devices.
                                           (continued)
   Chapter Objectives (continued)

• Recommend ways to minimize injury risk during
  resistance training.
• Analyze sport movements and design movement-
  oriented exercise prescriptions.
                Section Outline

• Musculoskeletal System
  –   Skeleton
  –   Skeletal Musculature
  –   Levers of the Musculoskeletal System
  –   Variations in Tendon Insertion
  –   Anatomical Planes of the Human Body
               Key Terms

• anatomy: The study of components that make
  up the musculoskeletal “machine.”
• biomechanics: The mechanisms through
  which these components interact to create
  movement.
         Musculoskeletal System

• Skeleton
  – Muscles function by pulling against bones that rotate about
    joints and transmit force through the skin to the environment.
  – The skeleton can be divided into the axial skeleton and the
    appendicular skeleton.
• Skeletal Musculature
  – A system of muscles enables the skeleton to move.
  – Origin = proximal (toward the center of the body) attachment
  – Insertion = distal (away from the center of the body) attach-
    ment
    Human Skeletal Musculature

• Figure 4.1 (next slide)
  – (a) Front view of adult male human skeletal
    musculature
  – (b) Rear view of adult male human skeletal
    musculature
Figure 4.1
                 Key Terms

• agonist: The muscle most directly involved in
  bringing about a movement; also called the
  prime mover.
• antagonist: A muscle that can slow down or
  stop the movement.
Figure 4.5
Figure 4.7
Figure 4.8
        Musculoskeletal System

• Variations in Tendon Insertion
  – tendon insertion: The points at which tendons are
    attached to bone.
  – Tendon insertion farther from the joint center results
    in the ability to lift heavier weights.
     • This arrangement results in a loss of maximum speed.
     • This arrangement reduces the muscle’s force capability
       during faster movements.
 Tendon Insertion and Joint Angle

• Figure 4.9 (next slide)
  – The slide shows changes in joint angle with equal
    increments of muscle shortening when the tendon is
    inserted (a) closer to and (b) farther from the joint
    center.
  – Configuration (b) has a larger moment arm and thus
    greater torque for a given muscle force, but less
    rotation per unit of muscle contraction and thus
    slower movement speed.
                                             Figure 4.9




Reprinted, by permission, from Gowitzke and Milner, 1988.
       Musculoskeletal System

• Anatomical Planes of the Human Body
  – The body is erect, the arms are down at the sides,
    and the palms face forward.
  – The sagittal plane slices the body into left-right
    sections.
  – The frontal plane slices the body into front-back
    sections.
  – The transverse plane slices the body into upper-
    lower sections.
Figure 4.10
                 Section Outline

• Human Strength and Power
  – Basic Definitions
  – Biomechanical Factors in Human Strength
     •   Neural Control
     •   Muscle Cross-Sectional Area
     •   Arrangement of Muscle Fibers
     •   Muscle Length
     •   Joint Angle
     •   Muscle Contraction Velocity
     •   Joint Angular Velocity
     •   Strength-to-Mass Ratio
     •   Body Size
     Human Strength and Power

• Basic Definitions
  – strength: The capacity to exert force at any given
    speed.
  – power: The mathematical product of force and
    velocity at whatever speed.
     Human Strength and Power

• Biomechanical Factors in Human Strength
  – Neural Control
     • Muscle force is greater when: (a) more motor units are
       involved in a contraction, (b) the motor units are greater
       in size, or (c) the rate of firing is faster.
  – Muscle Cross-Sectional Area
     • The force a muscle can exert is related to its cross-
       sectional area rather than to its volume.
  – Arrangement of Muscle Fibers
     • Variation exists in the arrangement and alignment of
       sarcomeres in relation to the long axis of the muscle.
     Human Strength and Power

• Biomechanical Factors in Human Strength
  – Muscle Length
     • At resting length: actin and myosin filaments lie next to
       each other; maximal number of potential cross-bridge sites
       are available; the muscle can generate the greatest force.
     • When stretched: a smaller proportion of the actin and
       myosin filaments lie next to each other; fewer potential
       cross-bridge sites are available; the muscle cannot
       generate as much force.
     • When contracted: the actin filaments overlap; the number
       of cross-bridge sites is reduced; there is decreased force
       generation capability.
       Muscle Length and Actin
        and Myosin Interaction

• Figure 4.12 (next slide)
  – The slide shows the interaction between actin and
    myosin filaments when the muscle is at its resting
    length and when it is contracted or stretched.
  – Muscle force capability is greatest when the muscle
    is at its resting length because of increased
    opportunity for actin-myosin cross-bridges.
Figure 4.12
     Human Strength and Power

• Biomechanical Factors in Human Strength
  – Joint Angle
     • Amount of torque depends on force versus muscle length,
       leverage, type of exercise, the body joint in question, the
       muscles used at that joint, and the speed of contraction.
  – Muscle Contraction Velocity
     • Nonlinear, but in general, the force capability of muscle
       declines as the velocity of contraction increases.
  – Joint Angular Velocity
     • There are three types of muscle action.
                   Key Term

• concentric muscle action: A muscle action in
  which the muscle shortens because the con-
  tractile force is greater than the resistive force.
  The forces generated within the muscle and
  acting to shorten it are greater than the external
  forces acting at its tendons to stretch it.
                   Key Term

• eccentric muscle action: A muscle action in
  which the muscle lengthens because the
  contractile force is less than the resistive force.
  The forces generated within the muscle and
  acting to shorten it are less than the external
  forces acting at its tendons to stretch it.
                   Key Term

• isometric muscle action: A muscle action in
  which the muscle length does not change
  because the contractile force is equal to the
  resistive force. The forces generated within the
  muscle and acting to shorten it are equal to the
  external forces acting at its tendons to stretch it.
     Human Strength and Power

• Biomechanical Factors in Human Strength
  – Strength-to-Mass Ratio
     • In sprinting and jumping, the ratio directly reflects an
       athlete’s ability to accelerate his or her body.
     • In sports involving weight classification, the ratio helps
       determine when strength is highest relative to that of other
       athletes in the weight class.
     Human Strength and Power

• Biomechanical Factors in Human Strength
  – Body Size
     • As body size increases, body mass increases more rapidly
       than does muscle strength.
     • Given constant body proportions, the smaller athlete has a
       higher strength-to-mass ratio than does the larger athlete.
Cam-Based Weight-Stack Machines

• Figure 4.14 (next slide)
  – In cam-based weight-stack machines, the moment
    arm (M) of the weight stack (horizontal distance from
    the chain to the cam pivot point) varies during the
    exercise movement.
  – When the cam is rotated in the direction shown from
    position 1 to position 2, the moment arm of the
    weights, and thus the resistive torque, increases.
Figure 4.14
                Section Outline

• Joint Biomechanics: Concerns in
  Resistance Training
  – Back
     • Back Injury
     • Intra-Abdominal Pressure and Lifting Belts
  – Shoulders
  – Knees
      Joint Biomechanics:
 Concerns in Resistance Training

• Back
  – Back Injury
     • The lower back is particularly vulnerable.
     • Resistance training exercises should generally be
       performed with the lower back in a moderately arched
       position.
  – Intra-Abdominal Pressure and Lifting Belts
     • The “fluid ball” aids in supporting the vertebral column
       during resistance training.
     • Weightlifting belts are probably effective in improving
       safety. Follow conservative recommendations.
Figure 4.15
                 Key Term

• Valsalva maneuver: The glottis is closed, thus
  keeping air from escaping the lungs, and the
  muscles of the abdomen and rib cage contract,
  creating rigid compartments of liquid in the
  lower torso and air in the upper torso.
       Joint Biomechanics:
  Concerns in Resistance Training
• Shoulders
  – The shoulder is prone to injury during weight training because
    of its structure and the forces to which it is subjected.
  – Warm up with relatively light weights.
  – Follow a program that exercises the shoulders in a balanced
    way.
  – Exercise at a controlled speed.
• Knees
  – The knee is prone to injury because of its location between two
    long levers.
  – Minimize the use of wraps.
      Joint Biomechanics:
 Concerns in Resistance Training
• How Can Athletes Reduce the Risk of
  Resistance Training Injuries?
  – Perform one or more warm-up sets with relatively
    light weights, particularly for exercises that involve
    extensive use of the shoulder or knee.
  – Perform basic exercises through a full ROM.
  – Use relatively light weights when introducing new
    exercises or resuming training after a layoff of two or
    more weeks.
  – Do not ignore pain in or around the joints.
                                                 (continued)
       Joint Biomechanics:
  Concerns in Resistance Training
• How Can Athletes Reduce the Risk of
  Resistance Training Injuries? (continued)
  – Never attempt lifting maximal loads without proper
    preparation, which includes technique instruction in
    the exercise movement and practice with lighter
    weights.
  – Performing several variations of an exercise results
    in more complete muscle development and joint
    stability.
  – Take care when incorporating plyometric drills into a
    training program.
           Section Outline

• Movement Analysis and Exercise
  Prescription
        Major Body Movements

• Figure 4.16 (next two slides)
  – Planes of movement are relative to the body in the
    anatomical position unless otherwise stated.
  – Common exercises that provide resistance to the
    movements and related sport activities are listed.
                                         Figure 4.16




Reprinted, by permission, from Harman, Johnson, and Frykman, 1992.
                       Figure 4.16 (continued)




Reprinted, by permission, from Harman, Johnson, and Frykman, 1992.
                Key Point

• Specificity is a major consideration when
  one is designing an exercise program to
  improve performance in a particular sport
  activity. The sport movement must be
  analyzed qualitatively or quantitatively to
  determine the specific joint movements that
  contribute to the whole-body movement.
  Exercises that use similar joint movements
  are then emphasized in the resistance
  training program.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:6
posted:12/15/2011
language:
pages:43