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Chapter 4

KNES 351 Chapter Notes - Chapter 4: Pennate Muscle, Mechanical Advantage, Coccyx


Department
Kinesiology
Course Code
KNES 351
Professor
Andrew Galpin
Chapter
4

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Chapter 4. Biomechanics of Exercise
Objectives
Identify the major bones and muscles of the human body,
Differentiate among the various 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,
Recommend ways to minimize injury risk during resistance training, and
Analyze sport movements and design movement-oriented exercise
prescriptions
Anatomy: the study of the components of the musculoskeletal system.
Biomechanics: the study of the interaction between these components to
create movement.
Musculoskeletal System
Consists of joints, muscles, bones, and tendons.
The configuration of these structures determines the characteristic of the
movement.
Skeleton
Muscles rotate about joints and transmit force; they pull bone (which act as
levers) to produce force.
There are 206 bones in the body but the number can vary.
Axial skeleton: skull, vertebral column, ribs, sternum.
Appendicular skeleton: shoulder girdle, bones of the arms, wrists, and
hands, pelvic girdle, legs, ankles, feet.
Joints: junctions at which bones meet or articulate.
o Fibrous joints (such as sutures) permit no movement.
o Cartilaginous joints: allow limited movement.
o Synovial joints: allow the most amount of movement.
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2
Low friction and large range of motion; sports movements are
performed by these joints.
Articulating bone ends are covered with hyaline cartilage while
the entire joint is enclosed in a capsule filled with synovial
fluid.
Joints can be categorized by the number of directions about which rotation
can occur.
o Uniaxial joints: single axis.
o Biaxial joints: two perpendicular axes.
o Multiaxial joints: all three perpendicular axes that define space.
Vertebral column made up of flexible discs that allow for some movement
to occur.
o 7 C, 12 T, 5 L.
o 5 sacral vertebrae (fused together); 3-5 coccygeal vertebrae.
Skeletal Musculature
Origin: proximal attachment.
o The more stationary structure.
Insertion: distal attachment.
Muscles are attached to bones in different ways:
o Fleshy attachments: muscle is directly fixed to the bone.
o Fibrous attachments (tendons): muscle sheath and bone are
continuous with each other.
Muscle that most directly brings about the movement is agonist; the
muscle that slows down movement is called the antagonist.
o Antagonist assists in stabilization and prevents uncontrollable
acceleration during force production.
o Synergist: a muscle that indirectly assists in the force production of a
movement.
Levers of the Musculoskeletal System
Mechanical advantage: The ratio of the moment arm through which an
applied force acts to that through which a resistive force acts (figure 4.3).
For there to be a state of equilibrium between the applied and resistive
torques, the product of the muscle force and the moment arm through
which it acts must equal the product of the resistive force and the moment
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3
arm through which it acts. Therefore, a mechanical advantage greater than
1.0 allows the applied (muscle) force to be less than the resistive force to
produce an equal amount of torque. A mechanical advantage of less than
1.0 is a disadvantage in the common sense of the term.
Levers
o First class lever: the muscle force and resistive force act oppositely
across the fulcrum.
o Second class lever: muscle force and resistive force act on the same
side as the fulcrum; the moment arm of the muscle is longer so there
is a mechanical advantage; less force is required to overcome the
resistive force.
o Third class lever: muscle force and resistive force act on the same
side as the fulcrum; the moment arm of the muscle is shorter so
there is a mechanical advantage; more force is required to overcome
the resistive force.
Most muscles rotate at a mechanical disadvantage (efficiency of less than
1.0).
Classification of levers is dependent upon the [arbitrary] placement of the
fulcrum.
o Mechanical advantages change continuously.
Variations in Tendon Insertion
Variation in structure can have profound effects on movement production.
o If tendons are inserted farther from joint center, then force
production should be increased because the moment arm is longer
and thus more capable of producing torque.
o However, this configuration leads to a loss in maximum speed
because the muscle has to contract more at a given range of motion.
Human Strength and Power
There are several measurements of strength: concentric (traditional),
isometric, and isokinetic.
All sports involve acceleration, which is a necessary component in force
production.
Under this definition, strength can be defined as the maximal force that a
muscle can generate at a specified/given velocity.
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