Chapter 3
Basic Biomechanical Factors & Concepts
Types of machines found in the body
· Musculoskeletal system may be thought of as a series
of simple machines
Types of machines found in the body
· Machines function in four ways
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Types of machines found in the body
· Musculoskeletel system arrangement provides for 3 types
of machines in producing movement
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Levers
· Humans moves through a system of levers
· Levers cannot be changed, but they can be utilized more
efficiently
lever - ________________________________________________________
axis - _________________________________________________________
Levers
· Levers rotate about an axis as a result of force
(effort, E) being applied to cause its movement against
a resistance or weight
· In the body
bones represent the bars
joints are the axes
muscles contract to apply force
Levers
· Resistance can vary from maximal to minimal
May be only the bones or weight of body segment
· All lever systems have each of these three components
in one of three possible arrangements
Levers
· Three points determine type of lever & for which
kind of motion it is best suited
Axis (A)- fulcrum - ----____________________________________
Point (F) __________________________________________
Point (R) __________________________________________
Levers
· 1st class lever ______________________________________
· 2nd class lever ______________________________________
· 3rd class lever ______________________________________
Levers
First-class Levers
· Produce balanced movements when axis is midway between
force & resistance (e.g., seesaw)
· Produce speed & range of motion when axis is close
to force, (triceps in elbow extension)
· Produce force motion when axis is close to resistance
(crowbar)
First-class Levers
· Head balanced on neck in flexing/extending
· Agonist & antagonist muscle groups are contracting
simultaneously on either side of a joint axis
agonist produces force while antagonist supplies resistance
First-class Levers
· Elbow extension in triceps applying force to olecranon
(F) in extending the non-supported forearm (R) at
the elbow (A)
First-class Levers
· Force is applied where muscle inserts in bone, not in
belly of muscle
Ex. in elbow extension with shoulder fully flexed &
arm beside the ear, the triceps applies force to the olecranon
of ulna behind the axis of elbow joint
As the applied force exceeds the amount of forearm resistance,
the elbow extends
First-class Levers
Change example by placing the hand on the floor (as in a
push-up) to push the body away from the floor, the same muscle
action at this joint now changes the lever to 2nd class due to
the axis being at the hand and the resistance is body weight at
the elbow joint
Second-class Levers
· Produces force movements, since a large resistance can
be moved by a relatively small force
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Second-class Levers
Plantar flexion of foot to raise the body up on the toes
where ball (A) of the foot serves as the axis as ankle plantar
flexors apply force to the calcaneus (F) to lift the resistance
of the body at the tibial articulation (R) with the foot
· Relatively few 2nd class levers in body
Third-class Levers
· Produce speed & range-of-motion movements
· ______________________________________
· Requires a great deal of force to move even a small resistance
______________________________________
Third-class Levers
Biceps brachii in elbow flexion
Using the elbow joint (A) as the axis, the biceps brachii applies
force at its insertion on radial tuberosity (F) to rotate forearm
up, with its center of gravity (R) serving as the point of resistance
application
Third-class Levers
· Brachialis - true 3rd class leverage
pulls on ulna just below elbow
pull is direct & true since ulna cannot rotate
· Biceps brachii supinates forearm as it flexes so its
3rd class leverage applies to flexion only
· Other examples
hamstrings contracting to flex leg at knee while in a standing
position
using iliopsoas to flex thigh at hip
Factors in use of anatomical levers
· Anatomical leverage system can be used to gain a mechanical
advantage
· Improve simple or complex physical movements
· Some habitually use human levers properly
· Some develop habits of improperly use human levers
Laws of motion and physical activities
· Body motion is ______________________________________
· Motion cannot occur ______________________________________
· Muscular system is ______________________________________
· Two types of motion
Laws of motion and physical activities
· Linear motion (_________________________) - motion along
a line
rectilinear motion - _________________________________
curvilinear motion - _________________________________
Linear displacement - ______________________________________________________
· Angular motion (rotary motion) - rotation around an axis
In the body, the axis of rotation is provided by the various
joints
· Angular displacement - _________________________________
· Linear & angular are related
angular motion of the joints produces the linear motion
of walking
Laws of motion and physical activities
· Sports ex. - cumulative angular motion of the joints
imparts linear motion to a thrown object (ball, shot) or to an
object struck with an instrument (bat, racket)
· Displacement - the actual distance that the
object has been displaced from its original point of reference
Laws of motion and physical activities
· Distance - actual sum length of measurement traveled
object may have traveled a distance of 10 meters along a
linear path in two or more directions but only be displaced from
its original reference point by 6 meters
· Newton's laws of motion have many applications to physical
education activities and sports
Law of Inertia
· ____________________________________________________________________
· Muscles produce force to start, stop, accelerate, decelerate & change the direction of motion
Law of Inertia
· Inertia - ______________________________
In human movement, inertia refers to resistance to acceleration
or deceleration
tendency for the current state of motion to be maintained,
regardless of whether the body segment is moving at a particular
velocity or is motionless
the reluctance to change status; only force can change status
Law of Inertia
· _____________________________________________
_____________________________________________
· Examples
Sprinter in starting blocks must apply considerable force
to overcome his resting inertia
Runner on an indoor track must apply considerable force
to overcome moving inertia & stop before hitting the wall
Thrown or struck balls require force to stop them
Law of Inertia
· ----____________is required to change inertia
Any activity carried out at a steady pace in a consistent
direction will conserve energy
Any irregularly paced or directed activity will be very
costly to energy reserves
Ex. handball & basketball are so much more fatiguing
than jogging or dancing
Law of Acceleration
· ____________________________________________________
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Law of Acceleration
· Acceleration - ___________________________
To attain speed in moving the body, a strong muscular force
is generally necessary
· Mass - _________________________________
affects the speed & acceleration in physical movements
Law of Acceleration
· A much greater force is required from the muscles to
accelerate a 230-pound man than than to accelerate a 130-pound
man to the same running speed
· A baseball maybe accelerated faster than a shot because
of the difference in weight
· The force required to run at half speed is less than
the force required to run at top speed
· To impart speed to a ball or an object, the body part
holding the object must be rapidly accelerated
Law of Reaction
· ____________________________________________________
As we place force on a surface by walking over it, the
surface provides an equal resistance back in the opposite direction
to the soles of our feet
Our feet push down & back, while the surface pushes
up & forward
· Force of the surface reacting to the force we place on
it is ground reaction force
Law of Reaction
· We provide the action force while the surface provides
the reaction force
easier to run on a hard track than on a sandy beach due
to the difference in the ground reaction forces of the two surfaces
track resists the runner's propulsion force, and the reaction
drives the runner ahead
Law of Reaction
sand dissipates the runner's force reducing the reaction
force with the apparent loss in forward force & speed
sprinter applies a force in excess of 300 pounds on his
starting blocks, which resist with an equal force
in flight, movement of one part of the body produces a reaction
in another part because there is no resistive surface to supply
a reaction force
Balance, equilibrium, & stability
· Balance - _________________________________________________
· Equilibrium - _____________________________________________
static or dynamic
· Static equilibrium - __________________________________________
· Dynamic equilibrium - _______________________________________________
· To control equilibrium & achieve balance, stability
needs to be maximized
· Stability is the resistance to a
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Balance, equilibrium, & stability
· Stability is enhanced by determining body's _________________________________
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· Center of gravity - _____________________________________________________
· Balance - important in resting & moving bodies
Balance, equilibrium, & stability
· Generally, balance is desired
· Some circumstances exist where movement is improved when
the body tends to be unbalanced
· General factors applicable to enhancing equilibrium,
maximizing stability, & ultimately achieving balance:
1. A person has balance when _____________________________________________
Balance, equilibrium, & stability
2. A person has balance __________________________________________________
The larger the base of support, ________________________
3. A person has balance depending on _____________________
The greater the weight, ___________________
4. A person has balance, _________________________________________
The lower the center of gravity, _______________________________
5. A person has balance, depending on
Balance is less if the center of gravity is near ________________________
When anticipating an oncoming force, stability may be improved by ________________________________________________________________________
Balance, equilibrium, & stability
6. In anticipation of an oncoming force, stability may be increased
by ________________________________________________________________________
7. Equilibrium may be enhanced by increasing the ________________________________________________________________________
8. Rotation about an axis aids balance
A moving bike is easier to balance than a stationary bike
9. Kinesthetic physiological functions contribute to balance
The semicircular canals of the inner ear, vision, touch (pressure),
& kinesthetic sense all provide balance information to the
performer
Balance and its components of equilibrium and stability are
essential in all movements and are all affected by the constant
force of gravity as well as by inertia
· In walking a person throws the body in and out of balance
with each step
· In rapid running movements where moving inertia is high,
the center of gravity has to be lowered to maintain balance when
stopping or changing direction
· In jumping activities the center of gravity needs to
be raised as high as possible
Force
· Muscles are the main source of force that produces or
changes movement of a body segment, the entire body, or some object
thrown, struck, or stopped
· Strong muscles are able to produce more force than weak
muscles
both maximum and sustained exertion over a period of time
Force
· Forces either push or pull on an object in an
attempt to affect motion or shape
· Without forces acting on an object there would be no
motion
· Force - product of mass times acceleration
· Mass - amount of matter in a body
Force
· The weight of a body segment or the entire body X the
speed of acceleration determines the force
Important in football
Also important in activities using only a part of the body
In throwing a ball, the force applied to the ball is equal
to the weight of the arm times the speed of acceleration of the
arm
Leverage factors are also important
Force
Force =
F =
· Momentum (quantity of motion) - equal to _______________________
· The greater the momentum, the ________________________________
Force
· Many activities, particularly upper extremity, require
a summation of forces from the beginning of movement in the lower
segment of the body to the twisting of the trunk and movement
at the shoulder, elbow, and wrist joints
· Ex. golf drive, shot-putting, discus and javelin throwing
Mechanical loading basics
· Significant mechanical loads are generated & absorbed
by the tissues of the body
· Internal or external forces may causing these loads
· Only muscles can actively generate internal force, but
tension in tendons, connective tissues, ligaments, and joints
capsules may generate passive internal forces
Mechanical loading basics
· External forces are produced from outside the body &
originate from gravity, inertia, or direct contact
· All tissues, in varying degrees, resist changes in their
shape
· Tissue deformation may result from external forces, but
can result from internally generated forces
Mechanical loading basics
· Internal forces can
fracture bones
dislocate joints
disrupt muscles & connective tissues
· To prevent injury or damage from tissue deformation the
body must be used to absorb energy from both internal & external
forces
Mechanical loading basics
· It is advantageous to absorb force over larger aspects
of our body rather than smaller and to spread the absorption rate
over a greater period of time
· Stronger & healthier tissues are more likely to withstand
excessive mechanical loading & the resultant excessive tissue
deformation
Mechanical loading basics
· Excessive tissue deformation due to mechanical loading
may result from
Tension (stretching or strain)
Compression
Shear
Bending
Torsion (twisting)
Throwing
· In the performance of various sport skills such as throwing,
many applications of the laws of leverage, motion, and balance
may be found
· In throwing, the angular motion of the levers (bones)
of the body (trunk, shoulder, elbow, and wrist) is used to give
linear motion to the ball when it is released
Throwing
· In throwing, the individual's inertia & the ball's
inertia must be overcome by the application of force (Law of
inertia)
· Muscles of the body provide the force to move the
body parts & the ball
· Law of acceleration is in effect with the muscular
force necessary to accelerate the arm, wrist, & hand
Throwing
· The greater the force (mass X acceleration) that a person
can produce, the faster the arm will move, and thus the greater
the speed that will be imparted to the ball
· The reaction of the feet against the surface on which
the subject stands applies the law of reaction
Throwing
· The longer the lever, the greater the speed that can
be imparted to the ball
The body from the feet to the fingers can be considered
as one long lever
The longer the lever, from natural body length or the body
movements to the extended backward position, the greater will
be the arc through which it accelerates and thus the greater the
speed imparted to the thrown object
Throwing
· Short levers are advantageous in taking less total time
to release the ball
· Balance or equilibrium is a factor in throwing when the
body is rotated posteriorly in the beginning of the throw
the body is moved nearly out of balance to the rear,
balance changes again with the forward movement
balance is reestablished with the follow-through when the
feet are spread and the knees & trunk are flexed to lower
the center of gravity