Transcript 14.hamilton11e_ppt_17

Chapter 17:
Moving Objects:
Pushing and Pulling
KINESIOLOGY
Scientific Basis of Human Motion, 11th edition
Hamilton, Weimar & Luttgens
Presentation Created by
TK Koesterer, Ph.D., ATC
Humboldt State University
Revised by Hamilton & Weimar
© 2008 McGraw-Hill Higher Education. All Rights Reserved.
Objectives
Classify activity involving push or pull
patterns to the nature of the force
application.
2. Name and discuss anatomical and
mechanical factors and principles that apply
to representative push or pull activities.
3. Analyze the performance of someone
performing a push-pull skill under each of
these force application conditions:
momentary contact, projection, or
continuous application.
1.
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PUSHING AND PULLING
Joint Action Patterns

The basic joint actions are flexion and
extension in one or more of the extremities.
 These joint motions produce a rectilinear path
of motion at the distal end point of the
segments involved.
 Rectilinear path: all forces are applied directly
to the object in the direction of motion.
 Force may be applied directly or indirectly to
an object.
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Nature of Force Application
Momentary Contact
Striking and hitting.
 Contact made with an
object by moving part of
body or implement.
 Object may be stationary
or moving.

Fig 17.1
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Projection
Development of
kinetic energy in a
movable object held
in the hand.
 Followed by the
release of the object.

Fig 17.2
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Continuous Application
Continuous
application of force,
usually by hand.
 Moving a large
resistance.

Fig 17.3
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PRINCIPLES OF PUSHING
AND PULLING MOTIONS
Motion involves imparting a force,
described in terms of its magnitude,
direction, and point of application.
 These aspects of force provide the
basis of the principles that apply to
giving motion to objects or bodies
through pushing and pulling.

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Principles Relating to the
Magnitude of Force
1.
The object will move only if the force is
of sufficient magnitude to overcome
the object’s inertia.The force must
overcome not only the mass of the
object, but also;
a)
b)
c)
friction between object and supporting
surface.
resistance to surrounding medium.
internal resistance.
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Principles Relating to the
Magnitude of Force
2.
3.
Force exerted by the body will be
transferred to an external object in
proportion to the effectiveness of the
counterforce of the feet against the ground.
Optimum summation of internal force is
needed if maximum force is to be applied to
move an object. (Maximum number of
segments moved through largest ROM.)
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Principles Relating to the
Magnitude of Force
4.
5.
For maximum accuracy, the smallest
possible number of segments should
be used through the smallest possible
ROM.
For a change in momentum to occur,
force must be applied over time.
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Principles Relating to the
Direction of Force
The direction in which the object moves is
determined by the direction of the force
applied to it.
2. If an object is forced to move only along a
predetermined pathway, any component of
force not in the direction of this pathway is
wasted and may serve to increase friction.
3. When optimum force production is the
purpose, those segments involved should be
aligned with the direction of intended force
production.
1.
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Principles Relating to the Point
at Which the Force is Applied
Force applied in line with an object’s center
of gravity will result in linear motion.
2. Force applied not in line with an object’s
center of gravity will result in rotary motion.
3. If the free motion of an object is interfered
with by friction or by the presence of an
obstacle, rotary motion may result, even
though the force is applied in line with the
object’s center of gravity.
1.
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PUSH-PULL APPLICATIONS
Pushing and Pulling

The magnitude of force used in pushing,
pulling, and lifting can be increased in two
ways:
1.
2.

Using the lower extremities.
Using body weight to supplement the force
provided by the upper extremities.
Economy of effort is when force is applied in
line with object’s center of gravity and in the
direction of motion.
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Pushing an Object

The horizontal push
should be applied
close to the object’s
center of gravity at a
point found by
experimentation.
Fig 17.4
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Pulling an Object

It may be advantageous to pull in a
slightly upward direction because lifting
effect would help to reduce friction.
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Lifting
Is a form of pulling.
 Minimizing the resistance arm will
reduce the amount of effort needed to
lift object.

Fig 17.5
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Lifting

Several factors must be considered for safe,
efficient lifting:
1.
2.
3.
4.
5.
6.
Reduce load mass as much as possible.
Avoid loads at floor level to reduce trunk
bending.
The farther the load is from the involved joints,
the greater the resistance arm. Keep loads close
to the body.
Maintain a neutral posture of the spine.
Avoid trunk rotation & lateral flexion while lifting
to reduce stress on the spine.
Maintain constant lift velocity to avoid
acceleration forces.
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Holding and Carrying
Holding: effort can be minimized by
supporting the object from underneath,
with only enough force applied to
counteract the downward pull of gravity.
 Carrying: most efficient manner is that
which requires the least accommodation
of the body’s center of gravity.

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Weight Lifting
Depending on lift, either a push or a pull
pattern may be used.
 The key to safe and successful weight
lifting is in arranging the various levers
involved in such a way as to minimize
the torque produced by the external
resistance while maximizing the
available muscle torques.

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Punching





Simultaneous push pattern motions.
Usually directed horizontally.
Usually terminates with contact.
Since momentum is to be transferred to the
opponent, it is desirable for punch velocity to
be high.
Simultaneous nature allows for maximum
force production with a straight-line motion.
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Working with
Long-Handled Implements

Involves a combination of pushing, pulling,
and, in some instances, lifting.
 Back and forth motion: tendency to lean
forward.
 Although implement is light, the forward
position means a long resistance arm and
added resistance on back muscles.
 When shoveling, slide one hand down the
shaft to reduce lever arm.
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ANALYSIS OF
ERGOMETER ROWING


The motion is a combination of leg
push and arm pull in a continuous
cycle.
Two primary phases;
1.
2.
Drive phase
Recovery phase
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Drive Phase





Rower starts with slide in forward position.
Starting position: knees and hips fully flexed,
shoulders flexed, and elbows in extension.
Initiated through extension of legs, pushing
body backward.
As legs near full extension, spine begins
extension to maintain smooth, continuous
motion.
Arms now begin motion, pulling arms in.
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Recovery Phase
Leg flexion is produced by a fairly
moderate concentric contraction of
flexor muscles.
 The forward reach of the upper
extremity is produced by similar
contraction of appropriate muscles.

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Mechanical Analysis
Primary objective is to produce
maximum power.
 Generate the highest possible velocity
through a combination of stroke length
and stroke rate.
 Effective performance is when force can
be applied through the full ROM and at
the fastest possible stroke rate.

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Chapter 17:
Moving Objects:
Pushing and Pulling
© 2008 McGraw-Hill Higher Education. All Rights Reserved.