Transcript Ch16 Powerpoint

CHAPTER 16:
MOVING OBJECTS:
PUSHING AND PULLING
KINESIOLOGY
Scientific Basis of Human Motion, 12th edition
Hamilton, Weimar & Luttgens
Presentation Created by
TK Koesterer, Ph.D., ATC
Humboldt State University
Revised by Hamilton & Weimar
McGraw-Hill/Irwin
Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved.
Objectives
1. 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.
16-2
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.
16-3
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 16.1a
16-4
Projection
 Development of kinetic
energy in a movable
object held in the
hand.
 Followed by the
release of the object.
Fig 16.2
16-5
Continuous Application
 Continuous application
of force, usually by
hand.
 Moving a large
resistance.
Fig 16.3
16-6
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.
16-7
Principles Relating to the
Magnitude of Force
1. The object will move only if the force is
of large enough to overcome the
object’s inertia.The force must
overcome not only the mass, but also;
a) friction between object and supporting
surface.
b) resistance of surrounding medium.
c) internal resistance.
16-8
Principles Relating to the
Magnitude of Force
2. Force exerted by the body will be
transferred to an external object in
proportion to the counterforce of the feet
against the ground.
3. 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.)
16-9
Principles Relating to the
Magnitude of Force
4. For maximum accuracy, the smallest
possible number of segments should
be used through the smallest possible
ROM.
5. For a change in momentum to occur,
force must be applied over time.
16-10
Principles Relating to the
Direction of Force
1. The direction in which the object moves is
determined by the direction of the applied
resultant force.
2. If an object is forced to move along a
predetermined pathway, any component of
force not in the pathway direction is wasted
and may serve to increase friction.
3. When optimum force production is the
purpose, segments involved should be
aligned with the direction of force production.
16-11
Principles Relating to the Point
at Which the Force is Applied
1. 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.
16-12
PUSH-PULL APPLICATIONS
Pushing and Pulling

The magnitude of force used in pushing,
pulling, and lifting can be increased in two
ways:
1. Using the lower extremities.
2. 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.
16-13
Pushing an Object
 The horizontal push
should be applied close
to the cabinet’s center
of gravity, often at a
point found by
experimentation.
Fig 16.4
16-14
Pulling an Object
 It may be advantageous to pull in a
slightly upward direction because lifting
helps to reduce friction.
16-15
Lifting
 Is a form of pulling.
 Minimizing the resistance arm reduces
the amount of effort needed.
Fig 16.5
16-16
Lifting

Several factors must be considered for safe,
efficient lifting:
1. Reduce load mass as much as possible.
2. Avoid loads at floor level to reduce trunk
bending.
3. The farther the load is from the involved joints,
the greater the resistance arm. Keep loads close
to the body.
4. Maintain a neutral spine posture.
5. Avoid trunk rotation & lateral flexion while lifting
to reduce stress on the spine.
6. Maintain constant lift velocity to avoid
acceleration forces.
16-17
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.
16-18
Backpacks
 If the weight in the backpack exceeds
20% of body weight changes in gait
and posture will occur.
 Asymmetrical loading should be
avoided. When this is not possible an
ankle strategy should be used to adapt
posture.
16-19
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 levers involved
to minimize the torque produced by the
external resistance while maximizing
the available muscle torques.
16-20
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.




16-21
Working with
Long-Handled Implements
 Involve a combination of pushing, pulling,
and, is 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 load on back muscles.
 When shoveling, slide one hand down the
shaft to reduce the resistance arm.
16-22
ANALYSIS OF
ERGOMETER ROWING


The motion is a combination of leg
push and arm pull in a continuous
cycle.
Two primary phases;
1. Drive phase
2. Recovery phase
16-23
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.
16-24
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 the retraction
(recoil) of the cables.
16-25
Mechanical Analysis
 Primary objective is 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.
16-26