CHAPTER 21:CHAPTER 21:IMPACTIMPACT

CHAPTER 21:CHAPTER 21:IMPACTIMPACT

KINESIOLOGYScientific Basis of Human Motion, 12th edition

Hamilton, Weimar & LuttgensPresentation Created by

TK Koesterer, Ph.D., ATCHumboldt State University

Revised by Hamilton & Weimar

KINESIOLOGYScientific Basis of Human Motion, 12th edition

Hamilton, Weimar & LuttgensPresentation Created by

TK Koesterer, Ph.D., ATCHumboldt State University

Revised by Hamilton & Weimar

Copyright © 2012 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill/Irwin

21-221-2

ObjectivesObjectives

1. Name common problems associated with the diverse forms of receiving impact.

2. Explain how the work-energy, impulse-momentum, and pressure-area relationships apply to receiving impact either of one’s own body or of external objects.

3. State the principles related to avoiding injury while receiving impact and furnish an application for each.

1. Name common problems associated with the diverse forms of receiving impact.

2. Explain how the work-energy, impulse-momentum, and pressure-area relationships apply to receiving impact either of one’s own body or of external objects.

3. State the principles related to avoiding injury while receiving impact and furnish an application for each.

21-321-3

ObjectivesObjectives

4. State the principles related to maintaining and regaining equilibrium while receiving impact and furnish an application for each.

5. State the principles related to accuracy & control while receiving impact & furnish an application for each.

4. State the principles related to maintaining and regaining equilibrium while receiving impact and furnish an application for each.

5. State the principles related to accuracy & control while receiving impact & furnish an application for each.

21-421-4

MEANING OF IMPACT AND ITS’ RECEPTION MEANING OF IMPACT AND ITS’ RECEPTION

Derived from the Latin word impingere, “to press together”.

Further defined as force of contact, violent collision, striking together.

Receiving impact is opposing in some manner the force with which a moving body tends to maintain its speed and direction.

Some impacts have a positive effect, such as stimulating bone development.

Derived from the Latin word impingere, “to press together”.

Further defined as force of contact, violent collision, striking together.

Receiving impact is opposing in some manner the force with which a moving body tends to maintain its speed and direction.

Some impacts have a positive effect, such as stimulating bone development.

21-521-5

ProblemsProblems

Problems in receiving impact:1. Avoiding injury.2. Maintaining equilibrium.3. Receiving the object with accuracy

and control.

Problems in receiving impact:1. Avoiding injury.2. Maintaining equilibrium.3. Receiving the object with accuracy

and control.

21-621-6

ConceptsConcepts

1. Kinetic energy-work relationship:

When a body or object is “received” work is done equal in amount to the change in kinetic energy of the moving body.

(KE = Fd)

1. Kinetic energy-work relationship:

When a body or object is “received” work is done equal in amount to the change in kinetic energy of the moving body.

(KE = Fd)

21-721-7

ConceptsConcepts

2. Momentum-impulse relationship:

Any change in momentum requires a force applied over a period of time (impulse) and is equal to the product of the force and the time.

(Ft = Δmv)

2. Momentum-impulse relationship:

Any change in momentum requires a force applied over a period of time (impulse) and is equal to the product of the force and the time.

(Ft = Δmv)

21-821-8

ConceptsConcepts

3. Pressure-area relationship: The pressure that any part of

the body must absorb is inversely proportional to the area over which the force is applied.

(P = F/a)

3. Pressure-area relationship: The pressure that any part of

the body must absorb is inversely proportional to the area over which the force is applied.

(P = F/a)

21-921-9

Falls and LandingsFalls and Landings Important contributors to the gradual

decrease in momentum without injury: Landing on “giving” surfaces; mats. Controlled flexion at the joints of the

landing extremities through eccentric contraction of the antagonist muscles, activated prior to landing.

Relationship of the force of impact to the size of the area that bears the brunt of the impact.

Important contributors to the gradual decrease in momentum without injury: Landing on “giving” surfaces; mats. Controlled flexion at the joints of the

landing extremities through eccentric contraction of the antagonist muscles, activated prior to landing.

Relationship of the force of impact to the size of the area that bears the brunt of the impact.

21-1021-10

Regaining EquilibriumRegaining Equilibrium

Control the placement of the limbs in preparation for landing. Requires control to place the feet, or hands

and feet, in a position that will provide an adequate base of support.

Adequate base of support needs to be established.

Depends on the integrity of the bones and joints that receive the force of impact.

Control the placement of the limbs in preparation for landing. Requires control to place the feet, or hands

and feet, in a position that will provide an adequate base of support.

Adequate base of support needs to be established.

Depends on the integrity of the bones and joints that receive the force of impact.

21-1121-11

Protective EquipmentProtective Equipment

The goal of most protective equipment is to1. take a blow from a relatively small point of

contact and dissipate or distribute that force over a greater surface area and

2. use a compressible material to dissipate/absorb the shock of the impact.

By increasing the time over which the force is applied, a smaller force is required to bring about the same change in momentum.

The goal of most protective equipment is to1. take a blow from a relatively small point of

contact and dissipate or distribute that force over a greater surface area and

2. use a compressible material to dissipate/absorb the shock of the impact.

By increasing the time over which the force is applied, a smaller force is required to bring about the same change in momentum.

21-1221-12

Protective Equipment:Helmets

Protective Equipment:Helmets

Helmets are designed to protect the head, particularly the brain

Classified as: Single impact Multi-impact

More foam is not better more foam moves the hard shell further away from

the skull and leaves the head and neck open to greater rotational forces.

The foam should be soft enough to be comfortable but dense enough not to completely flatten during impact.

Helmets are designed to protect the head, particularly the brain

Classified as: Single impact Multi-impact

More foam is not better more foam moves the hard shell further away from

the skull and leaves the head and neck open to greater rotational forces.

The foam should be soft enough to be comfortable but dense enough not to completely flatten during impact.

21-1321-13

Protective Equipment:Body Protection

Protective Equipment:Body Protection

Uses the dispersal of forces over larger areas; less force per unit area.

Pads that cover joints dissipate forces over increased

surface area. use deformation of foam to absorb

energy of impact.

Uses the dispersal of forces over larger areas; less force per unit area.

Pads that cover joints dissipate forces over increased

surface area. use deformation of foam to absorb

energy of impact.

21-1421-14

Catching: Avoiding InjuryCatching: Avoiding Injury

Achieved by increasing the distance over which the object’s kinetic energy is lost. By moving the hands toward the body through

a distance of 10” to 20” as a ball is received, the catcher is making it possible for the ball’s kinetic energy to be lost gradually. (F = KE/d)

Hand position: Fingers should be pointed either down or up, according to whether the ball is below or above the waist, respectively.

Achieved by increasing the distance over which the object’s kinetic energy is lost. By moving the hands toward the body through

a distance of 10” to 20” as a ball is received, the catcher is making it possible for the ball’s kinetic energy to be lost gradually. (F = KE/d)

Hand position: Fingers should be pointed either down or up, according to whether the ball is below or above the waist, respectively.

21-1521-15

Catching: Maintaining Equilibrium

Catching: Maintaining Equilibrium

Widen the base of support in the direction of the ball’s flight. Allows weight shift from forward to

rear foot at impact. Increases chances of maintaining

equilibrium, and contributes to gradual reduction of ball’s motion.

Widen the base of support in the direction of the ball’s flight. Allows weight shift from forward to

rear foot at impact. Increases chances of maintaining

equilibrium, and contributes to gradual reduction of ball’s motion.

21-1621-16

Catching: Accuracy and Control

Catching: Accuracy and Control

Accurate vision, judgement, and positioning of the body are of vital importance. “Keeping the eye on the ball”.

Accurate judgement depends on accurate vision, and accurate adjustment of body position, as well as on agility and smoothness of neuromuscular response. “Hand-eye” & “foot-eye coordination”.

Accurate vision, judgement, and positioning of the body are of vital importance. “Keeping the eye on the ball”.

Accurate judgement depends on accurate vision, and accurate adjustment of body position, as well as on agility and smoothness of neuromuscular response. “Hand-eye” & “foot-eye coordination”.

21-1721-17

PRINCIPLES OF RECEIVING IMPACT

PRINCIPLES OF RECEIVING IMPACT

Related to Avoiding Injury

The more gradual the loss of momentum (or kinetic energy) of the moving body or object, the less the force exerted on the body.

(F = Δmv/t)

Related to Avoiding Injury

The more gradual the loss of momentum (or kinetic energy) of the moving body or object, the less the force exerted on the body.

(F = Δmv/t)Fig 21.1Fig 21.1

21-1821-18

PRINCIPLES OF RECEIVING IMPACT

PRINCIPLES OF RECEIVING IMPACT

Related to Avoiding Injury

Fig 21.3Fig 21.3Fig 21.2Fig 21.2

21-1921-19

PRINCIPLES OF RECEIVING IMPACT

PRINCIPLES OF RECEIVING IMPACT

Related to Avoiding Injury2. The larger the area receiving the

impact, the less will be the force per unit of surface area.

3. Repeated impacts may lead to overuse injures. Attention should be given to the nature of the landing surface.

Related to Avoiding Injury2. The larger the area receiving the

impact, the less will be the force per unit of surface area.

3. Repeated impacts may lead to overuse injures. Attention should be given to the nature of the landing surface.

21-2021-20

PRINCIPLES OF RECEIVING IMPACT

PRINCIPLES OF RECEIVING IMPACT

Related to Maintaining and Regaining Equilibrium

4. The larger the base of support in the direction of the impact, the greater will be the body’s equilibrium.

Related to Maintaining and Regaining Equilibrium

4. The larger the base of support in the direction of the impact, the greater will be the body’s equilibrium.

Fig 21.4Fig 21.4

21-2121-21

PRINCIPLES OF RECEIVING IMPACT

PRINCIPLES OF RECEIVING IMPACT

Related to Maintaining and Regaining Equilibrium

5. At the moment of impact, the line of gravity should be lowered & centered above the base.

Related to Maintaining and Regaining Equilibrium

5. At the moment of impact, the line of gravity should be lowered & centered above the base.

Fig 21.5Fig 21.5

21-2221-22

PRINCIPLES OF RECEIVING IMPACT

PRINCIPLES OF RECEIVING IMPACT

Related to Accuracy and Control6. The more gradually the loss of velocity

of an external object, the less likely the object is to rebound when impact is received.

7. “Keep the eye on the ball” enables one to judge speed and direction and to respond accordingly.

Related to Accuracy and Control6. The more gradually the loss of velocity

of an external object, the less likely the object is to rebound when impact is received.

7. “Keep the eye on the ball” enables one to judge speed and direction and to respond accordingly.

21-2321-23

PRINCIPLES OF RECEIVING IMPACT

PRINCIPLES OF RECEIVING IMPACT

Related to Accuracy and ControlRelated to Accuracy and Control

Fig 21.6Fig 21.6

8.8. Catching an external Catching an external object with accuracy and object with accuracy and control depends largely control depends largely on the position of the on the position of the catcher relative to the catcher relative to the direction of the direction of the approaching object.approaching object.

8.8. Catching an external Catching an external object with accuracy and object with accuracy and control depends largely control depends largely on the position of the on the position of the catcher relative to the catcher relative to the direction of the direction of the approaching object.approaching object.